diff --git a/app/BUILD.bazel b/app/BUILD.bazel
index 9389c372c45..730a3ac2151 100644
--- a/app/BUILD.bazel
+++ b/app/BUILD.bazel
@@ -209,6 +209,7 @@ VIEW_MODELS_WITH_RESOURCE_IMPORTS = [
     "src/main/java/org/oppia/android/app/onboarding/OnboadingSlideViewModel.kt",
     "src/main/java/org/oppia/android/app/onboarding/OnboardingViewModel.kt",
     "src/main/java/org/oppia/android/app/ongoingtopiclist/OngoingTopicItemViewModel.kt",
+    "src/main/java/org/oppia/android/app/options/OptionsReadingTextSizeViewModel.kt",
     "src/main/java/org/oppia/android/app/options/TextSizeItemViewModel.kt",
     "src/main/java/org/oppia/android/app/parser/FractionParsingUiError.kt",
     "src/main/java/org/oppia/android/app/parser/StringToNumberParser.kt",
@@ -298,7 +299,6 @@ VIEW_MODELS = [
     "src/main/java/org/oppia/android/app/options/OptionsAppLanguageViewModel.kt",
     "src/main/java/org/oppia/android/app/options/OptionsAudioLanguageViewModel.kt",
     "src/main/java/org/oppia/android/app/options/OptionsItemViewModel.kt",
-    "src/main/java/org/oppia/android/app/options/OptionsReadingTextSizeViewModel.kt",
     "src/main/java/org/oppia/android/app/options/ReadingTextSizeSelectionViewModel.kt",
     "src/main/java/org/oppia/android/app/player/exploration/ExplorationViewModel.kt",
     "src/main/java/org/oppia/android/app/player/state/itemviewmodel/ContentViewModel.kt",
@@ -679,6 +679,7 @@ kt_android_library(
         "//domain/src/main/java/org/oppia/android/domain/clipboard:clipboard_controller",
         "//domain/src/main/java/org/oppia/android/domain/onboarding:state_controller",
         "//domain/src/main/java/org/oppia/android/domain/profile:profile_management_controller",
+        "//model/src/main/proto:arguments_java_proto_lite",
         "//third_party:androidx_core_core",
         "//third_party:androidx_databinding_databinding-common",
         "//third_party:androidx_databinding_databinding-runtime",
diff --git a/app/src/main/java/org/oppia/android/app/home/RouteToExplorationListener.kt b/app/src/main/java/org/oppia/android/app/home/RouteToExplorationListener.kt
index 80614517973..3c8081a3152 100755
--- a/app/src/main/java/org/oppia/android/app/home/RouteToExplorationListener.kt
+++ b/app/src/main/java/org/oppia/android/app/home/RouteToExplorationListener.kt
@@ -1,13 +1,16 @@
 package org.oppia.android.app.home
 
+import org.oppia.android.app.model.ExplorationActivityParams
+import org.oppia.android.app.model.ProfileId
+
 /** Listener for when an activity should route to a exploration. */
 interface RouteToExplorationListener {
   fun routeToExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     isCheckpointingEnabled: Boolean
   )
 }
diff --git a/app/src/main/java/org/oppia/android/app/home/recentlyplayed/RecentlyPlayedActivity.kt b/app/src/main/java/org/oppia/android/app/home/recentlyplayed/RecentlyPlayedActivity.kt
index d3e139f5d61..f16686ae092 100644
--- a/app/src/main/java/org/oppia/android/app/home/recentlyplayed/RecentlyPlayedActivity.kt
+++ b/app/src/main/java/org/oppia/android/app/home/recentlyplayed/RecentlyPlayedActivity.kt
@@ -8,6 +8,7 @@ import org.oppia.android.app.activity.ActivityComponentImpl
 import org.oppia.android.app.activity.ActivityIntentFactories
 import org.oppia.android.app.activity.InjectableAppCompatActivity
 import org.oppia.android.app.home.RouteToExplorationListener
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
 import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.player.exploration.ExplorationActivity
@@ -48,42 +49,42 @@ class RecentlyPlayedActivity :
   }
 
   override fun routeToExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     isCheckpointingEnabled: Boolean
   ) {
     startActivity(
       ExplorationActivity.createExplorationActivityIntent(
         this,
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         isCheckpointingEnabled
       )
     )
   }
 
   override fun routeToResumeLesson(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     explorationCheckpoint: ExplorationCheckpoint
   ) {
     startActivity(
       ResumeLessonActivity.createResumeLessonActivityIntent(
         this,
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         explorationCheckpoint
       )
     )
diff --git a/app/src/main/java/org/oppia/android/app/home/recentlyplayed/RecentlyPlayedFragmentPresenter.kt b/app/src/main/java/org/oppia/android/app/home/recentlyplayed/RecentlyPlayedFragmentPresenter.kt
index 386d5ddcd0a..9c00b790290 100755
--- a/app/src/main/java/org/oppia/android/app/home/recentlyplayed/RecentlyPlayedFragmentPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/home/recentlyplayed/RecentlyPlayedFragmentPresenter.kt
@@ -14,6 +14,7 @@ import org.oppia.android.R
 import org.oppia.android.app.fragment.FragmentScope
 import org.oppia.android.app.home.RouteToExplorationListener
 import org.oppia.android.app.model.ChapterPlayState
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
 import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.model.PromotedActivityList
@@ -237,6 +238,9 @@ class RecentlyPlayedFragmentPresenter @Inject constructor(
   }
 
   fun onOngoingStoryClicked(promotedStory: PromotedStory) {
+    val profileId = ProfileId.newBuilder().apply {
+      internalId = internalProfileId
+    }.build()
     val canHavePartialProgressSaved =
       when (promotedStory.chapterPlayState) {
         ChapterPlayState.IN_PROGRESS_SAVED, ChapterPlayState.IN_PROGRESS_NOT_SAVED,
@@ -248,10 +252,7 @@ class RecentlyPlayedFragmentPresenter @Inject constructor(
     if (promotedStory.chapterPlayState == ChapterPlayState.IN_PROGRESS_SAVED) {
       val explorationCheckpointLiveData =
         explorationCheckpointController.retrieveExplorationCheckpoint(
-          ProfileId.newBuilder().apply {
-            internalId = internalProfileId
-          }.build(),
-          promotedStory.explorationId
+          profileId, promotedStory.explorationId
         ).toLiveData()
 
       explorationCheckpointLiveData.observe(
@@ -261,11 +262,11 @@ class RecentlyPlayedFragmentPresenter @Inject constructor(
             if (it is AsyncResult.Success) {
               explorationCheckpointLiveData.removeObserver(this)
               routeToResumeLessonListener.routeToResumeLesson(
-                internalProfileId,
+                profileId,
                 promotedStory.topicId,
                 promotedStory.storyId,
                 promotedStory.explorationId,
-                backflowScreen = null,
+                parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED,
                 explorationCheckpoint = it.value
               )
             } else if (it is AsyncResult.Failure) {
@@ -320,11 +321,11 @@ class RecentlyPlayedFragmentPresenter @Inject constructor(
         is AsyncResult.Success -> {
           oppiaLogger.d("RecentlyPlayedFragment", "Successfully loaded exploration")
           routeToExplorationListener.routeToExploration(
-            internalProfileId,
+            ProfileId.newBuilder().apply { internalId = internalProfileId }.build(),
             topicId,
             storyId,
             explorationId,
-            backflowScreen = null,
+            parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED,
             isCheckpointingEnabled = canHavePartialProgressSaved
           )
           activity.finish()
diff --git a/app/src/main/java/org/oppia/android/app/options/LoadReadingTextSizeListener.kt b/app/src/main/java/org/oppia/android/app/options/LoadReadingTextSizeListener.kt
index 66a233a97ac..136616923c3 100644
--- a/app/src/main/java/org/oppia/android/app/options/LoadReadingTextSizeListener.kt
+++ b/app/src/main/java/org/oppia/android/app/options/LoadReadingTextSizeListener.kt
@@ -1,6 +1,12 @@
 package org.oppia.android.app.options
 
+import org.oppia.android.app.model.ReadingTextSize
+
 /** Listener for when an activity should load a [ReadingTextSizeFragment]. */
 interface LoadReadingTextSizeListener {
-  fun loadReadingTextSizeFragment(textSize: String)
+  /**
+   * Loads a tablet UI panel for changing the current UI reading text size (with the current text
+   * size being passed in via [textSize]).
+   */
+  fun loadReadingTextSizeFragment(textSize: ReadingTextSize)
 }
diff --git a/app/src/main/java/org/oppia/android/app/options/OptionControlsViewModel.kt b/app/src/main/java/org/oppia/android/app/options/OptionControlsViewModel.kt
index acb9712e054..9b1b96c564a 100644
--- a/app/src/main/java/org/oppia/android/app/options/OptionControlsViewModel.kt
+++ b/app/src/main/java/org/oppia/android/app/options/OptionControlsViewModel.kt
@@ -12,7 +12,7 @@ import org.oppia.android.app.model.AppLanguage
 import org.oppia.android.app.model.AudioLanguage
 import org.oppia.android.app.model.Profile
 import org.oppia.android.app.model.ProfileId
-import org.oppia.android.app.model.ReadingTextSize
+import org.oppia.android.app.translation.AppLanguageResourceHandler
 import org.oppia.android.app.viewmodel.ObservableArrayList
 import org.oppia.android.domain.oppialogger.OppiaLogger
 import org.oppia.android.domain.profile.ProfileManagementController
@@ -28,7 +28,8 @@ class OptionControlsViewModel @Inject constructor(
   activity: AppCompatActivity,
   private val profileManagementController: ProfileManagementController,
   private val oppiaLogger: OppiaLogger,
-  @EnableLanguageSelectionUi private val enableLanguageSelectionUi: PlatformParameterValue<Boolean>
+  @EnableLanguageSelectionUi private val enableLanguageSelectionUi: PlatformParameterValue<Boolean>,
+  private val resourceHandler: AppLanguageResourceHandler
 ) : OptionsItemViewModel() {
   private val itemViewModelList: ObservableList<OptionsItemViewModel> = ObservableArrayList()
   private lateinit var profileId: ProfileId
@@ -84,11 +85,12 @@ class OptionControlsViewModel @Inject constructor(
   }
 
   private fun processProfileList(profile: Profile): List<OptionsItemViewModel> {
-
     itemViewModelList.clear()
 
     val optionsReadingTextSizeViewModel =
-      OptionsReadingTextSizeViewModel(routeToReadingTextSizeListener, loadReadingTextSizeListener)
+      OptionsReadingTextSizeViewModel(
+        routeToReadingTextSizeListener, loadReadingTextSizeListener, resourceHandler
+      )
     val optionsAppLanguageViewModel =
       OptionsAppLanguageViewModel(routeToAppLanguageListListener, loadAppLanguageListListener)
     val optionAudioViewViewModel =
@@ -97,7 +99,7 @@ class OptionControlsViewModel @Inject constructor(
         loadAudioLanguageListListener
       )
 
-    optionsReadingTextSizeViewModel.readingTextSize.set(getReadingTextSize(profile.readingTextSize))
+    optionsReadingTextSizeViewModel.readingTextSize.set(profile.readingTextSize)
     optionsAppLanguageViewModel.appLanguage.set(getAppLanguage(profile.appLanguage))
     optionAudioViewViewModel.audioLanguage.set(getAudioLanguage(profile.audioLanguage))
 
@@ -126,15 +128,6 @@ class OptionControlsViewModel @Inject constructor(
     this.isFirstOpen = isFirstOpen
   }
 
-  fun getReadingTextSize(readingTextSize: ReadingTextSize): String {
-    return when (readingTextSize) {
-      ReadingTextSize.SMALL_TEXT_SIZE -> "Small"
-      ReadingTextSize.MEDIUM_TEXT_SIZE -> "Medium"
-      ReadingTextSize.LARGE_TEXT_SIZE -> "Large"
-      else -> "Extra Large"
-    }
-  }
-
   fun getAppLanguage(appLanguage: AppLanguage): String {
     return when (appLanguage) {
       AppLanguage.ENGLISH_APP_LANGUAGE -> "English"
diff --git a/app/src/main/java/org/oppia/android/app/options/OptionsActivity.kt b/app/src/main/java/org/oppia/android/app/options/OptionsActivity.kt
index 10c6d366fd4..32898ba060d 100644
--- a/app/src/main/java/org/oppia/android/app/options/OptionsActivity.kt
+++ b/app/src/main/java/org/oppia/android/app/options/OptionsActivity.kt
@@ -8,7 +8,10 @@ import org.oppia.android.R
 import org.oppia.android.app.activity.ActivityComponentImpl
 import org.oppia.android.app.activity.InjectableAppCompatActivity
 import org.oppia.android.app.drawer.NAVIGATION_PROFILE_ID_ARGUMENT_KEY
+import org.oppia.android.app.model.ReadingTextSize
+import org.oppia.android.app.model.ReadingTextSizeActivityResultBundle
 import org.oppia.android.app.translation.AppLanguageResourceHandler
+import org.oppia.android.util.extensions.getProtoExtra
 import org.oppia.android.util.extensions.getStringFromBundle
 import javax.inject.Inject
 
@@ -82,17 +85,23 @@ class OptionsActivity :
 
   override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
     super.onActivityResult(requestCode, resultCode, data)
+    checkNotNull(data) {
+      "Expected data to be passed as an activity result for request: $requestCode."
+    }
     when (requestCode) {
       REQUEST_CODE_TEXT_SIZE -> {
-        val textSize = data!!.getStringExtra(MESSAGE_READING_TEXT_SIZE_ARGUMENT_KEY) as String
-        optionActivityPresenter.updateReadingTextSize(textSize)
+        val textSizeResults = data.getProtoExtra(
+          MESSAGE_READING_TEXT_SIZE_RESULTS_KEY,
+          ReadingTextSizeActivityResultBundle.getDefaultInstance()
+        )
+        optionActivityPresenter.updateReadingTextSize(textSizeResults.selectedReadingTextSize)
       }
       REQUEST_CODE_APP_LANGUAGE -> {
-        val appLanguage = data!!.getStringExtra(MESSAGE_APP_LANGUAGE_ARGUMENT_KEY) as String
+        val appLanguage = data.getStringExtra(MESSAGE_APP_LANGUAGE_ARGUMENT_KEY) as String
         optionActivityPresenter.updateAppLanguage(appLanguage)
       }
       else -> {
-        val audioLanguage = data!!.getStringExtra(MESSAGE_AUDIO_LANGUAGE_ARGUMENT_KEY) as String
+        val audioLanguage = data.getStringExtra(MESSAGE_AUDIO_LANGUAGE_ARGUMENT_KEY) as String
         optionActivityPresenter.updateAudioLanguage(audioLanguage)
       }
     }
@@ -120,18 +129,14 @@ class OptionsActivity :
     )
   }
 
-  override fun routeReadingTextSize(readingTextSize: String?) {
+  override fun routeReadingTextSize(readingTextSize: ReadingTextSize) {
     startActivityForResult(
-      ReadingTextSizeActivity.createReadingTextSizeActivityIntent(
-        this,
-        READING_TEXT_SIZE,
-        readingTextSize
-      ),
+      ReadingTextSizeActivity.createReadingTextSizeActivityIntent(this, readingTextSize),
       REQUEST_CODE_TEXT_SIZE
     )
   }
 
-  override fun loadReadingTextSizeFragment(textSize: String) {
+  override fun loadReadingTextSizeFragment(textSize: ReadingTextSize) {
     selectedFragment = READING_TEXT_SIZE_FRAGMENT
     optionActivityPresenter.setExtraOptionTitle(
       resourceHandler.getStringInLocale(R.string.reading_text_size)
diff --git a/app/src/main/java/org/oppia/android/app/options/OptionsActivityPresenter.kt b/app/src/main/java/org/oppia/android/app/options/OptionsActivityPresenter.kt
index 2bce5d2fb5c..6654e2e935e 100644
--- a/app/src/main/java/org/oppia/android/app/options/OptionsActivityPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/options/OptionsActivityPresenter.kt
@@ -9,6 +9,7 @@ import androidx.drawerlayout.widget.DrawerLayout
 import org.oppia.android.R
 import org.oppia.android.app.activity.ActivityScope
 import org.oppia.android.app.drawer.NavigationDrawerFragment
+import org.oppia.android.app.model.ReadingTextSize
 import javax.inject.Inject
 
 /** The presenter for [OptionsActivity]. */
@@ -79,7 +80,7 @@ class OptionsActivityPresenter @Inject constructor(
       ) as OptionsFragment?
   }
 
-  fun updateReadingTextSize(textSize: String) {
+  fun updateReadingTextSize(textSize: ReadingTextSize) {
     getOptionFragment()?.updateReadingTextSize(textSize)
   }
 
@@ -91,7 +92,7 @@ class OptionsActivityPresenter @Inject constructor(
     getOptionFragment()?.updateAudioLanguage(audioLanguage)
   }
 
-  fun loadReadingTextSizeFragment(textSize: String) {
+  fun loadReadingTextSizeFragment(textSize: ReadingTextSize) {
     val readingTextSizeFragment = ReadingTextSizeFragment.newInstance(textSize)
     activity.supportFragmentManager
       .beginTransaction()
diff --git a/app/src/main/java/org/oppia/android/app/options/OptionsFragment.kt b/app/src/main/java/org/oppia/android/app/options/OptionsFragment.kt
index 0e11b55bdc5..a573a79027c 100644
--- a/app/src/main/java/org/oppia/android/app/options/OptionsFragment.kt
+++ b/app/src/main/java/org/oppia/android/app/options/OptionsFragment.kt
@@ -7,10 +7,11 @@ import android.view.View
 import android.view.ViewGroup
 import org.oppia.android.app.fragment.FragmentComponentImpl
 import org.oppia.android.app.fragment.InjectableFragment
+import org.oppia.android.app.model.ReadingTextSize
 import org.oppia.android.util.extensions.getStringFromBundle
 import javax.inject.Inject
 
-const val MESSAGE_READING_TEXT_SIZE_ARGUMENT_KEY = "OptionsFragment.message_reading_text_size"
+const val MESSAGE_READING_TEXT_SIZE_RESULTS_KEY = "OptionsFragment.message_reading_text_size"
 const val MESSAGE_APP_LANGUAGE_ARGUMENT_KEY = "OptionsFragment.message_app_language"
 const val MESSAGE_AUDIO_LANGUAGE_ARGUMENT_KEY = "OptionsFragment.message_audio_language"
 const val REQUEST_CODE_TEXT_SIZE = 1
@@ -66,7 +67,7 @@ class OptionsFragment : InjectableFragment() {
     )
   }
 
-  fun updateReadingTextSize(textSize: String) {
+  fun updateReadingTextSize(textSize: ReadingTextSize) {
     optionsFragmentPresenter.runAfterUIInitialization {
       optionsFragmentPresenter.updateReadingTextSize(textSize)
     }
diff --git a/app/src/main/java/org/oppia/android/app/options/OptionsFragmentPresenter.kt b/app/src/main/java/org/oppia/android/app/options/OptionsFragmentPresenter.kt
index 369f0efa623..cf019653dd2 100644
--- a/app/src/main/java/org/oppia/android/app/options/OptionsFragmentPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/options/OptionsFragmentPresenter.kt
@@ -26,7 +26,6 @@ import org.oppia.android.util.data.DataProviders.Companion.toLiveData
 import java.security.InvalidParameterException
 import javax.inject.Inject
 
-const val READING_TEXT_SIZE = "READING_TEXT_SIZE"
 const val APP_LANGUAGE = "APP_LANGUAGE"
 const val AUDIO_LANGUAGE = "AUDIO_LANGUAGE"
 private const val READING_TEXT_SIZE_TAG = "ReadingTextSize"
@@ -52,7 +51,6 @@ class OptionsFragmentPresenter @Inject constructor(
   private lateinit var recyclerViewAdapter: RecyclerView.Adapter<*>
   private var internalProfileId: Int = -1
   private lateinit var profileId: ProfileId
-  private var readingTextSize = ReadingTextSize.SMALL_TEXT_SIZE
   private var appLanguage = AppLanguage.ENGLISH_APP_LANGUAGE
   private var audioLanguage = AudioLanguage.NO_AUDIO
   private val viewModel = getOptionControlsItemViewModel()
@@ -185,86 +183,20 @@ class OptionsFragmentPresenter @Inject constructor(
     VIEW_TYPE_AUDIO_LANGUAGE
   }
 
