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Interactive Exploration of Coral Bleaching
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OVERVIEW
Interactive Exploration of Coral Bleaching is an animation with automatic pause points, during which students
access additional information in the form of text, illustrations, videos, questions, and interactive widgets. This
information allows for a richer exploration of coral reefs, symbiosis, and other topics in biology.
The animation zooms in to explore the tiny animals that build reefs, the photosynthetic algae inside their cells,
and the damaging process of coral bleaching. The examples in this animation can be used to explore the
concepts of biodiversity and ecosystem services, sexual and asexual reproduction, the differences between plant
and animal cells, symbiotic relationships, photosynthesis, and more.
This document contains multiple resources for using the interactive exploration with students, including the
following (select links to go directly to each section):
• general teaching tips for this resource, including common misconceptions and scientific language support
• suggested procedures for providing context, using the interactive exploration, and using the “Student
Worksheet”; includes a table of the main topics covered and where to find them
• assessment guidance for the “Student Worksheet”
Additional information related to pedagogy and implementation can be found on this resource’s webpage,
including suggested audience, estimated time, and curriculum connections.
KEY CONCEPTS
• Coral reefs support high biodiversity and provide a variety of ecosystem services.
• Coral reefs are colonies of animals called polyps, which rely on symbiotic algae for survival.
• Coral bleaching reduces coral survival by driving polyps to destroy or expel their symbionts.
• Most coral bleaching worldwide is caused by unusually warm temperatures due to climate change.
STUDENT LEARNING TARGETS
For the “Student Worksheet”:
• Part 1: Coral Reefs
o Identify living and nonliving components of an ecosystem and their potential interactions.
o Describe how ecosystems, such as coral reefs, benefit humans and other organisms.
• Part 2: The Corals
o Differentiate between sexual and asexual reproduction.
o Compare plant and animal cells, including their major structures and how they use energy.
• Part 3: The Symbiont
o Identify different types of symbiotic relationships, based on descriptions of how organisms interact.
o Describe the process of endocytosis.
• Part 4: The Chloroplasts
o Diagram the process of photosynthesis.
o Distinguish between photosynthesis, cellular respiration, and their corresponding organelles.
o Interpret and explain the value of simple models.
• Part 5: Coral Bleaching
o Explain the process of coral bleaching and how it can be caused by climate change.
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o Describe the impacts of coral bleaching on corals and other organisms.
o Describe the process of exocytosis and how it compares with that of endocytosis.
PRIOR KNOWLEDGE
Students should have a basic understanding of:
• characteristics of living vs. nonliving things
• biological organization (cells to ecosystems)
• cell structure and organelles
• climate change
TEACHING TIPS
General
• This resource covers a broad range of topics, so you should tailor which parts you use to your course
learning objectives and students’ needs. The “Using the Interactive Exploration”
section below provides
more information on the different modules and their contents.
• Students are encouraged to watch the entire animation without pause points first. You can access a version
of the animation without pause points from the Coral Bleaching webpage.
Common Misconceptions
Student misconceptions and points of confusion may include the following:
• Students may have the misconception that corals are not animals. They may think that corals are rocks due
to the hard structures of reefs, or that coral polyps are plants due to their flower-like bodies.
o The interactive exploration addresses this in “The Corals” module.
o The “Student Worksheet” addresses this in Question 9.
• Students may have the misconception that coral cells contain chloroplasts and can perform photosynthesis
on their own. However, chloroplasts are not part of the coral cells but rather are part of the zooxanthellae
(symbiotic algae) that live inside coral cells.
o The interactive exploration addresses this in the modules “The Corals” and “The Chloroplast.”
o The “Student Worksheet” addresses this in Question 14.
• Students may have the misconception that plants and zooxanthellae only perform photosynthesis and not
also cellular respiration. Plants and zooxanthellae have both chloroplasts for photosynthesis and
mitochondria for cellular respiration. So, they can produce food (sugars) through photosynthesis and break
down that food for energy through cellular respiration.
o The interactive exploration shows that plants have both mitochondria and chloroplasts in the “Corals
Are Animals” section of the module “The Corals.”
o The “Student Worksheet” addresses this in Question 14.
Scientific Language Support
The scientific language in the resource may be new and overwhelming to students. Provide support as needed,
which could include the following strategies:
• Clarify what students should focus on early.
o At the start of a lesson or activity, share the learning objectives with students. Ask students to focus on
addressing these objectives, rather than on memorizing scientific terms.
o Provide students with a short list of specific terms they will be expected to know and use in class (if any).
• Help students access information about the terms.
o Make students know that they can select bold underlined terms throughout the interactive exploration
to view their definitions.
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o The “Glossary” in the “Materials” section of this resource’s webpage contains a list of the scientific
terms in the resource. You may wish to adapt and share it with your students.
