Authentic Lessons for 21st Century Learning

Who Bleached My Coral?

Photosynthesis and Coral Reef Health

Heather Shaffery, Laura Halstied, Brian Kennedy | Published: October 28th, 2022 by K20 Center

  • Grade Level Grade Level 6th, 7th, 8th
  • Subject Subject Science
  • Course Course
  • Time Frame Time Frame 160 minutes
  • Duration More 3-4 class periods


This lesson examines the phenomenon of coral bleaching as a context for learning about photosynthesis. Students investigate photosynthesis' inputs and outputs using an online simulation activity and connect these elements to the relationship between coral and their symbiotic algae. Student will also gather information about environmental factors that disturb coral and photosynthesis in coral reefs. Then, they will write an evidence-based explanation for a bleaching event that occurred at the Flower Garden Banks National Marine Sanctuary.

Essential Question(s)

How do photosynthesis and the relationship between coral and their symbiotic algae explain coral bleaching?



Students look at pictures to compare healthy and bleached coral. Then, students discuss possible causes of such changes to the coral reef ecosystem.


Students investigate the inputs and outputs of photosynthesis through a simulation activity.


Students make connections between photosynthesis and coral survival and create a list of environmental factors that would disturb coral and/or photosynthesis.


Students research several causes of coral bleaching that also impact photosynthesis.


Students write an evidence-based explanation for a coral bleaching event in the Flower Garden Banks National Marine Sanctuary and complete a self-reflection on their learning.


  • Lesson Slides (attached)

  • Coral Bleaching Station cards (attached; one set)

  • Coral Bleaching Graphic Organizer handout (attached; one per student)

  • Flower Gardens Bleaching handout (attached; one per student)

  • Claim Evidence Reasoning (CER) handout (attached; one per student)

  • Student devices with internet access

  • Notebook paper

  • Pen/pencil


Use the attached Lesson Slides to guide the lesson. Begin the class by displaying slide 3. Show students the embedded BBC Earth’s coral reef video. Don’t be intimidated by the 10-hour video loop! Show only the first 3–5 minutes to give students an idea of what a healthy reef looks like.

Next, move to slide 4 and display images of bleached coral.

After viewing the video and images, have a few students share what they think may have caused the coral to look bleached. Move to slide 5 and show the embedded “Coral Reefs 101” video from National Geographic. The video explains how coral bleaching occurs (i.e., stressed coral "evict" their symbiotic algae).

Before continuing the lesson, facilitate a brief discussion to help students orient their thinking to why having algae would help feed corals.

Move through slides 6–7 to review the essential question and lesson objective with students.


Move to slide 8 and have students navigate to the Concord Consortium Leaf Photosynthesis Activity homepage. Guide students as they complete the activity.

The activity includes three simulations that illustrate the inputs and outputs of photosynthesis as they are processed in the chloroplasts of a leaf. Students can adjust sun brightness, amount of CO2, and water flow and observe how each adjustment changes the process. The analysis questions at the end of the activity focus on photosynthesis inputs and outputs and how people depend upon photosynthesis. There are also a few brief career-related questions at the end of the analysis that you may find valuable.

During the Leaf Photosynthesis Activity, circulate the room and provide feedback as students work. Consider using the answers in the activities as an additional formative assessment.


Have students take notes as you review the results of the simulation with students. This will be most effective if students draw a model or diagram that illustrates photosynthesis inputs and outputs as the class discusses the simulation. Be sure to illustrate this on the board or somewhere else visible to students.

Using the I Think / We Think strategy, develop a list of environmental conditions that might (1) stress coral enough to evict their algae, and (2) affect photosynthesis, either negatively or positively. Have students draw a t-chart on a piece of notebook paper and label the columns with “I Think” and “We Think”.

Display slide 9 and have students record their own ideas in the "I Think" column. After students record their thoughts, ask for some volunteers to share their ideas. As the volunteers share their ideas, have the other students fill in the “We Think” column with ideas they didn’t think of themselves. To scaffold this, consider having students think through each question individually rather than all at the same time.


Among other threats to coral, students will focus on a few that have direct impacts on both photosynthesis and coral survival (such as changes in light, heat stress, and oxygen depletion).

Move to slide 10 and pass the attached Coral Bleaching Graphic Organizer to each student. Using the Chat Stations strategy, number students into groups of two to four. Point out the posted chat stations around the room and tell students to visit each station as a group. At each station, they should discuss the material provided on the cards to determine the most important idea(s) for how the conditions lead to coral bleaching or affect photosynthesis. They should record this information in their graphic organizer.


Have students return to their seats. Pass out the attached Flower Gardens Bleaching handout and the attached CER handout to each student. Display slide 11 and provide time for students to read the Flower Gardens Bleaching handout. Then, have students use the Claim, Evidence, and Reasoning (CER) strategy by writing a claim, evidence, and reasoning to the question on the slide: “What caused the bleaching of Flower Gardens Banks National Marine Sanctuary?” In their response, students should include evidence from the photosynthesis activity, class notes, and/or chat station notes. The CER handout guides students as they write their claim, evidence, and reasoning items.

Display slide 12 and conclude the lesson by having students reflect on what they have learned using the 3-2-1 strategy. Ask students to write their reflections on the back of their CER handouts. Collect students' CER handouts and review both their CER and 3-2-1 responses to assess student understanding of the lesson content.