-  fun updateReadingTextSize(textSize: String) {
-    when (textSize) {
-      getOptionControlsItemViewModel().getReadingTextSize(ReadingTextSize.SMALL_TEXT_SIZE) -> {
-        profileManagementController.updateReadingTextSize(
-          profileId,
-          ReadingTextSize.SMALL_TEXT_SIZE
-        ).toLiveData().observe(
-          fragment,
-          Observer {
-            when (it) {
-              is AsyncResult.Success -> readingTextSize = ReadingTextSize.SMALL_TEXT_SIZE
-              is AsyncResult.Failure -> {
-                oppiaLogger.e(
-                  READING_TEXT_SIZE_TAG, "$READING_TEXT_SIZE_ERROR: small text size", it.error
-                )
-              }
-              is AsyncResult.Pending -> {} // Wait for a result.
-            }
-          }
-        )
-      }
-      getOptionControlsItemViewModel().getReadingTextSize(ReadingTextSize.MEDIUM_TEXT_SIZE) -> {
-        profileManagementController.updateReadingTextSize(
-          profileId,
-          ReadingTextSize.MEDIUM_TEXT_SIZE
-        ).toLiveData().observe(
-          fragment,
-          Observer {
-            when (it) {
-              is AsyncResult.Success -> readingTextSize = ReadingTextSize.MEDIUM_TEXT_SIZE
-              is AsyncResult.Failure -> {
-                oppiaLogger.e(
-                  READING_TEXT_SIZE_TAG, "$READING_TEXT_SIZE_ERROR: medium text size", it.error
-                )
-              }
-              is AsyncResult.Pending -> {} // Wait for a result.
-            }
-          }
-        )
-      }
-      getOptionControlsItemViewModel().getReadingTextSize(ReadingTextSize.LARGE_TEXT_SIZE) -> {
-        profileManagementController.updateReadingTextSize(
-          profileId,
-          ReadingTextSize.LARGE_TEXT_SIZE
-        ).toLiveData().observe(
-          fragment,
-          Observer {
-            when (it) {
-              is AsyncResult.Success -> readingTextSize = ReadingTextSize.LARGE_TEXT_SIZE
-              is AsyncResult.Failure -> {
-                oppiaLogger.e(
-                  READING_TEXT_SIZE_TAG, "$READING_TEXT_SIZE_ERROR: large text size", it.error
-                )
-              }
-              is AsyncResult.Pending -> {} // Wait for a result.
-            }
-          }
-        )
-      }
-      getOptionControlsItemViewModel()
-        .getReadingTextSize(ReadingTextSize.EXTRA_LARGE_TEXT_SIZE) -> {
-        profileManagementController.updateReadingTextSize(
-          profileId,
-          ReadingTextSize.EXTRA_LARGE_TEXT_SIZE
-        ).toLiveData().observe(
-          fragment,
-          Observer {
-            when (it) {
-              is AsyncResult.Success -> readingTextSize = ReadingTextSize.EXTRA_LARGE_TEXT_SIZE
-              is AsyncResult.Failure -> {
-                oppiaLogger.e(
-                  READING_TEXT_SIZE_TAG, "$READING_TEXT_SIZE_ERROR: extra large text size", it.error
-                )
-              }
-              is AsyncResult.Pending -> {} // Wait for a result.
-            }
+  fun updateReadingTextSize(textSize: ReadingTextSize) {
+    profileManagementController.updateReadingTextSize(profileId, textSize).toLiveData().observe(
+      fragment,
+      {
+        when (it) {
+          is AsyncResult.Failure -> {
+            oppiaLogger.e(
+              READING_TEXT_SIZE_TAG, "$READING_TEXT_SIZE_ERROR: updating to $textSize", it.error
+            )
           }
-        )
+          else -> {} // Nothing needs to be done unless the update failed.
+        }
       }
-    }
+    )
     recyclerViewAdapter.notifyItemChanged(0)
   }
 
diff --git a/app/src/main/java/org/oppia/android/app/options/OptionsReadingTextSizeViewModel.kt b/app/src/main/java/org/oppia/android/app/options/OptionsReadingTextSizeViewModel.kt
index 39014f849de..626069bec7f 100644
--- a/app/src/main/java/org/oppia/android/app/options/OptionsReadingTextSizeViewModel.kt
+++ b/app/src/main/java/org/oppia/android/app/options/OptionsReadingTextSizeViewModel.kt
@@ -1,17 +1,29 @@
 package org.oppia.android.app.options
 
 import androidx.databinding.ObservableField
+import org.oppia.android.R
+import org.oppia.android.app.model.ReadingTextSize
+import org.oppia.android.app.translation.AppLanguageResourceHandler
 
 /** ReadingTextSize settings view model for the recycler view in [OptionsFragment]. */
 class OptionsReadingTextSizeViewModel(
   private val routeToReadingTextSizeListener: RouteToReadingTextSizeListener,
-  private val loadReadingTextSizeListener: LoadReadingTextSizeListener
+  private val loadReadingTextSizeListener: LoadReadingTextSizeListener,
+  private val resourceHandler: AppLanguageResourceHandler
 ) : OptionsItemViewModel() {
-  val readingTextSize = ObservableField<String>("")
-
-  fun setReadingTextSize(readingTextSizeValue: String) {
-    readingTextSize.set(readingTextSizeValue)
-  }
+  val readingTextSize = ObservableField(ReadingTextSize.TEXT_SIZE_UNSPECIFIED)
+  val textSizeName: String
+    get() {
+      return when (readingTextSize.get()!!) {
+        ReadingTextSize.SMALL_TEXT_SIZE ->
+          resourceHandler.getStringInLocale(R.string.reading_text_size_small)
+        ReadingTextSize.MEDIUM_TEXT_SIZE ->
+          resourceHandler.getStringInLocale(R.string.reading_text_size_medium)
+        ReadingTextSize.LARGE_TEXT_SIZE ->
+          resourceHandler.getStringInLocale(R.string.reading_text_size_large)
+        else -> resourceHandler.getStringInLocale(R.string.reading_text_size_extra_large)
+      }
+    }
 
   fun loadReadingTextSizeFragment() {
     loadReadingTextSizeListener.loadReadingTextSizeFragment(readingTextSize.get()!!)
@@ -21,7 +33,7 @@ class OptionsReadingTextSizeViewModel(
     if (isMultipane.get()!!) {
       loadReadingTextSizeListener.loadReadingTextSizeFragment(readingTextSize.get()!!)
     } else {
-      routeToReadingTextSizeListener.routeReadingTextSize(readingTextSize.get())
+      routeToReadingTextSizeListener.routeReadingTextSize(readingTextSize.get()!!)
     }
   }
 }
diff --git a/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeActivity.kt b/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeActivity.kt
index ada56a940b2..9b6658567e8 100644
--- a/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeActivity.kt
+++ b/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeActivity.kt
@@ -5,8 +5,19 @@ import android.content.Intent
 import android.os.Bundle
 import org.oppia.android.app.activity.ActivityComponentImpl
 import org.oppia.android.app.activity.InjectableAppCompatActivity
+import org.oppia.android.app.model.ReadingTextSize
+import org.oppia.android.app.model.ReadingTextSizeActivityParams
+import org.oppia.android.app.model.ReadingTextSizeActivityResultBundle
+import org.oppia.android.app.model.ReadingTextSizeActivityStateBundle
+import org.oppia.android.util.extensions.getProto
+import org.oppia.android.util.extensions.getProtoExtra
+import org.oppia.android.util.extensions.putProto
+import org.oppia.android.util.extensions.putProtoExtra
 import javax.inject.Inject
 
+private const val ACTIVITY_PARAMS_KEY = "ReadingTextSizeActivity.params"
+private const val ACTIVITY_SAVED_STATE_KEY = "ReadingTextSizeActivity.saved_state"
+
 /** The activity to change the text size of the reading content in the app. */
 class ReadingTextSizeActivity : InjectableAppCompatActivity() {
 
@@ -16,54 +27,53 @@ class ReadingTextSizeActivity : InjectableAppCompatActivity() {
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     (activityComponent as ActivityComponentImpl).inject(this)
-    val prefSummaryValue = (
-      if (savedInstanceState != null) {
-        savedInstanceState.get(KEY_READING_TEXT_SIZE_PREFERENCE_SUMMARY_VALUE)
-      } else {
-        intent.getStringExtra(KEY_READING_TEXT_SIZE_PREFERENCE_SUMMARY_VALUE)
-      }
-      ) as String
-    readingTextSizeActivityPresenter.handleOnCreate(prefSummaryValue)
+
+    val readingTextSize =
+      savedInstanceState?.retrieveStateBundle()?.selectedReadingTextSize
+        ?: retrieveActivityParams().readingTextSize
+    readingTextSizeActivityPresenter.handleOnCreate(readingTextSize)
   }
 
   companion object {
-    internal const val KEY_READING_TEXT_SIZE_PREFERENCE_TITLE = "READING_TEXT_SIZE_PREFERENCE"
-    const val KEY_READING_TEXT_SIZE_PREFERENCE_SUMMARY_VALUE =
-      "READING_TEXT_SIZE_PREFERENCE_SUMMARY_VALUE"
     /** Returns a new [Intent] to route to [ReadingTextSizeActivity]. */
     fun createReadingTextSizeActivityIntent(
       context: Context,
-      prefKey: String,
-      summaryValue: String?
+      initialReadingTextSize: ReadingTextSize
     ): Intent {
-      val intent = Intent(context, ReadingTextSizeActivity::class.java)
-      intent.putExtra(KEY_READING_TEXT_SIZE_PREFERENCE_TITLE, prefKey)
-      intent.putExtra(KEY_READING_TEXT_SIZE_PREFERENCE_SUMMARY_VALUE, summaryValue)
-      return intent
-    }
-
-    fun getKeyReadingTextSizePreferenceTitle(): String {
-      return KEY_READING_TEXT_SIZE_PREFERENCE_TITLE
-    }
-
-    fun getKeyReadingTextSizePreferenceSummaryValue(): String {
-      return KEY_READING_TEXT_SIZE_PREFERENCE_SUMMARY_VALUE
+      val params = ReadingTextSizeActivityParams.newBuilder().apply {
+        readingTextSize = initialReadingTextSize
+      }.build()
+      return Intent(context, ReadingTextSizeActivity::class.java).apply {
+        putProtoExtra(ACTIVITY_PARAMS_KEY, params)
+      }
     }
   }
 
   override fun onSaveInstanceState(outState: Bundle) {
     super.onSaveInstanceState(outState)
-    outState.putString(
-      KEY_READING_TEXT_SIZE_PREFERENCE_SUMMARY_VALUE,
-      readingTextSizeActivityPresenter.getSelectedReadingTextSize()
-    )
+    val stateBundle = ReadingTextSizeActivityStateBundle.newBuilder().apply {
+      selectedReadingTextSize = readingTextSizeActivityPresenter.getSelectedReadingTextSize()
+    }.build()
+    outState.putProto(ACTIVITY_SAVED_STATE_KEY, stateBundle)
   }
 
   override fun onBackPressed() {
-    val message = readingTextSizeActivityPresenter.getSelectedReadingTextSize()
-    val intent = Intent()
-    intent.putExtra(MESSAGE_READING_TEXT_SIZE_ARGUMENT_KEY, message)
+    val resultBundle = ReadingTextSizeActivityResultBundle.newBuilder().apply {
+      selectedReadingTextSize = readingTextSizeActivityPresenter.getSelectedReadingTextSize()
+    }.build()
+    val intent = Intent().apply {
+      putProtoExtra(MESSAGE_READING_TEXT_SIZE_RESULTS_KEY, resultBundle)
+    }
     setResult(REQUEST_CODE_TEXT_SIZE, intent)
     finish()
   }
+
+  private fun retrieveActivityParams() =
+    intent.getProtoExtra(ACTIVITY_PARAMS_KEY, ReadingTextSizeActivityParams.getDefaultInstance())
+
+  private fun Bundle.retrieveStateBundle(): ReadingTextSizeActivityStateBundle {
+    return getProto(
+      ACTIVITY_SAVED_STATE_KEY, ReadingTextSizeActivityStateBundle.getDefaultInstance()
+    )
+  }
 }
diff --git a/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeActivityPresenter.kt b/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeActivityPresenter.kt
index 8039a711f2e..3ab661a3ced 100644
--- a/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeActivityPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeActivityPresenter.kt
@@ -4,6 +4,7 @@ import androidx.appcompat.app.AppCompatActivity
 import androidx.appcompat.widget.Toolbar
 import org.oppia.android.R
 import org.oppia.android.app.activity.ActivityScope
+import org.oppia.android.app.model.ReadingTextSize
 import javax.inject.Inject
 
 /** The presenter for [ReadingTextSizeActivity]. */
@@ -11,14 +12,14 @@ import javax.inject.Inject
 class ReadingTextSizeActivityPresenter @Inject constructor(
   private val activity: AppCompatActivity
 ) {
-  private lateinit var fontSize: String
+  private lateinit var fontSize: ReadingTextSize
 
-  fun handleOnCreate(prefSummaryValue: String) {
+  fun handleOnCreate(preferredTextSize: ReadingTextSize) {
     activity.setContentView(R.layout.reading_text_size_activity)
     setToolbar()
-    fontSize = prefSummaryValue
+    fontSize = preferredTextSize
     if (getReadingTextSizeFragment() == null) {
-      val readingTextSizeFragment = ReadingTextSizeFragment.newInstance(prefSummaryValue)
+      val readingTextSizeFragment = ReadingTextSizeFragment.newInstance(preferredTextSize)
       activity.supportFragmentManager.beginTransaction()
         .add(R.id.reading_text_size_container, readingTextSizeFragment).commitNow()
     }
@@ -31,11 +32,11 @@ class ReadingTextSizeActivityPresenter @Inject constructor(
     }
   }
 
-  fun setSelectedReadingTextSize(fontSize: String) {
+  fun setSelectedReadingTextSize(fontSize: ReadingTextSize) {
     this.fontSize = fontSize
   }
 
-  fun getSelectedReadingTextSize(): String {
+  fun getSelectedReadingTextSize(): ReadingTextSize {
     return fontSize
   }
 
diff --git a/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeFragment.kt b/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeFragment.kt
index 3547a7362e8..1cdae8c8578 100644
--- a/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeFragment.kt
+++ b/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeFragment.kt
@@ -7,12 +7,15 @@ import android.view.View
 import android.view.ViewGroup
 import org.oppia.android.app.fragment.FragmentComponentImpl
 import org.oppia.android.app.fragment.InjectableFragment
+import org.oppia.android.app.model.ReadingTextSize
+import org.oppia.android.app.model.ReadingTextSizeFragmentArguments
+import org.oppia.android.app.model.ReadingTextSizeFragmentStateBundle
+import org.oppia.android.util.extensions.getProto
+import org.oppia.android.util.extensions.putProto
 import javax.inject.Inject
 
-private const val READING_TEXT_SIZE_PREFERENCE_SUMMARY_VALUE_ARGUMENT_KEY =
-  "ReadingTextSizeFragment.reading_text_size_preference_summary_value"
-private const val SELECTED_READING_TEXT_SIZE_SAVED_KEY =
-  "ReadingTextSizeFragment.selected_text_size"
+private const val FRAGMENT_ARGUMENTS_KEY = "ReadingTextSizeFragment.arguments"
+private const val FRAGMENT_SAVED_STATE_KEY = "ReadingTextSizeFragment.saved_state"
 
 /** The fragment to change the text size of the reading content in the app. */
 class ReadingTextSizeFragment : InjectableFragment(), TextSizeRadioButtonListener {
@@ -20,12 +23,15 @@ class ReadingTextSizeFragment : InjectableFragment(), TextSizeRadioButtonListene
   lateinit var readingTextSizeFragmentPresenter: ReadingTextSizeFragmentPresenter
 
   companion object {
-    fun newInstance(readingTextSize: String): ReadingTextSizeFragment {
-      val args = Bundle()
-      args.putString(READING_TEXT_SIZE_PREFERENCE_SUMMARY_VALUE_ARGUMENT_KEY, readingTextSize)
-      val fragment = ReadingTextSizeFragment()
-      fragment.arguments = args
-      return fragment
+    fun newInstance(readingTextSize: ReadingTextSize): ReadingTextSizeFragment {
+      val protoArguments = ReadingTextSizeFragmentArguments.newBuilder().apply {
+        this.readingTextSize = readingTextSize
+      }.build()
+      return ReadingTextSizeFragment().apply {
+        arguments = Bundle().apply {
+          putProto(FRAGMENT_ARGUMENTS_KEY, protoArguments)
+        }
+      }
     }
   }
 
@@ -39,25 +45,33 @@ class ReadingTextSizeFragment : InjectableFragment(), TextSizeRadioButtonListene
     container: ViewGroup?,
     savedInstanceState: Bundle?
   ): View? {
-    val args =
-      checkNotNull(arguments) { "Expected arguments to be passed to ReadingTextSizeFragment" }
-    val readingTextSize = if (savedInstanceState == null) {
-      args.get(READING_TEXT_SIZE_PREFERENCE_SUMMARY_VALUE_ARGUMENT_KEY) as String
-    } else {
-      savedInstanceState.get(SELECTED_READING_TEXT_SIZE_SAVED_KEY) as String
-    }
+    val readingTextSize =
+      savedInstanceState?.retrieveStateBundle()?.selectedReadingTextSize
+        ?: retrieveFragmentArguments().readingTextSize
     return readingTextSizeFragmentPresenter.handleOnCreateView(inflater, container, readingTextSize)
   }
 
   override fun onSaveInstanceState(outState: Bundle) {
     super.onSaveInstanceState(outState)
-    outState.putString(
-      SELECTED_READING_TEXT_SIZE_SAVED_KEY,
-      readingTextSizeFragmentPresenter.getTextSizeSelected()
-    )
+    val stateBundle = ReadingTextSizeFragmentStateBundle.newBuilder().apply {
+      selectedReadingTextSize = readingTextSizeFragmentPresenter.getTextSizeSelected()
+    }.build()
+    outState.putProto(FRAGMENT_SAVED_STATE_KEY, stateBundle)
   }
 
-  override fun onTextSizeSelected(selectedTextSize: String) {
+  override fun onTextSizeSelected(selectedTextSize: ReadingTextSize) {
     readingTextSizeFragmentPresenter.onTextSizeSelected(selectedTextSize)
   }
+
+  private fun retrieveFragmentArguments(): ReadingTextSizeFragmentArguments {
+    return checkNotNull(arguments) {
+      "Expected arguments to be passed to ReadingTextSizeFragment"
+    }.getProto(FRAGMENT_ARGUMENTS_KEY, ReadingTextSizeFragmentArguments.getDefaultInstance())
+  }
+
+  private fun Bundle.retrieveStateBundle(): ReadingTextSizeFragmentStateBundle {
+    return getProto(
+      FRAGMENT_SAVED_STATE_KEY, ReadingTextSizeFragmentStateBundle.getDefaultInstance()
+    )
+  }
 }
diff --git a/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeFragmentPresenter.kt b/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeFragmentPresenter.kt
index 79fb3be6870..1331a2577c3 100644
--- a/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeFragmentPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeFragmentPresenter.kt
@@ -4,9 +4,8 @@ import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
 import androidx.fragment.app.Fragment
-import org.oppia.android.R
+import org.oppia.android.app.model.ReadingTextSize
 import org.oppia.android.app.recyclerview.BindableAdapter
-import org.oppia.android.app.translation.AppLanguageResourceHandler
 import org.oppia.android.databinding.ReadingTextSizeFragmentBinding
 import org.oppia.android.databinding.TextSizeItemsBinding
 import javax.inject.Inject
@@ -14,17 +13,12 @@ import javax.inject.Inject
 /** The presenter for [ReadingTextSizeFragment]. */
 class ReadingTextSizeFragmentPresenter @Inject constructor(
   private val fragment: Fragment,
-  private val readingTextSizeSelectionViewModel: ReadingTextSizeSelectionViewModel,
-  resourceHandler: AppLanguageResourceHandler
+  private val readingTextSizeSelectionViewModel: ReadingTextSizeSelectionViewModel
 ) {
-  private var fontSize: String = resourceHandler.getStringInLocale(
-    R.string.reading_text_size_medium
-  )
-
   fun handleOnCreateView(
     inflater: LayoutInflater,
     container: ViewGroup?,
-    readingTextSize: String
+    readingTextSize: ReadingTextSize
   ): View? {
     val binding = ReadingTextSizeFragmentBinding.inflate(
       inflater,
@@ -32,20 +26,17 @@ class ReadingTextSizeFragmentPresenter @Inject constructor(
       /* attachToRoot= */ false
     )
 
-    fontSize = readingTextSize
-    updateTextSize(fontSize)
+    updateTextSize(readingTextSize)
 
     binding.viewModel = readingTextSizeSelectionViewModel
-    readingTextSizeSelectionViewModel.selectedTextSize.value = fontSize
+    readingTextSizeSelectionViewModel.selectedTextSize = readingTextSize
     binding.textSizeRecyclerView.apply {
       adapter = createRecyclerViewAdapter()
     }
     return binding.root
   }
 
-  fun getTextSizeSelected(): String? {
-    return readingTextSizeSelectionViewModel.selectedTextSize.value
-  }
+  fun getTextSizeSelected(): ReadingTextSize? = readingTextSizeSelectionViewModel.selectedTextSize
 
   private fun createRecyclerViewAdapter(): BindableAdapter<TextSizeItemViewModel> {
     return BindableAdapter.SingleTypeBuilder
@@ -57,7 +48,7 @@ class ReadingTextSizeFragmentPresenter @Inject constructor(
       ).build()
   }
 
-  private fun updateTextSize(textSize: String) {
+  private fun updateTextSize(textSize: ReadingTextSize) {
     // The first branch of (when) will be used in the case of multipane
     when (val parentActivity = fragment.activity) {
       is OptionsActivity -> parentActivity.optionActivityPresenter.updateReadingTextSize(textSize)
@@ -66,8 +57,8 @@ class ReadingTextSizeFragmentPresenter @Inject constructor(
     }
   }
 
-  fun onTextSizeSelected(selectedTextSize: String) {
-    readingTextSizeSelectionViewModel.selectedTextSize.value = selectedTextSize
+  fun onTextSizeSelected(selectedTextSize: ReadingTextSize) {
+    readingTextSizeSelectionViewModel.selectedTextSize = selectedTextSize
     updateTextSize(selectedTextSize)
   }
 }
diff --git a/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeSelectionViewModel.kt b/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeSelectionViewModel.kt
index fb8ea3fac19..a18fceedc3c 100644
--- a/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeSelectionViewModel.kt
+++ b/app/src/main/java/org/oppia/android/app/options/ReadingTextSizeSelectionViewModel.kt
@@ -12,45 +12,46 @@ import javax.inject.Inject
 @FragmentScope
 class ReadingTextSizeSelectionViewModel @Inject constructor(
   fragment: Fragment,
-  private val resourceHandler: AppLanguageResourceHandler
+  resourceHandler: AppLanguageResourceHandler
 ) : ObservableViewModel() {
 
   private val resourceBundle = fragment.requireContext().resources
-  val selectedTextSize = MutableLiveData<String>()
+  private val changeableSelectedTextSize = MutableLiveData<ReadingTextSize>()
   private val textSizeRadioButtonListener = fragment as TextSizeRadioButtonListener
+  var selectedTextSize: ReadingTextSize?
+    get() = changeableSelectedTextSize.value
+    set(value) { changeableSelectedTextSize.value = value }
 
-  private val textSizeList = listOf<TextSizeItemViewModel>(
+  private val textSizeList = listOf(
     TextSizeItemViewModel(
       resourceBundle,
       ReadingTextSize.SMALL_TEXT_SIZE,
-      selectedTextSize,
+      changeableSelectedTextSize,
       textSizeRadioButtonListener,
       resourceHandler
     ),
     TextSizeItemViewModel(
       resourceBundle,
       ReadingTextSize.MEDIUM_TEXT_SIZE,
-      selectedTextSize,
+      changeableSelectedTextSize,
       textSizeRadioButtonListener,
       resourceHandler
     ),
     TextSizeItemViewModel(
       resourceBundle,
       ReadingTextSize.LARGE_TEXT_SIZE,
-      selectedTextSize,
+      changeableSelectedTextSize,
       textSizeRadioButtonListener,
       resourceHandler
     ),
     TextSizeItemViewModel(
       resourceBundle,
       ReadingTextSize.EXTRA_LARGE_TEXT_SIZE,
-      selectedTextSize,
+      changeableSelectedTextSize,
       textSizeRadioButtonListener,
       resourceHandler
     ),
   )
 
-  val recyclerViewTextSizeList: List<TextSizeItemViewModel> by lazy {
-    textSizeList
-  }
+  val recyclerViewTextSizeList: List<TextSizeItemViewModel> by lazy { textSizeList }
 }
diff --git a/app/src/main/java/org/oppia/android/app/options/RouteToReadingTextSizeListener.kt b/app/src/main/java/org/oppia/android/app/options/RouteToReadingTextSizeListener.kt
index c1ad1c9db86..58d3c8a7902 100644
--- a/app/src/main/java/org/oppia/android/app/options/RouteToReadingTextSizeListener.kt
+++ b/app/src/main/java/org/oppia/android/app/options/RouteToReadingTextSizeListener.kt
@@ -1,6 +1,12 @@
 package org.oppia.android.app.options
 
+import org.oppia.android.app.model.ReadingTextSize
+
 /** Listener for when an activity should route to a [ReadingTextSizeActivity]. */
 interface RouteToReadingTextSizeListener {
-  fun routeReadingTextSize(readingTextSize: String?)
+  /**
+   * Loads a standalone UI for changing the current UI reading text size (with the current text size
+   * being passed in via [readingTextSize]).
+   */
+  fun routeReadingTextSize(readingTextSize: ReadingTextSize)
 }
diff --git a/app/src/main/java/org/oppia/android/app/options/TextSizeItemViewModel.kt b/app/src/main/java/org/oppia/android/app/options/TextSizeItemViewModel.kt
index a8e240609c8..1b3fda584af 100644
--- a/app/src/main/java/org/oppia/android/app/options/TextSizeItemViewModel.kt
+++ b/app/src/main/java/org/oppia/android/app/options/TextSizeItemViewModel.kt
@@ -15,9 +15,9 @@ private const val EXTRA_LARGE_TEXT_SIZE_SCALE = 1.4f
 
 /** Text Size item view model for the recycler view in [ReadingTextSizeFragment]. */
 class TextSizeItemViewModel(
-  val resources: Resources,
+  private val resources: Resources,
   val readingTextSize: ReadingTextSize,
-  private val selectedTextSize: LiveData<String>,
+  private val selectedTextSize: LiveData<ReadingTextSize>,
   val textSizeRadioButtonListener: TextSizeRadioButtonListener,
   private val resourceHandler: AppLanguageResourceHandler
 ) : ObservableViewModel() {
@@ -44,6 +44,6 @@ class TextSizeItemViewModel(
     }
   }
   val isTextSizeSelected: LiveData<Boolean> by lazy {
-    Transformations.map(selectedTextSize) { it == textSizeName }
+    Transformations.map(selectedTextSize) { it == readingTextSize }
   }
 }
diff --git a/app/src/main/java/org/oppia/android/app/options/TextSizeRadioButtonListener.kt b/app/src/main/java/org/oppia/android/app/options/TextSizeRadioButtonListener.kt
index 821bcf3d78d..7f4daeaff10 100644
--- a/app/src/main/java/org/oppia/android/app/options/TextSizeRadioButtonListener.kt
+++ b/app/src/main/java/org/oppia/android/app/options/TextSizeRadioButtonListener.kt
@@ -1,6 +1,9 @@
 package org.oppia.android.app.options
 
+import org.oppia.android.app.model.ReadingTextSize
+
 /** Listener for when the reading text size is selected from the [ReadingTextSizeFragment]. */
 interface TextSizeRadioButtonListener {
-  fun onTextSizeSelected(selectedTextSize: String)
+  /** Called when the user selects a new [ReadingTextSize]. */
+  fun onTextSizeSelected(selectedTextSize: ReadingTextSize)
 }
diff --git a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationActivity.kt b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationActivity.kt
index 29c46c4c7bf..0bb946fad35 100755
--- a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationActivity.kt
+++ b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationActivity.kt
@@ -12,7 +12,9 @@ import org.oppia.android.app.hintsandsolution.HintsAndSolutionDialogFragment
 import org.oppia.android.app.hintsandsolution.HintsAndSolutionListener
 import org.oppia.android.app.hintsandsolution.RevealHintListener
 import org.oppia.android.app.hintsandsolution.RevealSolutionInterface
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.HelpIndex
+import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.model.ReadingTextSize
 import org.oppia.android.app.model.State
 import org.oppia.android.app.model.WrittenTranslationContext
@@ -21,6 +23,8 @@ import org.oppia.android.app.player.state.listener.RouteToHintsAndSolutionListen
 import org.oppia.android.app.player.state.listener.StateKeyboardButtonListener
 import org.oppia.android.app.player.stopplaying.StopStatePlayingSessionWithSavedProgressListener
 import org.oppia.android.app.topic.conceptcard.ConceptCardListener
+import org.oppia.android.util.extensions.getProtoExtra
+import org.oppia.android.util.extensions.putProtoExtra
 import javax.inject.Inject
 
 const val TAG_HINTS_AND_SOLUTION_DIALOG = "HINTS_AND_SOLUTION_DIALOG"
@@ -39,80 +43,63 @@ class ExplorationActivity :
   HintsAndSolutionExplorationManagerListener,
   ConceptCardListener {
 
-  @Inject
-  lateinit var explorationActivityPresenter: ExplorationActivityPresenter
-  private var internalProfileId: Int = -1
-  private lateinit var topicId: String
-  private lateinit var storyId: String
-  private lateinit var explorationId: String
+  @Inject lateinit var explorationActivityPresenter: ExplorationActivityPresenter
+
   private lateinit var state: State
   private lateinit var writtenTranslationContext: WrittenTranslationContext
-  private var backflowScreen: Int? = null
-  private var isCheckpointingEnabled: Boolean = false
 
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     (activityComponent as ActivityComponentImpl).inject(this)
-    internalProfileId = intent.getIntExtra(EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY, -1)
-    topicId = checkNotNull(intent.getStringExtra(EXPLORATION_ACTIVITY_TOPIC_ID_ARGUMENT_KEY)) {
-      "Expected $EXPLORATION_ACTIVITY_TOPIC_ID_ARGUMENT_KEY to be in intent extras."
-    }
-    storyId = checkNotNull(intent.getStringExtra(EXPLORATION_ACTIVITY_STORY_ID_ARGUMENT_KEY)) {
-      "Expected $EXPLORATION_ACTIVITY_STORY_ID_ARGUMENT_KEY to be in intent extras."
-    }
-    explorationId = checkNotNull(
-      intent.getStringExtra(
-        EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY
-      )
-    ) {
-      "Expected EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY to be in intent extras."
-    }
-    backflowScreen = intent.getIntExtra(EXPLORATION_ACTIVITY_BACKFLOW_SCREEN_KEY, -1)
-    isCheckpointingEnabled =
-      intent.getBooleanExtra(EXPLORATION_ACTIVITY_IS_CHECKPOINTING_ENABLED_KEY, false)
+
+    val params = intent.getProtoExtra(PARAMS_KEY, ExplorationActivityParams.getDefaultInstance())
     explorationActivityPresenter.handleOnCreate(
       this,
-      internalProfileId,
-      topicId,
-      storyId,
-      explorationId,
-      backflowScreen,
-      isCheckpointingEnabled
+      params.profileId,
+      params.topicId,
+      params.storyId,
+      params.explorationId,
+      params.parentScreen,
+      params.isCheckpointingEnabled
     )
   }
 
   // TODO(#1655): Re-restrict access to fields in tests post-Gradle.
   companion object {
-    /** Returns a new [Intent] to route to [ExplorationActivity] for a specified exploration. */
-
-    const val EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY =
-      "ExplorationActivity.profile_id"
-    const val EXPLORATION_ACTIVITY_TOPIC_ID_ARGUMENT_KEY = "ExplorationActivity.topic_id"
-    const val EXPLORATION_ACTIVITY_STORY_ID_ARGUMENT_KEY = "ExplorationActivity.story_id"
-    const val EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY =
-      "ExplorationActivity.exploration_id"
-    const val EXPLORATION_ACTIVITY_BACKFLOW_SCREEN_KEY =
-      "ExplorationActivity.backflow_screen"
-    const val EXPLORATION_ACTIVITY_IS_CHECKPOINTING_ENABLED_KEY =
-      "ExplorationActivity.is_checkpointing_enabled_key"
+    private const val PARAMS_KEY = "ExplorationActivity.params"
 
+    /**
+     * A convenience function for creating a new [ExplorationActivity] intent by prefilling common
+     * params needed by the activity.
+     */
     fun createExplorationActivityIntent(
       context: Context,
-      profileId: Int,
+      profileId: ProfileId,
       topicId: String,
       storyId: String,
       explorationId: String,
-      backflowScreen: Int?,
+      parentScreen: ExplorationActivityParams.ParentScreen,
       isCheckpointingEnabled: Boolean
     ): Intent {
-      val intent = Intent(context, ExplorationActivity::class.java)
-      intent.putExtra(EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY, profileId)
-      intent.putExtra(EXPLORATION_ACTIVITY_TOPIC_ID_ARGUMENT_KEY, topicId)
-      intent.putExtra(EXPLORATION_ACTIVITY_STORY_ID_ARGUMENT_KEY, storyId)
-      intent.putExtra(EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY, explorationId)
-      intent.putExtra(EXPLORATION_ACTIVITY_BACKFLOW_SCREEN_KEY, backflowScreen)
-      intent.putExtra(EXPLORATION_ACTIVITY_IS_CHECKPOINTING_ENABLED_KEY, isCheckpointingEnabled)
-      return intent
+      val params = ExplorationActivityParams.newBuilder().apply {
+        this.profileId = profileId
+        this.topicId = topicId
+        this.storyId = storyId
+        this.explorationId = explorationId
+        this.parentScreen = parentScreen
+        this.isCheckpointingEnabled = isCheckpointingEnabled
+      }.build()
+      return createExplorationActivityIntent(context, params)
+    }
+
+    /** Returns a new [Intent] open an [ExplorationActivity] with the specified [params]. */
+    fun createExplorationActivityIntent(
+      context: Context,
+      params: ExplorationActivityParams
+    ): Intent {
+      return Intent(context, ExplorationActivity::class.java).apply {
+        putProtoExtra(PARAMS_KEY, params)
+      }
     }
   }
 
diff --git a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationActivityPresenter.kt b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationActivityPresenter.kt
index de940a8518e..fd8126dc548 100755
--- a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationActivityPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationActivityPresenter.kt
@@ -1,7 +1,6 @@
 package org.oppia.android.app.player.exploration
 
 import android.content.Context
-import android.os.Bundle
 import android.view.MenuItem
 import android.view.inputmethod.EditorInfo
 import android.widget.TextView
@@ -16,6 +15,7 @@ import org.oppia.android.app.activity.ActivityScope
 import org.oppia.android.app.help.HelpActivity
 import org.oppia.android.app.model.CheckpointState
 import org.oppia.android.app.model.EphemeralExploration
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.model.ReadingTextSize
 import org.oppia.android.app.options.OptionsActivity
@@ -56,29 +56,24 @@ class ExplorationActivityPresenter @Inject constructor(
   private lateinit var storyId: String
   private lateinit var explorationId: String
   private lateinit var context: Context
-  private var backflowScreen: Int? = null
+  private lateinit var parentScreen: ExplorationActivityParams.ParentScreen
 
   private var isCheckpointingEnabled: Boolean = false
 
   private lateinit var oldestCheckpointExplorationId: String
   private lateinit var oldestCheckpointExplorationTitle: String
 
-  enum class ParentActivityForExploration(val value: Int) {
-    BACKFLOW_SCREEN_LESSONS(0),
-    BACKFLOW_SCREEN_STORY(1);
-  }
-
   private val exploreViewModel by lazy {
     getExplorationViewModel()
   }
 
   fun handleOnCreate(
     context: Context,
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     isCheckpointingEnabled: Boolean
   ) {
     val binding = DataBindingUtil.setContentView<ExplorationActivityBinding>(
@@ -106,12 +101,12 @@ class ExplorationActivityPresenter @Inject constructor(
       getExplorationFragment()?.handlePlayAudio()
     }
 
-    profileId = ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+    this.profileId = profileId
     this.topicId = topicId
     this.storyId = storyId
     this.explorationId = explorationId
     this.context = context
-    this.backflowScreen = backflowScreen
+    this.parentScreen = parentScreen
     this.isCheckpointingEnabled = isCheckpointingEnabled
     updateToolbarTitle(explorationId)
 
@@ -119,16 +114,9 @@ class ExplorationActivityPresenter @Inject constructor(
     subscribeToOldestSavedExplorationDetails()
 
     if (getExplorationManagerFragment() == null) {
-      val explorationManagerFragment = ExplorationManagerFragment()
-      val args = Bundle()
-      args.putInt(
-        ExplorationActivity.EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY,
-        internalProfileId
-      )
-      explorationManagerFragment.arguments = args
       activity.supportFragmentManager.beginTransaction().add(
         R.id.exploration_fragment_placeholder,
-        explorationManagerFragment,
+        ExplorationManagerFragment.createNewInstance(profileId),
         TAG_EXPLORATION_MANAGER_FRAGMENT
       ).commitNow()
     }
@@ -139,11 +127,7 @@ class ExplorationActivityPresenter @Inject constructor(
       activity.supportFragmentManager.beginTransaction().add(
         R.id.exploration_fragment_placeholder,
         ExplorationFragment.newInstance(
-          topicId = topicId,
-          internalProfileId = profileId.internalId,
-          storyId = storyId,
-          readingTextSize = readingTextSize.name,
-          explorationId = explorationId
+          profileId, topicId, storyId, explorationId, readingTextSize
         ),
         TAG_EXPLORATION_FRAGMENT
       ).commitNow()
@@ -167,7 +151,7 @@ class ExplorationActivityPresenter @Inject constructor(
           profileId.internalId,
           /* isFromNavigationDrawer= */ false
         )
-        fontScaleConfigurationUtil.adjustFontScale(activity, ReadingTextSize.MEDIUM_TEXT_SIZE.name)
+        fontScaleConfigurationUtil.adjustFontScale(activity, ReadingTextSize.MEDIUM_TEXT_SIZE)
         context.startActivity(intent)
         true
       }
@@ -176,7 +160,7 @@ class ExplorationActivityPresenter @Inject constructor(
           activity, profileId.internalId,
           /* isFromNavigationDrawer= */false
         )
-        fontScaleConfigurationUtil.adjustFontScale(activity, ReadingTextSize.MEDIUM_TEXT_SIZE.name)
+        fontScaleConfigurationUtil.adjustFontScale(activity, ReadingTextSize.MEDIUM_TEXT_SIZE)
         context.startActivity(intent)
         true
       }
@@ -235,7 +219,7 @@ class ExplorationActivityPresenter @Inject constructor(
   }
 
   fun stopExploration(isCompletion: Boolean) {
-    fontScaleConfigurationUtil.adjustFontScale(activity, ReadingTextSize.MEDIUM_TEXT_SIZE.name)
+    fontScaleConfigurationUtil.adjustFontScale(activity, ReadingTextSize.MEDIUM_TEXT_SIZE)
     explorationDataController.stopPlayingExploration(isCompletion).toLiveData()
       .observe(
         activity,
@@ -246,7 +230,7 @@ class ExplorationActivityPresenter @Inject constructor(
               oppiaLogger.e("ExplorationActivity", "Failed to stop exploration", it.error)
             is AsyncResult.Success -> {
               oppiaLogger.d("ExplorationActivity", "Successfully stopped exploration")
-              backPressActivitySelector(backflowScreen)
+              backPressActivitySelector()
               (activity as ExplorationActivity).finish()
             }
           }
@@ -331,17 +315,17 @@ class ExplorationActivityPresenter @Inject constructor(
     }
   }
 
-  private fun backPressActivitySelector(backflowScreen: Int?) {
-    when (backflowScreen) {
-      ParentActivityForExploration.BACKFLOW_SCREEN_STORY.value -> activity.finish()
-      ParentActivityForExploration.BACKFLOW_SCREEN_LESSONS.value -> activity.finish()
-      else -> activity.startActivity(
-        TopicActivity.createTopicActivityIntent(
-          context,
-          profileId.internalId,
-          topicId
+  private fun backPressActivitySelector() {
+    when (parentScreen) {
+      ExplorationActivityParams.ParentScreen.TOPIC_SCREEN_LESSONS_TAB,
+      ExplorationActivityParams.ParentScreen.STORY_SCREEN -> activity.finish()
+      ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED,
+      ExplorationActivityParams.ParentScreen.UNRECOGNIZED -> {
+        // Default to the topic activity.
+        activity.startActivity(
+          TopicActivity.createTopicActivityIntent(context, profileId.internalId, topicId)
         )
-      )
+      }
     }
   }
 
diff --git a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationFragment.kt b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationFragment.kt
index ddf88f38cd1..b72f2f0da61 100755
--- a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationFragment.kt
+++ b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationFragment.kt
@@ -7,8 +7,10 @@ import android.view.View
 import android.view.ViewGroup
 import org.oppia.android.app.fragment.FragmentComponentImpl
 import org.oppia.android.app.fragment.InjectableFragment
-import org.oppia.android.app.utility.FontScaleConfigurationUtil
-import org.oppia.android.util.extensions.getStringFromBundle
+import org.oppia.android.app.model.ExplorationFragmentArguments
+import org.oppia.android.app.model.ProfileId
+import org.oppia.android.app.model.ReadingTextSize
+import org.oppia.android.util.extensions.putProto
 import javax.inject.Inject
 
 /** Fragment that contains displays single exploration. */
@@ -16,81 +18,45 @@ class ExplorationFragment : InjectableFragment() {
   @Inject
   lateinit var explorationFragmentPresenter: ExplorationFragmentPresenter
 
-  @Inject
-  lateinit var fontScaleConfigurationUtil: FontScaleConfigurationUtil
-
   companion object {
-    internal const val INTERNAL_PROFILE_ID_ARGUMENT_KEY =
-      "ExplorationFragment.internal_profile_id"
-    internal const val TOPIC_ID_ARGUMENT_KEY = "ExplorationFragment.topic_id"
-    internal const val STORY_ID_ARGUMENT_KEY = "ExplorationFragment.story_id"
-    internal const val STORY_DEFAULT_FONT_SIZE_ARGUMENT_KEY =
-      "ExplorationFragment.story_default_font_size"
-    internal const val EXPLORATION_ID_ARGUMENT_KEY =
-      "ExplorationFragment.exploration_id"
-
-    /** Returns a new [ExplorationFragment] to pass the profileId, topicId, storyId, readingTextSize and explorationId. */
+    /** Returns a new [ExplorationFragment] with the corresponding fragment parameters. */
     fun newInstance(
-      internalProfileId: Int,
+      profileId: ProfileId,
       topicId: String,
       storyId: String,
-      readingTextSize: String,
-      explorationId: String
+      explorationId: String,
+      readingTextSize: ReadingTextSize
     ): ExplorationFragment {
-      val explorationFragment = ExplorationFragment()
-      val args = Bundle()
-      args.putInt(
-        INTERNAL_PROFILE_ID_ARGUMENT_KEY,
-        internalProfileId
-      )
-      args.putString(TOPIC_ID_ARGUMENT_KEY, topicId)
-      args.putString(STORY_ID_ARGUMENT_KEY, storyId)
-      args.putString(
-        STORY_DEFAULT_FONT_SIZE_ARGUMENT_KEY,
-        readingTextSize
-      )
-      args.putString(
-        EXPLORATION_ID_ARGUMENT_KEY,
-        explorationId
-      )
-      explorationFragment.arguments = args
-      return explorationFragment
+      val args = ExplorationFragmentArguments.newBuilder().apply {
+        this.profileId = profileId
+        this.topicId = topicId
+        this.storyId = storyId
+        this.explorationId = explorationId
+        this.readingTextSize = readingTextSize
+      }.build()
+      return ExplorationFragment().apply {
+        arguments = Bundle().apply {
+          putProto(ExplorationFragmentPresenter.ARGUMENTS_KEY, args)
+        }
+      }
     }
   }
 
   override fun onAttach(context: Context) {
     super.onAttach(context)
     (fragmentComponent as FragmentComponentImpl).inject(this)
-    val readingTextSize =
-      arguments!!.getStringFromBundle(STORY_DEFAULT_FONT_SIZE_ARGUMENT_KEY)
-    checkNotNull(readingTextSize) { "ExplorationFragment must be created with a reading text size" }
-    fontScaleConfigurationUtil.adjustFontScale(context, readingTextSize)
+    explorationFragmentPresenter.handleAttach(context)
   }
 
   override fun onCreateView(
     inflater: LayoutInflater,
     container: ViewGroup?,
     savedInstanceState: Bundle?
-  ): View? {
-    val profileId =
-      arguments!!.getInt(INTERNAL_PROFILE_ID_ARGUMENT_KEY, -1)
-    val topicId =
-      arguments!!.getStringFromBundle(TOPIC_ID_ARGUMENT_KEY)
-    checkNotNull(topicId) { "StateFragment must be created with an topic ID" }
-    val storyId =
-      arguments!!.getStringFromBundle(STORY_ID_ARGUMENT_KEY)
-    checkNotNull(storyId) { "StateFragment must be created with an story ID" }
-    val explorationId =
-      arguments!!.getStringFromBundle(EXPLORATION_ID_ARGUMENT_KEY)
-    checkNotNull(explorationId) { "StateFragment must be created with an exploration ID" }
-    return explorationFragmentPresenter.handleCreateView(
-      inflater,
-      container,
-      profileId,
-      topicId,
-      storyId,
-      explorationId
-    )
+  ): View = explorationFragmentPresenter.handleCreateView(inflater, container)
+
+  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
+    super.onViewCreated(view, savedInstanceState)
+    explorationFragmentPresenter.handleViewCreated()
   }
 
   fun handlePlayAudio() = explorationFragmentPresenter.handlePlayAudio()
diff --git a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationFragmentPresenter.kt b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationFragmentPresenter.kt
index 1085a5536d5..99f12480320 100755
--- a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationFragmentPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationFragmentPresenter.kt
@@ -1,34 +1,48 @@
 package org.oppia.android.app.player.exploration
 
+import android.content.Context
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
 import androidx.fragment.app.Fragment
 import org.oppia.android.R
 import org.oppia.android.app.fragment.FragmentScope
+import org.oppia.android.app.model.ExplorationFragmentArguments
+import org.oppia.android.app.model.ReadingTextSize
 import org.oppia.android.app.player.state.StateFragment
+import org.oppia.android.app.utility.FontScaleConfigurationUtil
 import org.oppia.android.databinding.ExplorationFragmentBinding
 import org.oppia.android.domain.oppialogger.OppiaLogger
+import org.oppia.android.domain.profile.ProfileManagementController
+import org.oppia.android.util.data.AsyncResult
+import org.oppia.android.util.data.DataProviders.Companion.toLiveData
+import org.oppia.android.util.extensions.getProto
+import org.oppia.android.util.extensions.putProto
 import javax.inject.Inject
 
 /** The presenter for [ExplorationFragment]. */
 @FragmentScope
 class ExplorationFragmentPresenter @Inject constructor(
   private val fragment: Fragment,
-  private val oppiaLogger: OppiaLogger
+  private val oppiaLogger: OppiaLogger,
+  private val fontScaleConfigurationUtil: FontScaleConfigurationUtil,
+  private val profileManagementController: ProfileManagementController
 ) {
-  fun handleCreateView(
-    inflater: LayoutInflater,
-    container: ViewGroup?,
-    profileId: Int,
-    topicId: String,
-    storyId: String,
-    explorationId: String
-  ): View? {
+  /** Handles the [Fragment.onAttach] portion of [ExplorationFragment]'s lifecycle. */
+  fun handleAttach(context: Context) {
+    fontScaleConfigurationUtil.adjustFontScale(context, retrieveArguments().readingTextSize)
+  }
+
+  /** Handles the [Fragment.onCreateView] portion of [ExplorationFragment]'s lifecycle. */
+  fun handleCreateView(inflater: LayoutInflater, container: ViewGroup?): View {
+    val args = retrieveArguments()
     val binding =
       ExplorationFragmentBinding.inflate(inflater, container, /* attachToRoot= */ false).root
-    val stateFragment = StateFragment.newInstance(profileId, topicId, storyId, explorationId)
-    logPracticeFragmentEvent(topicId, storyId, explorationId)
+    val stateFragment =
+      StateFragment.newInstance(
+        args.profileId.internalId, args.topicId, args.storyId, args.explorationId
+      )
+    logPracticeFragmentEvent(args.topicId, args.storyId, args.explorationId)
     if (getStateFragment() == null) {
       fragment.childFragmentManager.beginTransaction().add(
         R.id.state_fragment_placeholder,
@@ -38,6 +52,24 @@ class ExplorationFragmentPresenter @Inject constructor(
     return binding
   }
 
+  /** Handles the [Fragment.onViewCreated] portion of [ExplorationFragment]'s lifecycle. */
+  fun handleViewCreated() {
+    val profileDataProvider = profileManagementController.getProfile(retrieveArguments().profileId)
+    profileDataProvider.toLiveData().observe(
+      fragment,
+      { result ->
+        val readingTextSize = retrieveArguments().readingTextSize
+        if (result is AsyncResult.Success && result.value.readingTextSize != readingTextSize) {
+          selectNewReadingTextSize(result.value.readingTextSize)
+
+          // Since text views are based on sp for sizing, the activity needs to be recreated so that
+          // sp can be correctly recomputed.
+          fragment.requireActivity().recreate()
+        }
+      }
+    )
+  }
+
   fun handlePlayAudio() {
     getStateFragment()?.handlePlayAudio()
   }
@@ -76,4 +108,28 @@ class ExplorationFragmentPresenter @Inject constructor(
       oppiaLogger.createOpenExplorationActivityContext(topicId, storyId, explorationId)
     )
   }
+
+  private fun selectNewReadingTextSize(readingTextSize: ReadingTextSize) {
+    updateArguments(
+      retrieveArguments().toBuilder().apply {
+        this.readingTextSize = readingTextSize
+      }.build()
+    )
+    fontScaleConfigurationUtil.adjustFontScale(fragment.requireActivity(), readingTextSize)
+  }
+
+  private fun retrieveArguments(): ExplorationFragmentArguments {
+    return fragment.requireArguments().getProto(
+      ARGUMENTS_KEY, ExplorationFragmentArguments.getDefaultInstance()
+    )
+  }
+
+  private fun updateArguments(updatedArgs: ExplorationFragmentArguments) {
+    fragment.requireArguments().putProto(ARGUMENTS_KEY, updatedArgs)
+  }
+
+  companion object {
+    /** The fragment arguments key for all proto-held arguments for [ExplorationFragment]. */
+    const val ARGUMENTS_KEY = "ExplorationFragment.arguments"
+  }
 }
diff --git a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationManagerFragment.kt b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationManagerFragment.kt
index 5697b9eed99..a7775707373 100644
--- a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationManagerFragment.kt
+++ b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationManagerFragment.kt
@@ -4,6 +4,9 @@ import android.content.Context
 import android.os.Bundle
 import org.oppia.android.app.fragment.FragmentComponentImpl
 import org.oppia.android.app.fragment.InjectableFragment
+import org.oppia.android.app.model.ProfileId
+import org.oppia.android.util.extensions.getProto
+import org.oppia.android.util.extensions.putProto
 import javax.inject.Inject
 
 /**
@@ -21,11 +24,25 @@ class ExplorationManagerFragment : InjectableFragment() {
 
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
-    val internalProfileId =
-      arguments!!.getInt(
-        ExplorationActivity.EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY,
-        /* defaultValue= */ -1
-      )
-    explorationManagerFragmentPresenter.handleCreate(internalProfileId)
+    val profileId = checkNotNull(arguments) {
+      "Expected arguments to be provided for fragment."
+    }.getProto(PROFILE_ID_ARGUMENT_KEY, ProfileId.getDefaultInstance())
+    explorationManagerFragmentPresenter.handleCreate(profileId)
+  }
+
+  companion object {
+    private const val PROFILE_ID_ARGUMENT_KEY = "ExplorationManagerFragment.profile_id"
+
+    /**
+     * Returns a new instance of [ExplorationManagerFragment] corresponding to the specified
+     * [profileId].
+     */
+    fun createNewInstance(profileId: ProfileId): ExplorationManagerFragment {
+      return ExplorationManagerFragment().apply {
+        arguments = Bundle().apply {
+          putProto(PROFILE_ID_ARGUMENT_KEY, profileId)
+        }
+      }
+    }
   }
 }
diff --git a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationManagerFragmentPresenter.kt b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationManagerFragmentPresenter.kt
index 4df78475693..86dd9d370e5 100644
--- a/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationManagerFragmentPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/player/exploration/ExplorationManagerFragmentPresenter.kt
@@ -3,7 +3,6 @@ package org.oppia.android.app.player.exploration
 import androidx.appcompat.app.AppCompatActivity
 import androidx.fragment.app.Fragment
 import androidx.lifecycle.LiveData
-import androidx.lifecycle.Observer
 import androidx.lifecycle.Transformations
 import org.oppia.android.app.fragment.FragmentScope
 import org.oppia.android.app.model.Profile
@@ -25,11 +24,11 @@ class ExplorationManagerFragmentPresenter @Inject constructor(
 ) {
   private lateinit var profileId: ProfileId
 
-  fun handleCreate(internalProfileId: Int) {
-    this.profileId = ProfileId.newBuilder().setInternalId(internalProfileId).build()
+  fun handleCreate(profileId: ProfileId) {
+    this.profileId = profileId
     retrieveReadingTextSize().observe(
       fragment,
-      Observer<ReadingTextSize> { result ->
+      { result ->
         (activity as DefaultFontSizeStateListener).onDefaultFontSizeLoaded(result)
       }
     )
diff --git a/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonActivity.kt b/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonActivity.kt
index 47c11242da2..9f134a0ad4b 100644
--- a/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonActivity.kt
+++ b/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonActivity.kt
@@ -6,121 +6,89 @@ import android.os.Bundle
 import org.oppia.android.app.activity.ActivityComponentImpl
 import org.oppia.android.app.activity.InjectableAppCompatActivity
 import org.oppia.android.app.home.RouteToExplorationListener
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
+import org.oppia.android.app.model.ProfileId
+import org.oppia.android.app.model.ResumeLessonActivityParams
 import org.oppia.android.app.player.exploration.ExplorationActivity
+import org.oppia.android.util.extensions.getProtoExtra
+import org.oppia.android.util.extensions.putProtoExtra
 import javax.inject.Inject
 
 /** Activity that allows the user to resume a saved exploration. */
 class ResumeLessonActivity : InjectableAppCompatActivity(), RouteToExplorationListener {
-
-  @Inject
-  lateinit var resumeLessonActivityPresenter: ResumeLessonActivityPresenter
-  private var internalProfileId: Int = -1
-  private lateinit var topicId: String
-  private lateinit var storyId: String
-  private lateinit var explorationId: String
-  private lateinit var explorationCheckpoint: ExplorationCheckpoint
-  private var backflowScreen: Int = -1
+  @Inject lateinit var resumeLessonActivityPresenter: ResumeLessonActivityPresenter
 
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     (activityComponent as ActivityComponentImpl).inject(this)
-    internalProfileId =
-      intent.getIntExtra(RESUME_LESSON_ACTIVITY_INTERNAL_PROFILE_ID_ARGUMENT_KEY, -1)
-    topicId =
-      checkNotNull(intent.getStringExtra(RESUME_LESSON_ACTIVITY_TOPIC_ID_ARGUMENT_KEY)) {
-        "Expected topic ID to be included in intent for ResumeLessonActivity."
-      }
-    storyId =
-      checkNotNull(intent.getStringExtra(RESUME_LESSON_ACTIVITY_STORY_ID_ARGUMENT_KEY)) {
-        "Expected story ID to be included in intent for ResumeLessonActivity."
-      }
-    explorationId =
-      checkNotNull(intent.getStringExtra(RESUME_LESSON_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY)) {
-        "Expected exploration ID to be included in intent for ResumeLessonActivity."
-      }
-    backflowScreen = intent.getIntExtra(RESUME_LESSON_ACTIVITY_BACKFLOW_SCREEN_KEY, -1)
-    explorationCheckpoint = ExplorationCheckpoint.parseFrom(
-      intent.getByteArrayExtra(RESUME_LESSON_ACTIVITY_EXPLORATION_CHECKPOINT_ARGUMENT_KEY)
-    )
+
+    val params = intent.getProtoExtra(PARAMS_KEY, ResumeLessonActivityParams.getDefaultInstance())
     resumeLessonActivityPresenter.handleOnCreate(
-      internalProfileId,
-      topicId,
-      storyId,
-      explorationId,
-      backflowScreen,
-      explorationCheckpoint
+      params.profileId,
+      params.topicId,
+      params.storyId,
+      params.explorationId,
+      params.parentScreen,
+      params.checkpoint
     )
   }
 
   // TODO(#1655): Re-restrict access to fields in tests post-Gradle.
   companion object {
-    /** Argument key for internal profile ID in [ResumeLessonActivity] */
-    const val RESUME_LESSON_ACTIVITY_INTERNAL_PROFILE_ID_ARGUMENT_KEY =
-      "ResumeLessonActivity.internal_profile_id"
-
-    /** Argument key for topic ID in [ResumeLessonActivity] */
-    const val RESUME_LESSON_ACTIVITY_TOPIC_ID_ARGUMENT_KEY =
-      "ResumeLessonActivity.topic_id"
-
-    /** Argument key for story ID in [ResumeLessonActivity] */
-    const val RESUME_LESSON_ACTIVITY_STORY_ID_ARGUMENT_KEY =
-      "ResumeLessonActivity.story_id"
-
-    /** Argument key for exploration ID in [ResumeLessonActivity] */
-    const val RESUME_LESSON_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY =
-      "ResumeLessonActivity.exploration_id"
-
-    /** Argument key for backflow screen in [ResumeLessonActivity] */
-    const val RESUME_LESSON_ACTIVITY_BACKFLOW_SCREEN_KEY =
-      "ResumeLessonActivity.backflow_screen"
-
-    /** Argument key for exploration checkpoint in [ResumeLessonActivity] */
-    const val RESUME_LESSON_ACTIVITY_EXPLORATION_CHECKPOINT_ARGUMENT_KEY =
-      "ResumeLessonActivity.exploration_checkpoint"
+    private const val PARAMS_KEY = "ResumeLessonActivity.params"
 
     /**
-     * Returns a new [Intent] to route to [ResumeLessonActivity] for a specified exploration.
+     * A convenience function for creating a new [ResumeLessonActivity] intent by prefilling common
+     * params needed by the activity.
      */
     fun createResumeLessonActivityIntent(
       context: Context,
-      internalProfileId: Int,
+      profileId: ProfileId,
       topicId: String,
       storyId: String,
       explorationId: String,
-      backflowScreen: Int?,
-      explorationCheckpoint: ExplorationCheckpoint
+      parentScreen: ExplorationActivityParams.ParentScreen,
+      checkpoint: ExplorationCheckpoint
     ): Intent {
-      val intent = Intent(context, ResumeLessonActivity::class.java)
-      intent.putExtra(RESUME_LESSON_ACTIVITY_INTERNAL_PROFILE_ID_ARGUMENT_KEY, internalProfileId)
-      intent.putExtra(RESUME_LESSON_ACTIVITY_TOPIC_ID_ARGUMENT_KEY, topicId)
-      intent.putExtra(RESUME_LESSON_ACTIVITY_STORY_ID_ARGUMENT_KEY, storyId)
-      intent.putExtra(RESUME_LESSON_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY, explorationId)
-      intent.putExtra(RESUME_LESSON_ACTIVITY_BACKFLOW_SCREEN_KEY, backflowScreen)
-      intent.putExtra(
-        RESUME_LESSON_ACTIVITY_EXPLORATION_CHECKPOINT_ARGUMENT_KEY,
-        explorationCheckpoint.toByteArray()
-      )
-      return intent
+      val params = ResumeLessonActivityParams.newBuilder().apply {
+        this.profileId = profileId
+        this.topicId = topicId
+        this.storyId = storyId
+        this.explorationId = explorationId
+        this.parentScreen = parentScreen
+        this.checkpoint = checkpoint
+      }.build()
+      return createResumeLessonActivityIntent(context, params)
+    }
+
+    /** Returns a new [Intent] open an [ResumeLessonActivity] with the specified [params]. */
+    fun createResumeLessonActivityIntent(
+      context: Context,
+      params: ResumeLessonActivityParams
+    ): Intent {
+      return Intent(context, ResumeLessonActivity::class.java).apply {
+        putProtoExtra(PARAMS_KEY, params)
+      }
     }
   }
 
   override fun routeToExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     isCheckpointingEnabled: Boolean
   ) {
     startActivity(
       ExplorationActivity.createExplorationActivityIntent(
         this,
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         isCheckpointingEnabled
       )
     )
diff --git a/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonActivityPresenter.kt b/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonActivityPresenter.kt
index f05a71dd66d..4064708069e 100644
--- a/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonActivityPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonActivityPresenter.kt
@@ -3,7 +3,9 @@ package org.oppia.android.app.resumelesson
 import androidx.appcompat.app.AppCompatActivity
 import androidx.databinding.DataBindingUtil
 import org.oppia.android.R
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
+import org.oppia.android.app.model.ProfileId
 import org.oppia.android.databinding.ResumeLessonActivityBinding
 import javax.inject.Inject
 
@@ -16,11 +18,11 @@ class ResumeLessonActivityPresenter @Inject constructor(
 
   /** Handles onCreate() method of the [ResumeLessonActivity] */
   fun handleOnCreate(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     explorationCheckpoint: ExplorationCheckpoint
   ) {
     val binding = DataBindingUtil.setContentView<ResumeLessonActivityBinding>(
@@ -36,11 +38,11 @@ class ResumeLessonActivityPresenter @Inject constructor(
 
     if (getResumeLessonFragment() == null) {
       val resumeLessonFragment = ResumeLessonFragment.newInstance(
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         explorationCheckpoint
       )
       activity.supportFragmentManager.beginTransaction().add(
diff --git a/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonFragment.kt b/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonFragment.kt
index 89cfcc69210..10a05914af6 100644
--- a/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonFragment.kt
+++ b/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonFragment.kt
@@ -7,53 +7,41 @@ import android.view.View
 import android.view.ViewGroup
 import org.oppia.android.app.fragment.FragmentComponentImpl
 import org.oppia.android.app.fragment.InjectableFragment
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
+import org.oppia.android.app.model.ProfileId
+import org.oppia.android.app.model.ResumeLessonFragmentArguments
 import org.oppia.android.util.extensions.getProto
-import org.oppia.android.util.extensions.getStringFromBundle
 import org.oppia.android.util.extensions.putProto
 import javax.inject.Inject
 
 /** Fragment that allows the user to resume a saved exploration. */
 class ResumeLessonFragment : InjectableFragment() {
-
   companion object {
-    private const val RESUME_LESSON_FRAGMENT_INTERNAL_PROFILE_ID_KEY =
-      "ResumeExplorationFragmentPresenter.resume_exploration_fragment_internal_profile_id"
-    private const val RESUME_LESSON_FRAGMENT_TOPIC_ID_KEY =
-      "ResumeExplorationFragmentPresenter.resume_exploration_fragment_topic_id"
-    private const val RESUME_LESSON_FRAGMENT_STORY_ID_KEY =
-      "ResumeExplorationFragmentPresenter.resume_exploration_fragment_story_id"
-    private const val RESUME_LESSON_FRAGMENT_EXPLORATION_ID_KEY =
-      "ResumeExplorationFragmentPresenter.resume_Lesson_fragment_exploration_id"
-    private const val RESUME_LESSON_FRAGMENT_BACKFLOW_SCREEN_KEY =
-      "ResumeLessonFragmentPresenter.resume_lesson_fragment_backflow_screen"
-    private const val RESUME_LESSON_FRAGMENT_EXPLORATION_CHECKPOINT_KEY =
-      "ResumeExplorationFragmentPresenter.resume_Lesson_fragment_exploration_checkpoint"
+    private const val ARGUMENTS_KEY = "ResumeExplorationFragment.arguments"
 
-    /**
-     * Creates new instance of [ResumeLessonFragment].
-     *
-     * @param internalProfileId is used by the ResumeLessonFragment to retrieve saved checkpoint
-     * @param explorationId is used by the ResumeLessonFragment to retrieve saved checkpoint
-     */
+    /** Creates new instance of [ResumeLessonFragment] for the provided parameters. */
     fun newInstance(
-      internalProfileId: Int,
+      profileId: ProfileId,
       topicId: String,
       storyId: String,
       explorationId: String,
-      backflowScreen: Int,
-      explorationCheckpoint: ExplorationCheckpoint
+      parentScreen: ExplorationActivityParams.ParentScreen,
+      checkpoint: ExplorationCheckpoint
     ): ResumeLessonFragment {
-      val resumeLessonFragment = ResumeLessonFragment()
-      val args = Bundle()
-      args.putInt(RESUME_LESSON_FRAGMENT_INTERNAL_PROFILE_ID_KEY, internalProfileId)
-      args.putString(RESUME_LESSON_FRAGMENT_TOPIC_ID_KEY, topicId)
-      args.putString(RESUME_LESSON_FRAGMENT_STORY_ID_KEY, storyId)
-      args.putString(RESUME_LESSON_FRAGMENT_EXPLORATION_ID_KEY, explorationId)
-      args.putInt(RESUME_LESSON_FRAGMENT_BACKFLOW_SCREEN_KEY, backflowScreen)
-      args.putProto(RESUME_LESSON_FRAGMENT_EXPLORATION_CHECKPOINT_KEY, explorationCheckpoint)
-      resumeLessonFragment.arguments = args
-      return resumeLessonFragment
+      val args = ResumeLessonFragmentArguments.newBuilder().apply {
+        this.profileId = profileId
+        this.topicId = topicId
+        this.storyId = storyId
+        this.explorationId = explorationId
+        this.parentScreen = parentScreen
+        this.checkpoint = checkpoint
+      }.build()
+      return ResumeLessonFragment().apply {
+        arguments = Bundle().apply {
+          putProto(ARGUMENTS_KEY, args)
+        }
+      }
     }
   }
 
@@ -70,42 +58,18 @@ class ResumeLessonFragment : InjectableFragment() {
     container: ViewGroup?,
     savedInstanceState: Bundle?
   ): View? {
-    val internalProfileId =
-      checkNotNull(arguments?.getInt(RESUME_LESSON_FRAGMENT_INTERNAL_PROFILE_ID_KEY, -1)) {
-        "Expected profile ID to be included in arguments for ResumeLessonFragment."
-      }
-    val topicId =
-      checkNotNull(arguments?.getStringFromBundle(RESUME_LESSON_FRAGMENT_TOPIC_ID_KEY)) {
-        "Expected topic ID to be included in arguments for ResumeLessonFragment."
-      }
-    val storyId =
-      checkNotNull(arguments?.getStringFromBundle(RESUME_LESSON_FRAGMENT_STORY_ID_KEY)) {
-        "Expected story ID to be included in arguments for ResumeLessonFragment."
-      }
-    val explorationId =
-      checkNotNull(arguments?.getStringFromBundle(RESUME_LESSON_FRAGMENT_EXPLORATION_ID_KEY)) {
-        "Expected exploration ID to be included in arguments for ResumeLessonFragment."
-      }
-    val backflowScreen = arguments?.getInt(RESUME_LESSON_FRAGMENT_BACKFLOW_SCREEN_KEY, -1)
-    val explorationCheckpoint =
-      checkNotNull(
-        arguments?.getProto(
-          RESUME_LESSON_FRAGMENT_EXPLORATION_CHECKPOINT_KEY,
-          ExplorationCheckpoint.getDefaultInstance()
-        )
-      ) {
-        "Expected exploration checkpoint to be included in arguments for ResumeLessonFragment."
-      }
-
+    val args = checkNotNull(arguments) {
+      "Expected arguments to be provided for fragment."
+    }.getProto(ARGUMENTS_KEY, ResumeLessonFragmentArguments.getDefaultInstance())
     return resumeLessonFragmentPresenter.handleOnCreate(
       inflater,
       container,
-      internalProfileId,
-      topicId,
-      storyId,
-      explorationId,
-      backflowScreen,
-      explorationCheckpoint
+      args.profileId,
+      args.topicId,
+      args.storyId,
+      args.explorationId,
+      args.parentScreen,
+      args.checkpoint
     )
   }
 }
diff --git a/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonFragmentPresenter.kt b/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonFragmentPresenter.kt
index 3454050cd3f..89173f4c236 100644
--- a/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonFragmentPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/resumelesson/ResumeLessonFragmentPresenter.kt
@@ -9,6 +9,7 @@ import androidx.lifecycle.LiveData
 import androidx.lifecycle.Transformations
 import org.oppia.android.app.home.RouteToExplorationListener
 import org.oppia.android.app.model.EphemeralChapterSummary
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
 import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.translation.AppLanguageResourceHandler
@@ -59,21 +60,20 @@ class ResumeLessonFragmentPresenter @Inject constructor(
   fun handleOnCreate(
     inflater: LayoutInflater,
     container: ViewGroup?,
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
-    explorationCheckpoint: ExplorationCheckpoint
+    parentScreen: ExplorationActivityParams.ParentScreen,
+    checkpoint: ExplorationCheckpoint
   ): View? {
-
     binding = ResumeLessonFragmentBinding.inflate(
       inflater,
       container,
       /* attachToRoot= */ false
     )
 
-    this.profileId = ProfileId.newBuilder().setInternalId(internalProfileId).build()
+    this.profileId = profileId
     this.topicId = topicId
     this.storyId = storyId
     this.explorationId = explorationId
@@ -83,28 +83,28 @@ class ResumeLessonFragmentPresenter @Inject constructor(
       it.viewModel = resumeLessonViewModel
     }
 
-    resumeLessonViewModel.explorationCheckpoint.set(explorationCheckpoint)
+    resumeLessonViewModel.explorationCheckpoint.set(checkpoint)
     subscribeToChapterSummary()
 
     binding.resumeLessonContinueButton.setOnClickListener {
       playExploration(
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
         resumeLessonViewModel.explorationCheckpoint.get()!!,
-        backflowScreen
+        parentScreen
       )
     }
 
     binding.resumeLessonStartOverButton.setOnClickListener {
       playExploration(
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
         ExplorationCheckpoint.getDefaultInstance(),
-        backflowScreen
+        parentScreen
       )
     }
 
@@ -174,20 +174,20 @@ class ResumeLessonFragmentPresenter @Inject constructor(
   }
 
   private fun playExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
     checkpoint: ExplorationCheckpoint,
-    backflowScreen: Int?
+    parentScreen: ExplorationActivityParams.ParentScreen
   ) {
     val startPlayingProvider = if (checkpoint == ExplorationCheckpoint.getDefaultInstance()) {
       explorationDataController.restartExploration(
-        internalProfileId, topicId, storyId, explorationId
+        profileId.internalId, topicId, storyId, explorationId
       )
     } else {
       explorationDataController.resumeExploration(
-        internalProfileId, topicId, storyId, explorationId, checkpoint
+        profileId.internalId, topicId, storyId, explorationId, checkpoint
       )
     }
     startPlayingProvider.toLiveData().observe(fragment) { result ->
@@ -198,11 +198,11 @@ class ResumeLessonFragmentPresenter @Inject constructor(
         is AsyncResult.Success -> {
           oppiaLogger.d("ResumeLessonFragment", "Successfully loaded exploration")
           routeToExplorationListener.routeToExploration(
-            internalProfileId,
+            profileId,
             topicId,
             storyId,
             explorationId,
-            backflowScreen,
+            parentScreen,
             // Checkpointing is enabled be default because stating lesson from
             // ResumeLessonFragment implies that learner has not completed the lesson.
             isCheckpointingEnabled = true
diff --git a/app/src/main/java/org/oppia/android/app/story/ExplorationSelectionListener.kt b/app/src/main/java/org/oppia/android/app/story/ExplorationSelectionListener.kt
index c8667d2a992..8f42436a7c0 100644
--- a/app/src/main/java/org/oppia/android/app/story/ExplorationSelectionListener.kt
+++ b/app/src/main/java/org/oppia/android/app/story/ExplorationSelectionListener.kt
@@ -1,18 +1,20 @@
 package org.oppia.android.app.story
 
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
+import org.oppia.android.app.model.ProfileId
 
 /** Listener for cases when the user taps on a specific chapter/exploration to play. */
 interface ExplorationSelectionListener {
   /** Called when an exploration has been selected by the user. */
   fun selectExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
     canExplorationBeResumed: Boolean,
     canHavePartialProgressSaved: Boolean,
-    backflowId: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     explorationCheckpoint: ExplorationCheckpoint
   )
 }
diff --git a/app/src/main/java/org/oppia/android/app/story/StoryActivity.kt b/app/src/main/java/org/oppia/android/app/story/StoryActivity.kt
index 65fc4f809da..c02942e29d4 100644
--- a/app/src/main/java/org/oppia/android/app/story/StoryActivity.kt
+++ b/app/src/main/java/org/oppia/android/app/story/StoryActivity.kt
@@ -6,7 +6,9 @@ import android.os.Bundle
 import org.oppia.android.app.activity.ActivityComponentImpl
 import org.oppia.android.app.activity.InjectableAppCompatActivity
 import org.oppia.android.app.home.RouteToExplorationListener
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
+import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.player.exploration.ExplorationActivity
 import org.oppia.android.app.resumelesson.ResumeLessonActivity
 import org.oppia.android.app.topic.RouteToResumeLessonListener
@@ -37,42 +39,42 @@ class StoryActivity :
   }
 
   override fun routeToExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     isCheckpointingEnabled: Boolean
   ) {
     startActivity(
       ExplorationActivity.createExplorationActivityIntent(
         this,
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         isCheckpointingEnabled
       )
     )
   }
 
   override fun routeToResumeLesson(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     explorationCheckpoint: ExplorationCheckpoint
   ) {
     startActivity(
       ResumeLessonActivity.createResumeLessonActivityIntent(
         this,
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         explorationCheckpoint
       )
     )
diff --git a/app/src/main/java/org/oppia/android/app/story/StoryFragment.kt b/app/src/main/java/org/oppia/android/app/story/StoryFragment.kt
index 9d059264948..0d4187b132b 100644
--- a/app/src/main/java/org/oppia/android/app/story/StoryFragment.kt
+++ b/app/src/main/java/org/oppia/android/app/story/StoryFragment.kt
@@ -7,7 +7,9 @@ import android.view.View
 import android.view.ViewGroup
 import org.oppia.android.app.fragment.FragmentComponentImpl
 import org.oppia.android.app.fragment.InjectableFragment
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
+import org.oppia.android.app.model.ProfileId
 import org.oppia.android.util.extensions.getStringFromBundle
 import javax.inject.Inject
 
@@ -65,23 +67,23 @@ class StoryFragment : InjectableFragment(), ExplorationSelectionListener, StoryF
   }
 
   override fun selectExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
     canExplorationBeResumed: Boolean,
     canHavePartialProgressSaved: Boolean,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     explorationCheckpoint: ExplorationCheckpoint
   ) {
     storyFragmentPresenter.handleSelectExploration(
-      internalProfileId,
+      profileId,
       topicId,
       storyId,
       explorationId,
       canExplorationBeResumed,
       canHavePartialProgressSaved,
-      backflowScreen,
+      parentScreen,
       explorationCheckpoint
     )
   }
diff --git a/app/src/main/java/org/oppia/android/app/story/StoryFragmentPresenter.kt b/app/src/main/java/org/oppia/android/app/story/StoryFragmentPresenter.kt
index b1dee626bcf..ff4037415af 100644
--- a/app/src/main/java/org/oppia/android/app/story/StoryFragmentPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/story/StoryFragmentPresenter.kt
@@ -21,7 +21,9 @@ import androidx.recyclerview.widget.RecyclerView
 import org.oppia.android.R
 import org.oppia.android.app.home.RouteToExplorationListener
 import org.oppia.android.app.model.ChapterPlayState
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
+import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.recyclerview.BindableAdapter
 import org.oppia.android.app.story.storyitemviewmodel.StoryChapterSummaryViewModel
 import org.oppia.android.app.story.storyitemviewmodel.StoryHeaderViewModel
@@ -104,32 +106,32 @@ class StoryFragmentPresenter @Inject constructor(
   }
 
   fun handleSelectExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
     canExplorationBeResumed: Boolean,
     canHavePartialProgressSaved: Boolean,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     explorationCheckpoint: ExplorationCheckpoint
   ) {
     if (canExplorationBeResumed) {
       routeToResumeLessonListener.routeToResumeLesson(
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         explorationCheckpoint
       )
     } else {
       playExploration(
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
         canHavePartialProgressSaved,
-        backflowScreen
+        parentScreen
       )
     }
   }
@@ -251,22 +253,22 @@ class StoryFragmentPresenter @Inject constructor(
   }
 
   private fun playExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
     canHavePartialProgressSaved: Boolean,
-    backflowScreen: Int?
+    parentScreen: ExplorationActivityParams.ParentScreen
   ) {
     // If there's no existing progress, this is either playing a new exploration or replaying an old
     // one.
     val startPlayingProvider = if (canHavePartialProgressSaved) {
       explorationDataController.startPlayingNewExploration(
-        internalProfileId, topicId, storyId, explorationId
+        profileId.internalId, topicId, storyId, explorationId
       )
     } else {
       explorationDataController.replayExploration(
-        internalProfileId, topicId, storyId, explorationId
+        profileId.internalId, topicId, storyId, explorationId
       )
     }
     startPlayingProvider.toLiveData().observe(fragment) { result ->
@@ -277,11 +279,11 @@ class StoryFragmentPresenter @Inject constructor(
         is AsyncResult.Success -> {
           oppiaLogger.d("Story Fragment", "Successfully loaded exploration: $explorationId")
           routeToExplorationListener.routeToExploration(
-            internalProfileId,
+            profileId,
             topicId,
             storyId,
             explorationId,
-            backflowScreen,
+            parentScreen,
             isCheckpointingEnabled = canHavePartialProgressSaved
           )
         }
diff --git a/app/src/main/java/org/oppia/android/app/story/storyitemviewmodel/StoryChapterSummaryViewModel.kt b/app/src/main/java/org/oppia/android/app/story/storyitemviewmodel/StoryChapterSummaryViewModel.kt
index e5e84976d60..746af71c90b 100644
--- a/app/src/main/java/org/oppia/android/app/story/storyitemviewmodel/StoryChapterSummaryViewModel.kt
+++ b/app/src/main/java/org/oppia/android/app/story/storyitemviewmodel/StoryChapterSummaryViewModel.kt
@@ -5,6 +5,7 @@ import androidx.lifecycle.Observer
 import org.oppia.android.R
 import org.oppia.android.app.model.ChapterPlayState
 import org.oppia.android.app.model.EphemeralChapterSummary
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
 import org.oppia.android.app.model.LessonThumbnail
 import org.oppia.android.app.model.ProfileId
@@ -45,6 +46,9 @@ class StoryChapterSummaryViewModel(
     )
   }
   val chapterPlayState: ChapterPlayState = chapterSummary.chapterPlayState
+  private val profileId by lazy {
+    ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+  }
 
   fun onExplorationClicked() {
     val canHavePartialProgressSaved =
@@ -71,25 +75,25 @@ class StoryChapterSummaryViewModel(
             if (it is AsyncResult.Success) {
               explorationCheckpointLiveData.removeObserver(this)
               explorationSelectionListener.selectExploration(
-                internalProfileId,
+                profileId,
                 topicId,
                 storyId,
                 explorationId,
                 canExplorationBeResumed = true,
                 canHavePartialProgressSaved,
-                backflowId = 1,
+                parentScreen = ExplorationActivityParams.ParentScreen.STORY_SCREEN,
                 explorationCheckpoint = it.value
               )
             } else if (it is AsyncResult.Failure) {
               explorationCheckpointLiveData.removeObserver(this)
               explorationSelectionListener.selectExploration(
-                internalProfileId,
+                profileId,
                 topicId,
                 storyId,
                 explorationId,
                 canExplorationBeResumed = false,
                 canHavePartialProgressSaved,
-                backflowId = 1,
+                parentScreen = ExplorationActivityParams.ParentScreen.STORY_SCREEN,
                 explorationCheckpoint = ExplorationCheckpoint.getDefaultInstance()
               )
             }
@@ -98,13 +102,13 @@ class StoryChapterSummaryViewModel(
       )
     } else {
       explorationSelectionListener.selectExploration(
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
         canExplorationBeResumed = false,
         canHavePartialProgressSaved,
-        backflowId = 1,
+        parentScreen = ExplorationActivityParams.ParentScreen.STORY_SCREEN,
         explorationCheckpoint = ExplorationCheckpoint.getDefaultInstance()
       )
     }
diff --git a/app/src/main/java/org/oppia/android/app/testing/ExplorationTestActivity.kt b/app/src/main/java/org/oppia/android/app/testing/ExplorationTestActivity.kt
index 0eab42a60a2..8c47b60e056 100644
--- a/app/src/main/java/org/oppia/android/app/testing/ExplorationTestActivity.kt
+++ b/app/src/main/java/org/oppia/android/app/testing/ExplorationTestActivity.kt
@@ -4,6 +4,8 @@ import android.os.Bundle
 import org.oppia.android.app.activity.ActivityComponentImpl
 import org.oppia.android.app.activity.InjectableAppCompatActivity
 import org.oppia.android.app.home.RouteToExplorationListener
+import org.oppia.android.app.model.ExplorationActivityParams
+import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.player.exploration.ExplorationActivity
 import org.oppia.android.app.topic.TopicFragment
 import org.oppia.android.app.utility.SplitScreenManager
@@ -28,21 +30,21 @@ class ExplorationTestActivity : InjectableAppCompatActivity(), RouteToExploratio
   }
 
   override fun routeToExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     isCheckpointingEnabled: Boolean
   ) {
     startActivity(
       ExplorationActivity.createExplorationActivityIntent(
         this,
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         isCheckpointingEnabled
       )
     )
diff --git a/app/src/main/java/org/oppia/android/app/testing/ExplorationTestActivityPresenter.kt b/app/src/main/java/org/oppia/android/app/testing/ExplorationTestActivityPresenter.kt
index d57623b188e..f4a4285b28d 100644
--- a/app/src/main/java/org/oppia/android/app/testing/ExplorationTestActivityPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/testing/ExplorationTestActivityPresenter.kt
@@ -9,6 +9,8 @@ import org.oppia.android.app.activity.ActivityScope
 import org.oppia.android.app.fragment.FragmentComponentImpl
 import org.oppia.android.app.fragment.InjectableFragment
 import org.oppia.android.app.home.RouteToExplorationListener
+import org.oppia.android.app.model.ExplorationActivityParams
+import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.utility.SplitScreenManager
 import org.oppia.android.domain.exploration.ExplorationDataController
 import org.oppia.android.domain.oppialogger.OppiaLogger
@@ -64,11 +66,11 @@ class ExplorationTestActivityPresenter @Inject constructor(
           is AsyncResult.Success -> {
             oppiaLogger.d(TAG_EXPLORATION_TEST_ACTIVITY, "Successfully loaded exploration")
             routeToExplorationListener.routeToExploration(
-              INTERNAL_PROFILE_ID,
+              ProfileId.newBuilder().apply { internalId = INTERNAL_PROFILE_ID }.build(),
               TOPIC_ID,
               STORY_ID,
               EXPLORATION_ID,
-              backflowScreen = null,
+              parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED,
               isCheckpointingEnabled = false
             )
           }
diff --git a/app/src/main/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivity.kt b/app/src/main/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivity.kt
index b84f46c6765..7b415d9cf20 100644
--- a/app/src/main/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivity.kt
+++ b/app/src/main/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivity.kt
@@ -5,6 +5,7 @@ import android.content.Intent
 import android.os.Bundle
 import org.oppia.android.app.activity.ActivityComponentImpl
 import org.oppia.android.app.activity.InjectableAppCompatActivity
+import org.oppia.android.app.model.ReadingTextSize
 import javax.inject.Inject
 
 /** Test activity used for testing font scale. */
@@ -16,9 +17,9 @@ class TestFontScaleConfigurationUtilActivity : InjectableAppCompatActivity() {
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     (activityComponent as ActivityComponentImpl).inject(this)
-    val readingTextSize = checkNotNull(intent.getStringExtra(FONT_SCALE_EXTRA_KEY)) {
-      "Expected $FONT_SCALE_EXTRA_KEY to be in intent extras."
-    }
+    val readingTextSize = checkNotNull(
+      intent.getSerializableExtra(FONT_SCALE_EXTRA_KEY) as? ReadingTextSize
+    ) { "Expected $FONT_SCALE_EXTRA_KEY to be in intent extras." }
     configUtilActivityPresenter.handleOnCreate(readingTextSize)
   }
 
@@ -26,7 +27,7 @@ class TestFontScaleConfigurationUtilActivity : InjectableAppCompatActivity() {
     private const val FONT_SCALE_EXTRA_KEY = "TestFontScaleConfigurationUtilActivity.font_scale"
 
     /** Returns a new [TestFontScaleConfigurationUtilActivity] for context and reading text size. */
-    fun createFontScaleTestActivity(context: Context, readingTextSize: String): Intent {
+    fun createFontScaleTestActivity(context: Context, readingTextSize: ReadingTextSize): Intent {
       val intent = Intent(context, TestFontScaleConfigurationUtilActivity::class.java)
       intent.putExtra(FONT_SCALE_EXTRA_KEY, readingTextSize)
       return intent
diff --git a/app/src/main/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivityPresenter.kt b/app/src/main/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivityPresenter.kt
index c46630eb39e..b09b76d15c0 100644
--- a/app/src/main/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivityPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivityPresenter.kt
@@ -3,6 +3,7 @@ package org.oppia.android.app.testing
 import androidx.appcompat.app.AppCompatActivity
 import org.oppia.android.R
 import org.oppia.android.app.activity.ActivityScope
+import org.oppia.android.app.model.ReadingTextSize
 import org.oppia.android.app.utility.FontScaleConfigurationUtil
 import javax.inject.Inject
 
@@ -12,7 +13,7 @@ class TestFontScaleConfigurationUtilActivityPresenter @Inject constructor(
   private val activity: AppCompatActivity,
   private val fontScaleConfigurationUtil: FontScaleConfigurationUtil
 ) {
-  fun handleOnCreate(readingTextSize: String) {
+  fun handleOnCreate(readingTextSize: ReadingTextSize) {
     fontScaleConfigurationUtil.adjustFontScale(activity, readingTextSize)
     activity.setContentView(R.layout.font_scale_test_activity)
   }
diff --git a/app/src/main/java/org/oppia/android/app/testing/TopicTestActivity.kt b/app/src/main/java/org/oppia/android/app/testing/TopicTestActivity.kt
index eaa6c7a54af..292dbb8138a 100644
--- a/app/src/main/java/org/oppia/android/app/testing/TopicTestActivity.kt
+++ b/app/src/main/java/org/oppia/android/app/testing/TopicTestActivity.kt
@@ -4,6 +4,7 @@ import android.os.Bundle
 import org.oppia.android.app.activity.ActivityComponentImpl
 import org.oppia.android.app.activity.InjectableAppCompatActivity
 import org.oppia.android.app.home.RouteToExplorationListener
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.player.exploration.ExplorationActivity
 import org.oppia.android.app.story.StoryActivity
@@ -58,21 +59,21 @@ class TopicTestActivity :
   }
 
   override fun routeToExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     isCheckpointingEnabled: Boolean
   ) {
     startActivity(
       ExplorationActivity.createExplorationActivityIntent(
         this,
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         isCheckpointingEnabled
       )
     )
diff --git a/app/src/main/java/org/oppia/android/app/testing/TopicTestActivityForStory.kt b/app/src/main/java/org/oppia/android/app/testing/TopicTestActivityForStory.kt
index b055504b828..a5216c51ec2 100644
--- a/app/src/main/java/org/oppia/android/app/testing/TopicTestActivityForStory.kt
+++ b/app/src/main/java/org/oppia/android/app/testing/TopicTestActivityForStory.kt
@@ -4,6 +4,7 @@ import android.os.Bundle
 import org.oppia.android.app.activity.ActivityComponentImpl
 import org.oppia.android.app.activity.InjectableAppCompatActivity
 import org.oppia.android.app.home.RouteToExplorationListener
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
 import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.player.exploration.ExplorationActivity
@@ -63,32 +64,32 @@ class TopicTestActivityForStory :
   }
 
   override fun routeToResumeLesson(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     explorationCheckpoint: ExplorationCheckpoint
   ) {
     startActivity(
       ResumeLessonActivity.createResumeLessonActivityIntent(
         this,
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         explorationCheckpoint
       )
     )
   }
 
   override fun routeToExploration(
-    profileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     isCheckpointingEnabled: Boolean
   ) {
     startActivity(
@@ -98,7 +99,7 @@ class TopicTestActivityForStory :
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         isCheckpointingEnabled
       )
     )
diff --git a/app/src/main/java/org/oppia/android/app/topic/RouteToResumeLessonListener.kt b/app/src/main/java/org/oppia/android/app/topic/RouteToResumeLessonListener.kt
index 5a88a638dc8..babe6ff0d83 100644
--- a/app/src/main/java/org/oppia/android/app/topic/RouteToResumeLessonListener.kt
+++ b/app/src/main/java/org/oppia/android/app/topic/RouteToResumeLessonListener.kt
@@ -1,16 +1,18 @@
 package org.oppia.android.app.topic
 
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
+import org.oppia.android.app.model.ProfileId
 
 /** Listener for when an activity should route to a [ResumeLessonActivity]. */
 interface RouteToResumeLessonListener {
   /** Called selects an exploration that can be resumed. */
   fun routeToResumeLesson(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     explorationCheckpoint: ExplorationCheckpoint
   )
 }
diff --git a/app/src/main/java/org/oppia/android/app/topic/TopicActivity.kt b/app/src/main/java/org/oppia/android/app/topic/TopicActivity.kt
index d3991d3edf8..b087c05c145 100755
--- a/app/src/main/java/org/oppia/android/app/topic/TopicActivity.kt
+++ b/app/src/main/java/org/oppia/android/app/topic/TopicActivity.kt
@@ -9,6 +9,7 @@ import org.oppia.android.app.activity.ActivityIntentFactories
 import org.oppia.android.app.activity.InjectableAppCompatActivity
 import org.oppia.android.app.drawer.NAVIGATION_PROFILE_ID_ARGUMENT_KEY
 import org.oppia.android.app.home.RouteToExplorationListener
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
 import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.player.exploration.ExplorationActivity
@@ -81,42 +82,42 @@ class TopicActivity :
   }
 
   override fun routeToExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     isCheckpointingEnabled: Boolean
   ) {
     startActivity(
       ExplorationActivity.createExplorationActivityIntent(
         this,
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         isCheckpointingEnabled
       )
     )
   }
 
   override fun routeToResumeLesson(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
-    backflowScreen: Int?,
+    parentScreen: ExplorationActivityParams.ParentScreen,
     explorationCheckpoint: ExplorationCheckpoint
   ) {
     startActivity(
       ResumeLessonActivity.createResumeLessonActivityIntent(
         this,
-        internalProfileId,
+        profileId,
         topicId,
         storyId,
         explorationId,
-        backflowScreen,
+        parentScreen,
         explorationCheckpoint
       )
     )
diff --git a/app/src/main/java/org/oppia/android/app/topic/lessons/TopicLessonsFragmentPresenter.kt b/app/src/main/java/org/oppia/android/app/topic/lessons/TopicLessonsFragmentPresenter.kt
index 9336a1d7db6..55347f05b0e 100644
--- a/app/src/main/java/org/oppia/android/app/topic/lessons/TopicLessonsFragmentPresenter.kt
+++ b/app/src/main/java/org/oppia/android/app/topic/lessons/TopicLessonsFragmentPresenter.kt
@@ -10,6 +10,7 @@ import org.oppia.android.app.fragment.FragmentScope
 import org.oppia.android.app.home.RouteToExplorationListener
 import org.oppia.android.app.model.ChapterPlayState
 import org.oppia.android.app.model.ChapterSummary
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
 import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.model.StorySummary
@@ -240,6 +241,9 @@ class TopicLessonsFragmentPresenter @Inject constructor(
     explorationId: String,
     chapterPlayState: ChapterPlayState
   ) {
+    val profileId = ProfileId.newBuilder().apply {
+      internalId = internalProfileId
+    }.build()
     val canHavePartialProgressSaved =
       when (chapterPlayState) {
         ChapterPlayState.IN_PROGRESS_SAVED, ChapterPlayState.IN_PROGRESS_NOT_SAVED,
@@ -253,10 +257,7 @@ class TopicLessonsFragmentPresenter @Inject constructor(
       ChapterPlayState.IN_PROGRESS_SAVED -> {
         val explorationCheckpointLiveData =
           explorationCheckpointController.retrieveExplorationCheckpoint(
-            ProfileId.newBuilder().apply {
-              internalId = internalProfileId
-            }.build(),
-            explorationId
+            profileId, explorationId
           ).toLiveData()
         explorationCheckpointLiveData.observe(
           fragment,
@@ -265,17 +266,17 @@ class TopicLessonsFragmentPresenter @Inject constructor(
               if (it is AsyncResult.Success) {
                 explorationCheckpointLiveData.removeObserver(this)
                 routeToResumeLessonListener.routeToResumeLesson(
-                  internalProfileId,
+                  profileId,
                   topicId,
                   storyId,
                   explorationId,
-                  backflowScreen = 0,
+                  parentScreen = ExplorationActivityParams.ParentScreen.TOPIC_SCREEN_LESSONS_TAB,
                   explorationCheckpoint = it.value
                 )
               } else if (it is AsyncResult.Failure) {
                 explorationCheckpointLiveData.removeObserver(this)
                 playExploration(
-                  internalProfileId,
+                  profileId,
                   topicId,
                   storyId,
                   explorationId,
@@ -289,7 +290,7 @@ class TopicLessonsFragmentPresenter @Inject constructor(
       }
       ChapterPlayState.IN_PROGRESS_NOT_SAVED -> {
         playExploration(
-          internalProfileId,
+          profileId,
           topicId,
           storyId,
           explorationId,
@@ -299,7 +300,7 @@ class TopicLessonsFragmentPresenter @Inject constructor(
       }
       else -> {
         playExploration(
-          internalProfileId,
+          profileId,
           topicId,
           storyId,
           explorationId,
@@ -311,7 +312,7 @@ class TopicLessonsFragmentPresenter @Inject constructor(
   }
 
   private fun playExploration(
-    internalProfileId: Int,
+    profileId: ProfileId,
     topicId: String,
     storyId: String,
     explorationId: String,
@@ -348,11 +349,11 @@ class TopicLessonsFragmentPresenter @Inject constructor(
         is AsyncResult.Success -> {
           oppiaLogger.d("TopicLessonsFragment", "Successfully loaded exploration")
           routeToExplorationListener.routeToExploration(
-            internalProfileId,
+            profileId,
             topicId,
             storyId,
             explorationId,
-            backflowScreen = 0,
+            parentScreen = ExplorationActivityParams.ParentScreen.TOPIC_SCREEN_LESSONS_TAB,
             isCheckpointingEnabled = canHavePartialProgressSaved
           )
         }
diff --git a/app/src/main/java/org/oppia/android/app/utility/FontScaleConfigurationUtil.kt b/app/src/main/java/org/oppia/android/app/utility/FontScaleConfigurationUtil.kt
index f0bcf1bdb9a..78731ab1ce5 100644
--- a/app/src/main/java/org/oppia/android/app/utility/FontScaleConfigurationUtil.kt
+++ b/app/src/main/java/org/oppia/android/app/utility/FontScaleConfigurationUtil.kt
@@ -9,11 +9,11 @@ import javax.inject.Inject
 
 /** Utility to change the scale of font for the entire app. */
 class FontScaleConfigurationUtil @Inject constructor() {
-  /** This method updates font scale. */
-  fun adjustFontScale(
-    context: Context,
-    readingTextSize: String
-  ) {
+  /**
+   * Updates the specified [context]'s current configuration to scale text size according to the
+   * provided [readingTextSize].
+   */
+  fun adjustFontScale(context: Context, readingTextSize: ReadingTextSize) {
     val configuration = context.resources.configuration
     configuration.fontScale = getReadingTextSizeConfigurationUtil(readingTextSize)
     val metrics: DisplayMetrics = context.resources.displayMetrics
@@ -24,13 +24,12 @@ class FontScaleConfigurationUtil @Inject constructor() {
     context.resources.displayMetrics.setTo(metrics)
   }
 
-  /** This method returns font scale by reading text size. */
-  private fun getReadingTextSizeConfigurationUtil(readingTextSize: String): Float {
+  private fun getReadingTextSizeConfigurationUtil(readingTextSize: ReadingTextSize): Float {
     return when (readingTextSize) {
-      ReadingTextSize.SMALL_TEXT_SIZE.name -> .8f
-      ReadingTextSize.MEDIUM_TEXT_SIZE.name -> 1.0f
-      ReadingTextSize.LARGE_TEXT_SIZE.name -> 1.2f
-      ReadingTextSize.EXTRA_LARGE_TEXT_SIZE.name -> 1.4f
+      ReadingTextSize.SMALL_TEXT_SIZE -> .8f
+      ReadingTextSize.MEDIUM_TEXT_SIZE -> 1.0f
+      ReadingTextSize.LARGE_TEXT_SIZE -> 1.2f
+      ReadingTextSize.EXTRA_LARGE_TEXT_SIZE -> 1.4f
       else -> 1.0f
     }
   }
diff --git a/app/src/main/res/layout-sw600dp/option_story_text_size.xml b/app/src/main/res/layout-sw600dp/option_story_text_size.xml
index 42b3b719afd..88ad2e2a54f 100644
--- a/app/src/main/res/layout-sw600dp/option_story_text_size.xml
+++ b/app/src/main/res/layout-sw600dp/option_story_text_size.xml
@@ -45,7 +45,7 @@
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:fontFamily="sans-serif"
-      android:text="@{viewModel.readingTextSize}"
+      android:text="@{viewModel.textSizeName}"
       android:textColor="@color/component_color_option_activity_sub_heading_text_color"
       android:textSize="14sp"
       app:layout_constraintEnd_toEndOf="parent"
diff --git a/app/src/main/res/layout/option_story_text_size.xml b/app/src/main/res/layout/option_story_text_size.xml
index 076b3aeb84a..62bb2d69369 100644
--- a/app/src/main/res/layout/option_story_text_size.xml
+++ b/app/src/main/res/layout/option_story_text_size.xml
@@ -41,7 +41,7 @@
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:fontFamily="sans-serif"
-      android:text="@{viewModel.readingTextSize}"
+      android:text="@{viewModel.textSizeName}"
       android:textColor="@color/component_color_option_activity_sub_heading_text_color"
       android:textSize="14sp"
       app:layout_constraintEnd_toEndOf="parent"
diff --git a/app/src/main/res/layout/text_size_items.xml b/app/src/main/res/layout/text_size_items.xml
index 55cf9284ae8..4fe186aa4d9 100644
--- a/app/src/main/res/layout/text_size_items.xml
+++ b/app/src/main/res/layout/text_size_items.xml
@@ -14,7 +14,7 @@
     android:background="@drawable/general_item_background_border_light"
     android:gravity="center_vertical"
     android:minHeight="48dp"
-    android:onClick="@{() -> viewModel.textSizeRadioButtonListener.onTextSizeSelected(viewModel.textSizeName)}"
+    android:onClick="@{() -> viewModel.textSizeRadioButtonListener.onTextSizeSelected(viewModel.readingTextSize)}"
     android:importantForAccessibility="yes"
     android:orientation="horizontal">
 
diff --git a/app/src/sharedTest/java/org/oppia/android/app/home/RecentlyPlayedFragmentTest.kt b/app/src/sharedTest/java/org/oppia/android/app/home/RecentlyPlayedFragmentTest.kt
index fc5a5ec42ee..ebc402da273 100644
--- a/app/src/sharedTest/java/org/oppia/android/app/home/RecentlyPlayedFragmentTest.kt
+++ b/app/src/sharedTest/java/org/oppia/android/app/home/RecentlyPlayedFragmentTest.kt
@@ -28,11 +28,15 @@ import androidx.test.espresso.matcher.ViewMatchers.withText
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.rule.ActivityTestRule
 import com.google.common.truth.Truth.assertThat
+import com.google.protobuf.MessageLite
 import dagger.Component
+import org.hamcrest.Description
+import org.hamcrest.Matcher
 import org.hamcrest.Matchers.allOf
 import org.hamcrest.Matchers.containsString
 import org.hamcrest.Matchers.instanceOf
 import org.hamcrest.Matchers.not
+import org.hamcrest.TypeSafeMatcher
 import org.junit.After
 import org.junit.Before
 import org.junit.Rule
@@ -51,7 +55,10 @@ import org.oppia.android.app.devoptions.DeveloperOptionsModule
 import org.oppia.android.app.devoptions.DeveloperOptionsStarterModule
 import org.oppia.android.app.home.recentlyplayed.RecentlyPlayedActivity
 import org.oppia.android.app.home.recentlyplayed.RecentlyPlayedFragment
+import org.oppia.android.app.model.ExplorationActivityParams
+import org.oppia.android.app.model.ExplorationCheckpoint
 import org.oppia.android.app.model.ProfileId
+import org.oppia.android.app.model.ResumeLessonActivityParams
 import org.oppia.android.app.player.exploration.ExplorationActivity
 import org.oppia.android.app.player.state.itemviewmodel.SplitScreenInteractionModule
 import org.oppia.android.app.recyclerview.RecyclerViewMatcher.Companion.atPositionOnView
@@ -112,6 +119,7 @@ import org.oppia.android.testing.time.FakeOppiaClockModule
 import org.oppia.android.util.accessibility.AccessibilityTestModule
 import org.oppia.android.util.caching.AssetModule
 import org.oppia.android.util.caching.testing.CachingTestModule
+import org.oppia.android.util.extensions.getProtoExtra
 import org.oppia.android.util.gcsresource.GcsResourceModule
 import org.oppia.android.util.locale.LocaleProdModule
 import org.oppia.android.util.logging.EventLoggingConfigurationModule
@@ -822,28 +830,23 @@ class RecentlyPlayedFragmentTest {
         )
       ).perform(click())
       testCoroutineDispatchers.runCurrent()
+
+      val expectedParams = ResumeLessonActivityParams.newBuilder().apply {
+        explorationId = FRACTIONS_EXPLORATION_ID_0
+        storyId = FRACTIONS_STORY_ID_0
+        topicId = FRACTIONS_TOPIC_ID
+        profileId = ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+        parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED
+        checkpoint = ExplorationCheckpoint.newBuilder().apply {
+          explorationTitle = "What is a Fraction?"
+          explorationVersion = 85
+          pendingStateName = "Introduction"
+          timestampOfFirstCheckpoint = 102
+        }.build()
+      }.build()
       intended(
         allOf(
-          hasExtra(
-            ResumeLessonActivity.RESUME_LESSON_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY,
-            FRACTIONS_EXPLORATION_ID_0
-          ),
-          hasExtra(
-            ResumeLessonActivity.RESUME_LESSON_ACTIVITY_STORY_ID_ARGUMENT_KEY,
-            FRACTIONS_STORY_ID_0
-          ),
-          hasExtra(
-            ResumeLessonActivity.RESUME_LESSON_ACTIVITY_TOPIC_ID_ARGUMENT_KEY,
-            FRACTIONS_TOPIC_ID
-          ),
-          hasExtra(
-            ResumeLessonActivity.RESUME_LESSON_ACTIVITY_INTERNAL_PROFILE_ID_ARGUMENT_KEY,
-            internalProfileId
-          ),
-          hasExtra(
-            ResumeLessonActivity.RESUME_LESSON_ACTIVITY_BACKFLOW_SCREEN_KEY,
-            /* backflowScreen = */ null
-          ),
+          hasProtoExtra("ResumeLessonActivity.params", expectedParams),
           hasComponent(ResumeLessonActivity::class.java.name)
         )
       )
@@ -880,32 +883,18 @@ class RecentlyPlayedFragmentTest {
         )
       ).perform(click())
       testCoroutineDispatchers.runCurrent()
+
+      val expectedParams = ExplorationActivityParams.newBuilder().apply {
+        explorationId = FRACTIONS_EXPLORATION_ID_0
+        storyId = FRACTIONS_STORY_ID_0
+        topicId = FRACTIONS_TOPIC_ID
+        profileId = ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+        isCheckpointingEnabled = true
+        parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED
+      }.build()
       intended(
         allOf(
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY,
-            FRACTIONS_EXPLORATION_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_STORY_ID_ARGUMENT_KEY,
-            FRACTIONS_STORY_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_TOPIC_ID_ARGUMENT_KEY,
-            FRACTIONS_TOPIC_ID
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY,
-            internalProfileId
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_IS_CHECKPOINTING_ENABLED_KEY,
-            /* isCheckpointEnabled = */ true
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_BACKFLOW_SCREEN_KEY,
-            /* backflowScreen = */ null
-          ),
+          hasProtoExtra("ExplorationActivity.params", expectedParams),
           hasComponent(ExplorationActivity::class.java.name)
         )
       )
@@ -933,32 +922,18 @@ class RecentlyPlayedFragmentTest {
         )
       ).perform(click())
       testCoroutineDispatchers.runCurrent()
+
+      val expectedParams = ExplorationActivityParams.newBuilder().apply {
+        explorationId = FRACTIONS_EXPLORATION_ID_0
+        storyId = FRACTIONS_STORY_ID_0
+        topicId = FRACTIONS_TOPIC_ID
+        profileId = ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+        isCheckpointingEnabled = true
+        parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED
+      }.build()
       intended(
         allOf(
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY,
-            FRACTIONS_EXPLORATION_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_STORY_ID_ARGUMENT_KEY,
-            FRACTIONS_STORY_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_TOPIC_ID_ARGUMENT_KEY,
-            FRACTIONS_TOPIC_ID
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY,
-            internalProfileId
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_IS_CHECKPOINTING_ENABLED_KEY,
-            /* isCheckpointEnabled = */ true
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_BACKFLOW_SCREEN_KEY,
-            /* backflowScreen = */ null
-          ),
+          hasProtoExtra("ExplorationActivity.params", expectedParams),
           hasComponent(ExplorationActivity::class.java.name)
         )
       )
@@ -991,32 +966,18 @@ class RecentlyPlayedFragmentTest {
         )
       ).perform(click())
       testCoroutineDispatchers.runCurrent()
+
+      val expectedParams = ExplorationActivityParams.newBuilder().apply {
+        explorationId = FRACTIONS_EXPLORATION_ID_0
+        storyId = FRACTIONS_STORY_ID_0
+        topicId = FRACTIONS_TOPIC_ID
+        profileId = ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+        isCheckpointingEnabled = true
+        parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED
+      }.build()
       intended(
         allOf(
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY,
-            FRACTIONS_EXPLORATION_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_STORY_ID_ARGUMENT_KEY,
-            FRACTIONS_STORY_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_TOPIC_ID_ARGUMENT_KEY,
-            FRACTIONS_TOPIC_ID
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY,
-            internalProfileId
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_IS_CHECKPOINTING_ENABLED_KEY,
-            /* isCheckpointEnabled = */ true
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_BACKFLOW_SCREEN_KEY,
-            /* backflowScreen = */ null
-          ),
+          hasProtoExtra("ExplorationActivity.params", expectedParams),
           hasComponent(ExplorationActivity::class.java.name)
         )
       )
@@ -1475,13 +1436,27 @@ class RecentlyPlayedFragmentTest {
     }
   }
 
-  fun setUpTestFragment(activity: RecentlyPlayedActivity) {
+  private fun setUpTestFragment(activity: RecentlyPlayedActivity) {
     activity.supportFragmentManager
       .beginTransaction()
       .add(testFragment, TEST_FRAGMENT_TAG)
       .commitNow()
   }
 
+  private fun <T : MessageLite> hasProtoExtra(keyName: String, expectedProto: T): Matcher<Intent> {
+    val defaultProto = expectedProto.newBuilderForType().build()
+    return object : TypeSafeMatcher<Intent>() {
+      override fun describeTo(description: Description) {
+        description.appendText("Intent with extra: $keyName and proto value: $expectedProto")
+      }
+
+      override fun matchesSafely(intent: Intent): Boolean {
+        return intent.hasExtra(keyName) &&
+          intent.getProtoExtra(keyName, defaultProto) == expectedProto
+      }
+    }
+  }
+
   // TODO(#59): Figure out a way to reuse modules instead of needing to re-declare them.
   @Singleton
   @Component(
diff --git a/app/src/sharedTest/java/org/oppia/android/app/options/OptionsFragmentTest.kt b/app/src/sharedTest/java/org/oppia/android/app/options/OptionsFragmentTest.kt
index 40b61b95c6d..3496ad87adb 100644
--- a/app/src/sharedTest/java/org/oppia/android/app/options/OptionsFragmentTest.kt
+++ b/app/src/sharedTest/java/org/oppia/android/app/options/OptionsFragmentTest.kt
@@ -24,8 +24,12 @@ import androidx.test.espresso.matcher.ViewMatchers.withId
 import androidx.test.espresso.matcher.ViewMatchers.withText
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.rule.ActivityTestRule
+import com.google.protobuf.MessageLite
 import dagger.Component
+import org.hamcrest.Description
+import org.hamcrest.Matcher
 import org.hamcrest.Matchers.allOf
+import org.hamcrest.TypeSafeMatcher
 import org.junit.After
 import org.junit.Before
 import org.junit.Rule
@@ -42,6 +46,8 @@ import org.oppia.android.app.application.ApplicationStartupListenerModule
 import org.oppia.android.app.application.testing.TestingBuildFlavorModule
 import org.oppia.android.app.devoptions.DeveloperOptionsModule
 import org.oppia.android.app.devoptions.DeveloperOptionsStarterModule
+import org.oppia.android.app.model.ReadingTextSize
+import org.oppia.android.app.model.ReadingTextSizeActivityParams
 import org.oppia.android.app.player.state.itemviewmodel.SplitScreenInteractionModule
 import org.oppia.android.app.recyclerview.RecyclerViewMatcher.Companion.atPositionOnView
 import org.oppia.android.app.shim.ViewBindingShimModule
@@ -89,6 +95,7 @@ import org.oppia.android.testing.time.FakeOppiaClockModule
 import org.oppia.android.util.accessibility.AccessibilityTestModule
 import org.oppia.android.util.caching.AssetModule
 import org.oppia.android.util.caching.testing.CachingTestModule
+import org.oppia.android.util.extensions.getProtoExtra
 import org.oppia.android.util.gcsresource.GcsResourceModule
 import org.oppia.android.util.locale.LocaleProdModule
 import org.oppia.android.util.logging.EventLoggingConfigurationModule
@@ -425,12 +432,13 @@ class OptionsFragmentTest {
           targetViewId = R.id.reading_text_size_text_view
         )
       ).perform(click())
+
+      val expectedParams = ReadingTextSizeActivityParams.newBuilder().apply {
+        readingTextSize = ReadingTextSize.MEDIUM_TEXT_SIZE
+      }.build()
       intended(
         allOf(
-          hasExtra(
-            ReadingTextSizeActivity.getKeyReadingTextSizePreferenceSummaryValue(),
-            "Medium"
-          ),
+          hasProtoExtra("ReadingTextSizeActivity.params", expectedParams),
           hasComponent(ReadingTextSizeActivity::class.java.name)
         )
       )
@@ -453,16 +461,13 @@ class OptionsFragmentTest {
           targetViewId = R.id.reading_text_size_text_view
         )
       ).perform(click())
+
+      val expectedParams = ReadingTextSizeActivityParams.newBuilder().apply {
+        readingTextSize = ReadingTextSize.MEDIUM_TEXT_SIZE
+      }.build()
       intended(
         allOf(
-          hasExtra(
-            ReadingTextSizeActivity.getKeyReadingTextSizePreferenceTitle(),
-            READING_TEXT_SIZE
-          ),
-          hasExtra(
-            ReadingTextSizeActivity.getKeyReadingTextSizePreferenceSummaryValue(),
-            "Medium"
-          ),
+          hasProtoExtra("ReadingTextSizeActivity.params", expectedParams),
           hasComponent(ReadingTextSizeActivity::class.java.name)
         )
       )
@@ -629,6 +634,20 @@ class OptionsFragmentTest {
     testCoroutineDispatchers.runCurrent()
   }
 
+  private fun <T : MessageLite> hasProtoExtra(keyName: String, expectedProto: T): Matcher<Intent> {
+    val defaultProto = expectedProto.newBuilderForType().build()
+    return object : TypeSafeMatcher<Intent>() {
+      override fun describeTo(description: Description) {
+        description.appendText("Intent with extra: $keyName and proto value: $expectedProto")
+      }
+
+      override fun matchesSafely(intent: Intent): Boolean {
+        return intent.hasExtra(keyName) &&
+          intent.getProtoExtra(keyName, defaultProto) == expectedProto
+      }
+    }
+  }
+
   // TODO(#59): Figure out a way to reuse modules instead of needing to re-declare them.
   @Singleton
   @Component(
diff --git a/app/src/sharedTest/java/org/oppia/android/app/options/ReadingTextSizeActivityTest.kt b/app/src/sharedTest/java/org/oppia/android/app/options/ReadingTextSizeActivityTest.kt
index b4e3196e763..3b67326052c 100644
--- a/app/src/sharedTest/java/org/oppia/android/app/options/ReadingTextSizeActivityTest.kt
+++ b/app/src/sharedTest/java/org/oppia/android/app/options/ReadingTextSizeActivityTest.kt
@@ -2,7 +2,6 @@ package org.oppia.android.app.options
 
 import android.app.Application
 import android.content.Context
-import android.content.Intent
 import androidx.appcompat.app.AppCompatActivity
 import androidx.test.core.app.ApplicationProvider
 import androidx.test.ext.junit.runners.AndroidJUnit4
@@ -24,6 +23,7 @@ import org.oppia.android.app.application.ApplicationStartupListenerModule
 import org.oppia.android.app.application.testing.TestingBuildFlavorModule
 import org.oppia.android.app.devoptions.DeveloperOptionsModule
 import org.oppia.android.app.devoptions.DeveloperOptionsStarterModule
+import org.oppia.android.app.model.ReadingTextSize.MEDIUM_TEXT_SIZE
 import org.oppia.android.app.player.state.itemviewmodel.SplitScreenInteractionModule
 import org.oppia.android.app.shim.ViewBindingShimModule
 import org.oppia.android.app.topic.PracticeTabModule
@@ -102,10 +102,7 @@ class ReadingTextSizeActivityTest {
     ReadingTextSizeActivity::class.java, /* initialTouchMode= */ true, /* launchActivity= */ false
   )
 
-  @Inject
-  lateinit var context: Context
-
-  private val summaryValue = "Medium"
+  @Inject lateinit var context: Context
 
   @Before
   fun setUp() {
@@ -118,24 +115,16 @@ class ReadingTextSizeActivityTest {
 
   @Test
   fun testReadingTextSizeActivity_hasCorrectActivityLabel() {
-    activityTestRule.launchActivity(
-      createReadingTextSizeActivityIntent(
-        summaryValue
-      )
-    )
+    activityTestRule.launchActivity(createReadingTextSizeActivityIntent())
+
     val title = activityTestRule.activity.title
     // Verify that the activity label is correct as a proxy to verify TalkBack will announce the
     // correct string when it's read out.
     assertThat(title).isEqualTo(context.getString(R.string.reading_text_size_activity_title))
   }
 
-  private fun createReadingTextSizeActivityIntent(summaryValue: String): Intent {
-    return ReadingTextSizeActivity.createReadingTextSizeActivityIntent(
-      ApplicationProvider.getApplicationContext(),
-      READING_TEXT_SIZE,
-      summaryValue
-    )
-  }
+  private fun createReadingTextSizeActivityIntent() =
+    ReadingTextSizeActivity.createReadingTextSizeActivityIntent(context, MEDIUM_TEXT_SIZE)
 
   // TODO(#59): Figure out a way to reuse modules instead of needing to re-declare them.
   @Singleton
diff --git a/app/src/sharedTest/java/org/oppia/android/app/options/ReadingTextSizeFragmentTest.kt b/app/src/sharedTest/java/org/oppia/android/app/options/ReadingTextSizeFragmentTest.kt
index c0a5a36a26e..0e75dac607e 100644
--- a/app/src/sharedTest/java/org/oppia/android/app/options/ReadingTextSizeFragmentTest.kt
+++ b/app/src/sharedTest/java/org/oppia/android/app/options/ReadingTextSizeFragmentTest.kt
@@ -37,6 +37,7 @@ import org.oppia.android.app.application.ApplicationStartupListenerModule
 import org.oppia.android.app.application.testing.TestingBuildFlavorModule
 import org.oppia.android.app.devoptions.DeveloperOptionsModule
 import org.oppia.android.app.devoptions.DeveloperOptionsStarterModule
+import org.oppia.android.app.model.ReadingTextSize.SMALL_TEXT_SIZE
 import org.oppia.android.app.player.state.itemviewmodel.SplitScreenInteractionModule
 import org.oppia.android.app.recyclerview.RecyclerViewMatcher.Companion.atPositionOnView
 import org.oppia.android.app.shim.ViewBindingShimModule
@@ -153,7 +154,7 @@ class ReadingTextSizeFragmentTest {
 
   @Test
   fun testTextSize_changeTextSizeToLarge_changeConfiguration_checkTextSizeLargeIsSelected() {
-    launch<ReadingTextSizeActivity>(createReadingTextSizeActivityIntent("Small")).use {
+    launch<ReadingTextSizeActivity>(createReadingTextSizeActivityIntent()).use {
       verifyItemIsCheckedInTextSizeRecyclerView(SMALL_TEXT_SIZE_INDEX)
       clickOnTextSizeRecyclerViewItem(LARGE_TEXT_SIZE_INDEX)
       rotateToLandscape()
@@ -163,7 +164,7 @@ class ReadingTextSizeFragmentTest {
 
   @Test
   fun testTextSize_checkTextSizeOfAllFourItems_textSizeMatchedCorrectly() {
-    launch<ReadingTextSizeActivity>(createReadingTextSizeActivityIntent("Small")).use {
+    launch<ReadingTextSizeActivity>(createReadingTextSizeActivityIntent()).use {
       matchTextSizeOfTextSizeRecyclerViewItem(
         SMALL_TEXT_SIZE_INDEX, defaultTextSizeInFloat * SMALL_TEXT_SIZE_SCALE
       )
@@ -189,13 +190,8 @@ class ReadingTextSizeFragmentTest {
     }
   }
 
-  private fun createReadingTextSizeActivityIntent(summaryValue: String): Intent {
-    return ReadingTextSizeActivity.createReadingTextSizeActivityIntent(
-      ApplicationProvider.getApplicationContext(),
-      READING_TEXT_SIZE,
-      summaryValue
-    )
-  }
+  private fun createReadingTextSizeActivityIntent() =
+    ReadingTextSizeActivity.createReadingTextSizeActivityIntent(context, SMALL_TEXT_SIZE)
 
   private fun createOptionActivityIntent(
     internalProfileId: Int,
diff --git a/app/src/sharedTest/java/org/oppia/android/app/player/exploration/ExplorationActivityTest.kt b/app/src/sharedTest/java/org/oppia/android/app/player/exploration/ExplorationActivityTest.kt
index 9830902e90c..724353f1f76 100644
--- a/app/src/sharedTest/java/org/oppia/android/app/player/exploration/ExplorationActivityTest.kt
+++ b/app/src/sharedTest/java/org/oppia/android/app/player/exploration/ExplorationActivityTest.kt
@@ -69,6 +69,7 @@ import org.oppia.android.app.application.testing.TestingBuildFlavorModule
 import org.oppia.android.app.devoptions.DeveloperOptionsModule
 import org.oppia.android.app.devoptions.DeveloperOptionsStarterModule
 import org.oppia.android.app.help.HelpActivity
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.OppiaLanguage
 import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.model.WrittenTranslationLanguageSelection
@@ -1725,11 +1726,11 @@ class ExplorationActivityTest {
   ): Intent {
     return ExplorationActivity.createExplorationActivityIntent(
       ApplicationProvider.getApplicationContext(),
-      internalProfileId,
+      ProfileId.newBuilder().apply { internalId = internalProfileId }.build(),
       topicId,
       storyId,
       explorationId,
-      /* backflowScreen= */ null,
+      parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED,
       shouldSavePartialProgress
     )
   }
diff --git a/app/src/sharedTest/java/org/oppia/android/app/resumelesson/ResumeLessonActivityTest.kt b/app/src/sharedTest/java/org/oppia/android/app/resumelesson/ResumeLessonActivityTest.kt
index e39f45da2b8..8fca32d6d39 100644
--- a/app/src/sharedTest/java/org/oppia/android/app/resumelesson/ResumeLessonActivityTest.kt
+++ b/app/src/sharedTest/java/org/oppia/android/app/resumelesson/ResumeLessonActivityTest.kt
@@ -37,7 +37,9 @@ import org.oppia.android.app.application.ApplicationStartupListenerModule
 import org.oppia.android.app.application.testing.TestingBuildFlavorModule
 import org.oppia.android.app.devoptions.DeveloperOptionsModule
 import org.oppia.android.app.devoptions.DeveloperOptionsStarterModule
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
+import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.player.state.itemviewmodel.SplitScreenInteractionModule
 import org.oppia.android.app.shim.ViewBindingShimModule
 import org.oppia.android.app.topic.PracticeTabModule
@@ -113,8 +115,6 @@ class ResumeLessonActivityTest {
   @get:Rule
   val initializeDefaultLocaleRule = InitializeDefaultLocaleRule()
 
-  private val internalProfileId: Int = 1
-
   @Inject
   lateinit var testCoroutineDispatchers: TestCoroutineDispatchers
 
@@ -192,12 +192,12 @@ class ResumeLessonActivityTest {
   private fun createResumeLessonActivityIntent(): Intent {
     return ResumeLessonActivity.createResumeLessonActivityIntent(
       context,
-      internalProfileId,
+      ProfileId.newBuilder().apply { internalId = 1 }.build(),
       FRACTIONS_TOPIC_ID,
       FRACTIONS_STORY_ID_0,
       FRACTIONS_EXPLORATION_ID_0,
-      backflowScreen = null,
-      explorationCheckpoint = ExplorationCheckpoint.getDefaultInstance()
+      parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED,
+      checkpoint = ExplorationCheckpoint.getDefaultInstance()
     )
   }
 
diff --git a/app/src/sharedTest/java/org/oppia/android/app/resumelesson/ResumeLessonFragmentTest.kt b/app/src/sharedTest/java/org/oppia/android/app/resumelesson/ResumeLessonFragmentTest.kt
index 6fe742fa7df..c0b2d3f5698 100644
--- a/app/src/sharedTest/java/org/oppia/android/app/resumelesson/ResumeLessonFragmentTest.kt
+++ b/app/src/sharedTest/java/org/oppia/android/app/resumelesson/ResumeLessonFragmentTest.kt
@@ -36,7 +36,9 @@ import org.oppia.android.app.application.ApplicationStartupListenerModule
 import org.oppia.android.app.application.testing.TestingBuildFlavorModule
 import org.oppia.android.app.devoptions.DeveloperOptionsModule
 import org.oppia.android.app.devoptions.DeveloperOptionsStarterModule
+import org.oppia.android.app.model.ExplorationActivityParams
 import org.oppia.android.app.model.ExplorationCheckpoint
+import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.player.state.itemviewmodel.SplitScreenInteractionModule
 import org.oppia.android.app.shim.ViewBindingShimModule
 import org.oppia.android.app.topic.PracticeTabModule
@@ -116,8 +118,6 @@ class ResumeLessonFragmentTest {
   @get:Rule
   val initializeDefaultLocaleRule = InitializeDefaultLocaleRule()
 
-  private val internalProfileId: Int = 1
-
   @Inject
   lateinit var testCoroutineDispatchers: TestCoroutineDispatchers
 
@@ -269,24 +269,24 @@ class ResumeLessonFragmentTest {
   private fun createResumeLessonActivityIntent(): Intent {
     return ResumeLessonActivity.createResumeLessonActivityIntent(
       context,
-      internalProfileId,
+      ProfileId.newBuilder().apply { internalId = 1 }.build(),
       FRACTIONS_TOPIC_ID,
       FRACTIONS_STORY_ID_0,
       FRACTIONS_EXPLORATION_ID_0,
-      backflowScreen = null,
-      explorationCheckpoint = ExplorationCheckpoint.getDefaultInstance()
+      parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED,
+      checkpoint = ExplorationCheckpoint.getDefaultInstance()
     )
   }
 
   private fun createResumeRatiosLessonActivityIntent(): Intent {
     return ResumeLessonActivity.createResumeLessonActivityIntent(
       context,
-      internalProfileId,
+      ProfileId.newBuilder().apply { internalId = 1 }.build(),
       RATIOS_TOPIC_ID,
       RATIOS_STORY_ID_0,
       RATIOS_EXPLORATION_ID_0,
-      backflowScreen = null,
-      explorationCheckpoint = ExplorationCheckpoint.getDefaultInstance()
+      parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED,
+      checkpoint = ExplorationCheckpoint.getDefaultInstance()
     )
   }
 
diff --git a/app/src/sharedTest/java/org/oppia/android/app/story/StoryActivityTest.kt b/app/src/sharedTest/java/org/oppia/android/app/story/StoryActivityTest.kt
index 0183b1740a5..0a0b70162bc 100644
--- a/app/src/sharedTest/java/org/oppia/android/app/story/StoryActivityTest.kt
+++ b/app/src/sharedTest/java/org/oppia/android/app/story/StoryActivityTest.kt
@@ -19,8 +19,12 @@ import androidx.test.espresso.matcher.ViewMatchers.withId
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.rule.ActivityTestRule
 import com.google.common.truth.Truth.assertThat
+import com.google.protobuf.MessageLite
 import dagger.Component
-import org.hamcrest.CoreMatchers.allOf
+import org.hamcrest.Description
+import org.hamcrest.Matcher
+import org.hamcrest.Matchers.allOf
+import org.hamcrest.TypeSafeMatcher
 import org.junit.After
 import org.junit.Before
 import org.junit.Rule
@@ -37,6 +41,8 @@ import org.oppia.android.app.application.ApplicationStartupListenerModule
 import org.oppia.android.app.application.testing.TestingBuildFlavorModule
 import org.oppia.android.app.devoptions.DeveloperOptionsModule
 import org.oppia.android.app.devoptions.DeveloperOptionsStarterModule
+import org.oppia.android.app.model.ExplorationActivityParams
+import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.player.exploration.ExplorationActivity
 import org.oppia.android.app.player.state.itemviewmodel.SplitScreenInteractionModule
 import org.oppia.android.app.shim.ViewBindingShimModule
@@ -87,6 +93,7 @@ import org.oppia.android.testing.time.FakeOppiaClockModule
 import org.oppia.android.util.accessibility.AccessibilityTestModule
 import org.oppia.android.util.caching.AssetModule
 import org.oppia.android.util.caching.testing.CachingTestModule
+import org.oppia.android.util.extensions.getProtoExtra
 import org.oppia.android.util.gcsresource.GcsResourceModule
 import org.oppia.android.util.locale.LocaleProdModule
 import org.oppia.android.util.logging.EventLoggingConfigurationModule
@@ -182,12 +189,17 @@ class StoryActivityTest {
       )
       testCoroutineDispatchers.runCurrent()
 
+      val expectedParams = ExplorationActivityParams.newBuilder().apply {
+        explorationId = TEST_EXPLORATION_ID_2
+        storyId = TEST_STORY_ID_0
+        topicId = TEST_TOPIC_ID_0
+        profileId = ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+        parentScreen = ExplorationActivityParams.ParentScreen.STORY_SCREEN
+        isCheckpointingEnabled = true
+      }.build()
       intended(
         allOf(
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY,
-            TEST_EXPLORATION_ID_2
-          ),
+          hasProtoExtra("ExplorationActivity.params", expectedParams),
           hasComponent(ExplorationActivity::class.java.name)
         )
       )
@@ -211,6 +223,20 @@ class StoryActivityTest {
     )
   }
 
+  private fun <T : MessageLite> hasProtoExtra(keyName: String, expectedProto: T): Matcher<Intent> {
+    val defaultProto = expectedProto.newBuilderForType().build()
+    return object : TypeSafeMatcher<Intent>() {
+      override fun describeTo(description: Description) {
+        description.appendText("Intent with extra: $keyName and proto value: $expectedProto")
+      }
+
+      override fun matchesSafely(intent: Intent): Boolean {
+        return intent.hasExtra(keyName) &&
+          intent.getProtoExtra(keyName, defaultProto) == expectedProto
+      }
+    }
+  }
+
   // TODO(#59): Figure out a way to reuse modules instead of needing to re-declare them.
   @Singleton
   @Component(
diff --git a/app/src/sharedTest/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivityTest.kt b/app/src/sharedTest/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivityTest.kt
index 5516365c6dd..acdf99c0863 100644
--- a/app/src/sharedTest/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivityTest.kt
+++ b/app/src/sharedTest/java/org/oppia/android/app/testing/TestFontScaleConfigurationUtilActivityTest.kt
@@ -115,7 +115,7 @@ class TestFontScaleConfigurationUtilActivityTest {
     Intents.release()
   }
 
-  private fun createFontScaleTestActivityIntent(readingTextSize: String): Intent {
+  private fun createFontScaleTestActivityIntent(readingTextSize: ReadingTextSize): Intent {
     return TestFontScaleConfigurationUtilActivity.createFontScaleTestActivity(
       context,
       readingTextSize
@@ -125,7 +125,7 @@ class TestFontScaleConfigurationUtilActivityTest {
   @Test
   fun testFontScaleConfigurationUtil_smallTextSize_hasCorrectDimension() {
     launch<TestFontScaleConfigurationUtilActivity>(
-      createFontScaleTestActivityIntent(ReadingTextSize.SMALL_TEXT_SIZE.name)
+      createFontScaleTestActivityIntent(ReadingTextSize.SMALL_TEXT_SIZE)
     ).use {
       onView(withId(R.id.font_scale_content_text_view)).check(
         matches(
@@ -140,7 +140,7 @@ class TestFontScaleConfigurationUtilActivityTest {
   @Test
   fun testFontScaleConfigurationUtil_mediumTextSize_hasCorrectDimension() {
     launch<TestFontScaleConfigurationUtilActivity>(
-      createFontScaleTestActivityIntent(ReadingTextSize.MEDIUM_TEXT_SIZE.name)
+      createFontScaleTestActivityIntent(ReadingTextSize.MEDIUM_TEXT_SIZE)
     ).use {
       onView(withId(R.id.font_scale_content_text_view)).check(
         matches(
@@ -155,7 +155,7 @@ class TestFontScaleConfigurationUtilActivityTest {
   @Test
   fun testFontScaleConfigurationUtil_largeTextSize_hasCorrectDimension() {
     launch<TestFontScaleConfigurationUtilActivity>(
-      createFontScaleTestActivityIntent(ReadingTextSize.LARGE_TEXT_SIZE.name)
+      createFontScaleTestActivityIntent(ReadingTextSize.LARGE_TEXT_SIZE)
     ).use {
       onView(withId(R.id.font_scale_content_text_view)).check(
         matches(
@@ -170,7 +170,7 @@ class TestFontScaleConfigurationUtilActivityTest {
   @Test
   fun testFontScaleConfigurationUtil_extraLargeTextSize_hasCorrectDimension() {
     launch<TestFontScaleConfigurationUtilActivity>(
-      createFontScaleTestActivityIntent(ReadingTextSize.EXTRA_LARGE_TEXT_SIZE.name)
+      createFontScaleTestActivityIntent(ReadingTextSize.EXTRA_LARGE_TEXT_SIZE)
     ).use {
       onView(withId(R.id.font_scale_content_text_view)).check(
         matches(
diff --git a/app/src/sharedTest/java/org/oppia/android/app/topic/lessons/TopicLessonsFragmentTest.kt b/app/src/sharedTest/java/org/oppia/android/app/topic/lessons/TopicLessonsFragmentTest.kt
index 9bd4ceb03eb..365674d6a51 100644
--- a/app/src/sharedTest/java/org/oppia/android/app/topic/lessons/TopicLessonsFragmentTest.kt
+++ b/app/src/sharedTest/java/org/oppia/android/app/topic/lessons/TopicLessonsFragmentTest.kt
@@ -26,10 +26,14 @@ import androidx.test.espresso.matcher.ViewMatchers.withContentDescription
 import androidx.test.espresso.matcher.ViewMatchers.withId
 import androidx.test.espresso.matcher.ViewMatchers.withText
 import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.google.protobuf.MessageLite
 import dagger.Component
+import org.hamcrest.Description
+import org.hamcrest.Matcher
 import org.hamcrest.Matchers.allOf
 import org.hamcrest.Matchers.containsString
 import org.hamcrest.Matchers.not
+import org.hamcrest.TypeSafeMatcher
 import org.junit.After
 import org.junit.Before
 import org.junit.Rule
@@ -46,7 +50,10 @@ import org.oppia.android.app.application.ApplicationStartupListenerModule
 import org.oppia.android.app.application.testing.TestingBuildFlavorModule
 import org.oppia.android.app.devoptions.DeveloperOptionsModule
 import org.oppia.android.app.devoptions.DeveloperOptionsStarterModule
+import org.oppia.android.app.model.ExplorationActivityParams
+import org.oppia.android.app.model.ExplorationCheckpoint
 import org.oppia.android.app.model.ProfileId
+import org.oppia.android.app.model.ResumeLessonActivityParams
 import org.oppia.android.app.player.exploration.ExplorationActivity
 import org.oppia.android.app.player.state.itemviewmodel.SplitScreenInteractionModule
 import org.oppia.android.app.recyclerview.RecyclerViewMatcher.Companion.atPosition
@@ -112,6 +119,7 @@ import org.oppia.android.util.accessibility.AccessibilityTestModule
 import org.oppia.android.util.accessibility.FakeAccessibilityService
 import org.oppia.android.util.caching.AssetModule
 import org.oppia.android.util.caching.testing.CachingTestModule
+import org.oppia.android.util.extensions.getProtoExtra
 import org.oppia.android.util.gcsresource.GcsResourceModule
 import org.oppia.android.util.locale.LocaleProdModule
 import org.oppia.android.util.logging.EventLoggingConfigurationModule
@@ -371,29 +379,24 @@ class TopicLessonsFragmentTest {
         )
       ).check(matches(hasDescendant(withId(R.id.chapter_container)))).perform(click())
       testCoroutineDispatchers.runCurrent()
-      intended(hasComponent(ResumeLessonActivity::class.java.name))
-      intended(
-        hasExtra(
-          ResumeLessonActivity.RESUME_LESSON_ACTIVITY_INTERNAL_PROFILE_ID_ARGUMENT_KEY,
-          internalProfileId
-        )
-      )
-      intended(
-        hasExtra(
-          ResumeLessonActivity.RESUME_LESSON_ACTIVITY_TOPIC_ID_ARGUMENT_KEY,
-          FRACTIONS_TOPIC_ID
-        )
-      )
-      intended(
-        hasExtra(
-          ResumeLessonActivity.RESUME_LESSON_ACTIVITY_STORY_ID_ARGUMENT_KEY,
-          FRACTIONS_STORY_ID_0
-        )
-      )
+
+      val expectedParams = ResumeLessonActivityParams.newBuilder().apply {
+        explorationId = FRACTIONS_EXPLORATION_ID_0
+        storyId = FRACTIONS_STORY_ID_0
+        topicId = FRACTIONS_TOPIC_ID
+        profileId = ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+        parentScreen = ExplorationActivityParams.ParentScreen.TOPIC_SCREEN_LESSONS_TAB
+        checkpoint = ExplorationCheckpoint.newBuilder().apply {
+          explorationTitle = "What is a Fraction?"
+          explorationVersion = 85
+          pendingStateName = "Introduction"
+          timestampOfFirstCheckpoint = 102
+        }.build()
+      }.build()
       intended(
-        hasExtra(
-          ResumeLessonActivity.RESUME_LESSON_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY,
-          FRACTIONS_EXPLORATION_ID_0
+        allOf(
+          hasProtoExtra("ResumeLessonActivity.params", expectedParams),
+          hasComponent(ResumeLessonActivity::class.java.name)
         )
       )
     }
@@ -422,32 +425,18 @@ class TopicLessonsFragmentTest {
         )
       ).check(matches(hasDescendant(withId(R.id.chapter_container)))).perform(click())
       testCoroutineDispatchers.runCurrent()
+
+      val expectedParams = ExplorationActivityParams.newBuilder().apply {
+        explorationId = FRACTIONS_EXPLORATION_ID_0
+        storyId = FRACTIONS_STORY_ID_0
+        topicId = FRACTIONS_TOPIC_ID
+        profileId = ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+        isCheckpointingEnabled = true
+        parentScreen = ExplorationActivityParams.ParentScreen.TOPIC_SCREEN_LESSONS_TAB
+      }.build()
       intended(
         allOf(
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY,
-            FRACTIONS_EXPLORATION_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_STORY_ID_ARGUMENT_KEY,
-            FRACTIONS_STORY_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_TOPIC_ID_ARGUMENT_KEY,
-            FRACTIONS_TOPIC_ID
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY,
-            internalProfileId
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_IS_CHECKPOINTING_ENABLED_KEY,
-            /* isCheckpointEnabled = */ true
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_BACKFLOW_SCREEN_KEY,
-            /* backflowScreen = */ 0
-          ),
+          hasProtoExtra("ExplorationActivity.params", expectedParams),
           hasComponent(ExplorationActivity::class.java.name)
         )
       )
@@ -468,32 +457,18 @@ class TopicLessonsFragmentTest {
         )
       ).check(matches(hasDescendant(withId(R.id.chapter_container)))).perform(click())
       testCoroutineDispatchers.runCurrent()
+
+      val expectedParams = ExplorationActivityParams.newBuilder().apply {
+        explorationId = FRACTIONS_EXPLORATION_ID_0
+        storyId = FRACTIONS_STORY_ID_0
+        topicId = FRACTIONS_TOPIC_ID
+        profileId = ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+        isCheckpointingEnabled = true
+        parentScreen = ExplorationActivityParams.ParentScreen.TOPIC_SCREEN_LESSONS_TAB
+      }.build()
       intended(
         allOf(
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY,
-            FRACTIONS_EXPLORATION_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_STORY_ID_ARGUMENT_KEY,
-            FRACTIONS_STORY_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_TOPIC_ID_ARGUMENT_KEY,
-            FRACTIONS_TOPIC_ID
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY,
-            internalProfileId
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_IS_CHECKPOINTING_ENABLED_KEY,
-            /* isCheckpointEnabled = */ true
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_BACKFLOW_SCREEN_KEY,
-            /* backflowScreen = */ 0
-          ),
+          hasProtoExtra("ExplorationActivity.params", expectedParams),
           hasComponent(ExplorationActivity::class.java.name)
         )
       )
@@ -519,32 +494,18 @@ class TopicLessonsFragmentTest {
         )
       ).check(matches(hasDescendant(withId(R.id.chapter_container)))).perform(click())
       testCoroutineDispatchers.runCurrent()
+
+      val expectedParams = ExplorationActivityParams.newBuilder().apply {
+        explorationId = FRACTIONS_EXPLORATION_ID_0
+        storyId = FRACTIONS_STORY_ID_0
+        topicId = FRACTIONS_TOPIC_ID
+        profileId = ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+        isCheckpointingEnabled = true
+        parentScreen = ExplorationActivityParams.ParentScreen.TOPIC_SCREEN_LESSONS_TAB
+      }.build()
       intended(
         allOf(
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY,
-            FRACTIONS_EXPLORATION_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_STORY_ID_ARGUMENT_KEY,
-            FRACTIONS_STORY_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_TOPIC_ID_ARGUMENT_KEY,
-            FRACTIONS_TOPIC_ID
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY,
-            internalProfileId
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_IS_CHECKPOINTING_ENABLED_KEY,
-            /* isCheckpointEnabled = */ true
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_BACKFLOW_SCREEN_KEY,
-            /* backflowScreen = */ 0
-          ),
+          hasProtoExtra("ExplorationActivity.params", expectedParams),
           hasComponent(ExplorationActivity::class.java.name)
         )
       )
@@ -570,32 +531,18 @@ class TopicLessonsFragmentTest {
         )
       ).check(matches(hasDescendant(withId(R.id.chapter_container)))).perform(click())
       testCoroutineDispatchers.runCurrent()
+
+      val expectedParams = ExplorationActivityParams.newBuilder().apply {
+        explorationId = FRACTIONS_EXPLORATION_ID_0
+        storyId = FRACTIONS_STORY_ID_0
+        topicId = FRACTIONS_TOPIC_ID
+        profileId = ProfileId.newBuilder().apply { internalId = internalProfileId }.build()
+        isCheckpointingEnabled = false
+        parentScreen = ExplorationActivityParams.ParentScreen.TOPIC_SCREEN_LESSONS_TAB
+      }.build()
       intended(
         allOf(
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_EXPLORATION_ID_ARGUMENT_KEY,
-            FRACTIONS_EXPLORATION_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_STORY_ID_ARGUMENT_KEY,
-            FRACTIONS_STORY_ID_0
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_TOPIC_ID_ARGUMENT_KEY,
-            FRACTIONS_TOPIC_ID
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_PROFILE_ID_ARGUMENT_KEY,
-            internalProfileId
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_IS_CHECKPOINTING_ENABLED_KEY,
-            /* isCheckpointEnabled = */ false
-          ),
-          hasExtra(
-            ExplorationActivity.EXPLORATION_ACTIVITY_BACKFLOW_SCREEN_KEY,
-            /* backflowScreen = */ 0
-          ),
+          hasProtoExtra("ExplorationActivity.params", expectedParams),
           hasComponent(ExplorationActivity::class.java.name)
         )
       )
@@ -996,6 +943,20 @@ class TopicLessonsFragmentTest {
     ).check(matches(withDrawable(R.drawable.ic_check_24dp)))
   }
 
+  private fun <T : MessageLite> hasProtoExtra(keyName: String, expectedProto: T): Matcher<Intent> {
+    val defaultProto = expectedProto.newBuilderForType().build()
+    return object : TypeSafeMatcher<Intent>() {
+      override fun describeTo(description: Description) {
+        description.appendText("Intent with extra: $keyName and proto value: $expectedProto")
+      }
+
+      override fun matchesSafely(intent: Intent): Boolean {
+        return intent.hasExtra(keyName) &&
+          intent.getProtoExtra(keyName, defaultProto) == expectedProto
+      }
+    }
+  }
+
   // TODO(#59): Figure out a way to reuse modules instead of needing to re-declare them.
   @Singleton
   @Component(
diff --git a/app/src/test/java/org/oppia/android/app/player/exploration/ExplorationActivityLocalTest.kt b/app/src/test/java/org/oppia/android/app/player/exploration/ExplorationActivityLocalTest.kt
index 84d0d72c555..8b66c19ce27 100644
--- a/app/src/test/java/org/oppia/android/app/player/exploration/ExplorationActivityLocalTest.kt
+++ b/app/src/test/java/org/oppia/android/app/player/exploration/ExplorationActivityLocalTest.kt
@@ -25,6 +25,8 @@ import org.oppia.android.app.devoptions.DeveloperOptionsModule
 import org.oppia.android.app.devoptions.DeveloperOptionsStarterModule
 import org.oppia.android.app.model.EventLog
 import org.oppia.android.app.model.EventLog.Context.ActivityContextCase.OPEN_EXPLORATION_ACTIVITY
+import org.oppia.android.app.model.ExplorationActivityParams
+import org.oppia.android.app.model.ProfileId
 import org.oppia.android.app.player.state.itemviewmodel.SplitScreenInteractionModule
 import org.oppia.android.app.shim.IntentFactoryShimModule
 import org.oppia.android.app.shim.ViewBindingShimModule
@@ -178,11 +180,11 @@ class ExplorationActivityLocalTest {
   ): Intent {
     return ExplorationActivity.createExplorationActivityIntent(
       ApplicationProvider.getApplicationContext(),
-      internalProfileId,
+      ProfileId.newBuilder().apply { internalId = internalProfileId }.build(),
       topicId,
       storyId,
       explorationId,
-      backflowScreen = null,
+      parentScreen = ExplorationActivityParams.ParentScreen.PARENT_SCREEN_UNSPECIFIED,
       isCheckpointingEnabled = false
     )
   }
diff --git a/model/src/main/proto/BUILD.bazel b/model/src/main/proto/BUILD.bazel
index 94372b448ff..51ac9b50795 100644
--- a/model/src/main/proto/BUILD.bazel
+++ b/model/src/main/proto/BUILD.bazel
@@ -27,7 +27,9 @@ oppia_proto_library(
     name = "arguments_proto",
     srcs = ["arguments.proto"],
     deps = [
+        ":exploration_checkpoint_proto",
         ":exploration_proto",
+        ":profile_proto",
         ":translation_proto",
     ],
 )
diff --git a/model/src/main/proto/arguments.proto b/model/src/main/proto/arguments.proto
index b32af37c70e..2e07098faf0 100644
--- a/model/src/main/proto/arguments.proto
+++ b/model/src/main/proto/arguments.proto
@@ -3,6 +3,8 @@ syntax = "proto3";
 package model;
 
 import "exploration.proto";
+import "exploration_checkpoint.proto";
+import "profile.proto";
 import "translation.proto";
 
 option java_package = "org.oppia.android.app.model";
@@ -64,6 +66,129 @@ message InputInteractionViewTestActivityParams {
   }
 }
 
+// Params required when creating a new ExplorationActivity.
+message ExplorationActivityParams {
+  // The ID of the profile that wants to start an exploration play session.
+  ProfileId profile_id = 1;
+
+  // The ID of the topic to which the opening exploration belongs.
+  string topic_id = 2;
+
+  // The ID of the story to which the opening exploration belongs.
+  string story_id = 3;
+
+  // The exploration being opened for a new play session.
+  string exploration_id = 4;
+
+  // The screen from which this activity was opened.
+  ParentScreen parent_screen = 5;
+
+  // Indicates whether checkpointing is enabled to story partial completion state for this session.
+  bool is_checkpointing_enabled = 6;
+
+  // Different parent screens that can open a new exploration activity instance.
+  enum ParentScreen {
+    // Indicates that the originating screen isn't actually known.
+    PARENT_SCREEN_UNSPECIFIED = 0;
+
+    // Corresponds to the lessons tab on the topic viewer screen.
+    TOPIC_SCREEN_LESSONS_TAB = 1;
+
+    // Corresponds to the story viewer screen.
+    STORY_SCREEN = 2;
+  }
+}
+
+// Arguments that must be passed to a new ExplorationFragment.
+message ExplorationFragmentArguments {
+  // The ID of the profile that wants to start an exploration play session.
+  ProfileId profile_id = 1;
+
+  // The ID of the topic to which the opening exploration belongs.
+  string topic_id = 2;
+
+  // The ID of the story to which the opening exploration belongs.
+  string story_id = 3;
+
+  // The exploration being opened for a new play session.
+  string exploration_id = 4;
+
+  // The text size at which content in the exploration should be rendered.
+  ReadingTextSize reading_text_size = 5;
+}
+
+// Params required when creating a new ResumeLessonActivity.
+message ResumeLessonActivityParams {
+  // The ID of the profile that wants to start an exploration play session.
+  ProfileId profile_id = 1;
+
+  // The ID of the topic to which the opening exploration belongs.
+  string topic_id = 2;
+
+  // The ID of the story to which the opening exploration belongs.
+  string story_id = 3;
+
+  // The exploration being opened for a new play session.
+  string exploration_id = 4;
+
+  // The screen from which this activity was opened.
+  ExplorationActivityParams.ParentScreen parent_screen = 5;
+
+  // The checkpoint that may be used to resume the exploration play session.
+  ExplorationCheckpoint checkpoint = 6;
+}
+
+// Arguments that must be passed to a new ResumeLessonFragment.
+message ResumeLessonFragmentArguments {
+  // The ID of the profile that wants to start an exploration play session.
+  ProfileId profile_id = 1;
+
+  // The ID of the topic to which the opening exploration belongs.
+  string topic_id = 2;
+
+  // The ID of the story to which the opening exploration belongs.
+  string story_id = 3;
+
+  // The exploration being opened for a new play session.
+  string exploration_id = 4;
+
+  // The screen from which this activity was opened.
+  ExplorationActivityParams.ParentScreen parent_screen = 5;
+
+  // The checkpoint that may be used to resume the exploration play session.
+  ExplorationCheckpoint checkpoint = 6;
+}
+
+// Params required when creating a new ReadingTextSizeActivity.
+message ReadingTextSizeActivityParams {
+  // The ReadingTextSize previously selected by the user (upon opening the activity).
+  ReadingTextSize reading_text_size = 1;
+}
+
+// The bundle of properties that are saved upon configuration changes in ReadingTextSizeActivity.
+message ReadingTextSizeActivityStateBundle {
+  // The ReadingTextSize selected by the user.
+  ReadingTextSize selected_reading_text_size = 1;
+}
+
+// The bundle of properties that are returned by ReadingTextSizeActivity after it's finished.
+message ReadingTextSizeActivityResultBundle {
+  // The ReadingTextSize selected by the user.
+  ReadingTextSize selected_reading_text_size = 1;
+}
+
+// Arguments required when creating a new ReadingTextSizeFragment.
+message ReadingTextSizeFragmentArguments {
+  // The ReadingTextSize previously selected by the user (upon opening the fragment).
+  ReadingTextSize reading_text_size = 1;
+}
+
+// The bundle of properties that are saved upon configuration changes in ReadingTextSizeFragment.
+message ReadingTextSizeFragmentStateBundle {
+  // The ReadingTextSize selected by the user.
+  ReadingTextSize selected_reading_text_size = 1;
+}
+
 // Activity Parameters needed to open the policy page.
 message PoliciesActivityParams {
   // The specific policy page that should be displayed.
diff --git a/scripts/assets/kdoc_validity_exemptions.textproto b/scripts/assets/kdoc_validity_exemptions.textproto
index eb430e59c77..189547e027f 100644
--- a/scripts/assets/kdoc_validity_exemptions.textproto
+++ b/scripts/assets/kdoc_validity_exemptions.textproto
@@ -134,7 +134,6 @@ exempted_file_path: "app/src/main/java/org/oppia/android/app/options/LanguageRad
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/LanguageSelectionViewModel.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/LoadAppLanguageListListener.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/LoadAudioLanguageListListener.kt"
-exempted_file_path: "app/src/main/java/org/oppia/android/app/options/LoadReadingTextSizeListener.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/OptionControlsViewModel.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/OptionsActivity.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/OptionsActivityPresenter.kt"
@@ -144,16 +143,13 @@ exempted_file_path: "app/src/main/java/org/oppia/android/app/options/OptionsFrag
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/OptionsFragmentPresenter.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/OptionsItemViewModel.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/OptionsReadingTextSizeViewModel.kt"
-exempted_file_path: "app/src/main/java/org/oppia/android/app/options/ReadingTextSizeActivity.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/ReadingTextSizeActivityPresenter.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/ReadingTextSizeFragment.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/ReadingTextSizeFragmentPresenter.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/ReadingTextSizeSelectionViewModel.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/RouteToAppLanguageListListener.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/RouteToAudioLanguageListListener.kt"
-exempted_file_path: "app/src/main/java/org/oppia/android/app/options/RouteToReadingTextSizeListener.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/options/TextSizeItemViewModel.kt"
-exempted_file_path: "app/src/main/java/org/oppia/android/app/options/TextSizeRadioButtonListener.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/parser/StringToNumberParser.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/parser/StringToRatioParser.kt"
 exempted_file_path: "app/src/main/java/org/oppia/android/app/player/audio/AudioFragmentPresenter.kt"