• Implement strategies for helping students learn key terms.
o Guide students through learning and using key scientific terms using the activity “Learning Scientific
Language with a Graphic Organizer.” The “Educator Materials” document for that activity provides
additional suggestions for supporting language learning.
o Encourage students to continually practice explaining their ideas about science and scientific terms.
Repeated practice can help students build stronger language skills.
PROCEDURE
Usage of the interactive exploration and its materials is flexible and can be adapted based on your classroom
context. As a starting point, some suggestions are provided for the following (select links to go directly to each
section):
• Providing Context
• Using the Interactive Exploration
• Using the Worksheet
Providing Context
Before starting the activity, it is recommended to provide students with a clear transparency statement about
the purpose of the activity and what they will get out of doing it.
• The “Introduction” section of the “Student Worksheet” provides an example; modify this text as needed to
add context and relevancy for your students.
• Not all students may be familiar with or particularly interested in coral reefs. You may need other ways to
relate the content to students’ contexts. For example, you could:
o Highlight how the concepts apply more broadly to other organisms or ecosystems.
o Discuss the impacts of climate change on more local contexts.
o Make connections to environmental justice and human inequities (e.g., Donner and Potere 2007
).
o Have students come up with their own applications, as in Questions 4 and 11 of the "Student
Worksheet."
You may also want to provide context for the locations mentioned in the interactive exploration by showing
students where they are on a map.
• The first module, “Coral Reefs,” has a map of coral reef locations worldwide that you can reference.
• You could point out the location of Ofu in American Samoa, which is referenced at the beginning of the
animation, and of the Great Barrier Reef in Australia, which is referenced in the fifth module, “Coral
Bleaching.”
Using the Interactive Exploration
The interactive exploration uses coral reefs to illustrate how multiple key biology concepts are connected. It
contains five automatic pause points, during which students access modules with additional information in the
form of text, illustrations, videos, and questions. Descriptions of each module are as follows:
1. Coral Reefs introduces the coral reef ecosystem and how it benefits humans and other organisms. It
explores the concepts of ecosystems, biodiversity, and ecosystem services.
2. The Corals examines the characteristics of coral polyps, the tiny organisms that make up coral reefs. It
introduces the differences between sexual and asexual reproduction, and plant and animal cells.
3. The Symbiont focuses on zooxanthellae, the symbiotic algae that live inside coral tissue. It includes the
concepts of symbiosis (mutualism, parasitism, and commensalism), autotrophy, and endocytosis.
4. The Chloroplasts shows how zooxanthellae use chloroplasts to produce food. It introduces photosynthesis
and some of the cellular structures involved in this process.
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5. Coral Bleaching explains why corals may lose their zooxanthellae and how this affects both corals and the
ecosystems they support. It describes the mechanisms for coral bleaching, including the role of rising
temperatures, and its consequences for coral reefs worldwide.
Depending on your class, you could use all the modules or choose to assign only certain parts.
• For a general biology course, the resource as a whole could be used for an end-of-the-year review.
Determine which sections students should focus on based on the content of your course.
• For more specific lessons, use Table 1 to determine which modules and module sections would be the most
relevant. Related questions from the “Student Worksheet” are also provided.
Table 1. A summary of the main topics covered in this resource, including the relevant modules in the
interactive exploration and related questions from the “Student Worksheet.”
Area Topics Module Sections in the Module
Worksheet
Questions
Ecology Ecosystems
Coral Reefs Coral Reef Ecosystems 1, 2, 4
Biodiversity
Coral Reefs Biodiversity of Coral Reefs 1
Autotrophs and
heterotrophs
The Corals Corals Are Animals 7, 9, 14
The Symbiont Symbiosis with Corals
Symbiotic relationships
The Symbiont What Is a Symbiont 10, 11, 12
Environmental
science
Ecosystem services
Coral Reefs Ecosystem Services of Coral
Reefs
1, 3, 4, 20
Human impacts on
ecosystems
Coral Bleaching What Is Coral Bleaching,
Global Consequences of
Bleaching
17, 18, 20
Climate change
Coral Bleaching How Temperature Triggers
Bleaching
18
Cell biology Plant vs. animal cell
structure and organelles
The Corals Corals Are Animals 6, 9
Asexual vs. sexual
reproduction
The Corals Why Are Polyps in a Colony
Identical
5
Endocytosis
The Symbiont How Corals Get Symbionts 13, 19
Exocytosis
Coral Bleaching How Corals Get Rid of
Symbionts
19
Cellular respiration
The Corals Corals Are Animals 14
Photosynthesis
The Chloroplast What Are Chloroplasts 14, 15
Chloroplast function and
structure
The Chloroplast What Are Chloroplasts,
Structure of a Chloroplast
14, 16
Science
practices
Using geographical maps
Coral Reefs Coral Reef Ecosystems
Using heat maps
Coral Bleaching How Temperature Triggers
Bleaching
Using cell and anatomical
diagrams
The Corals Corals Are Animals, The
Parts of a Polyp
6, 8
Using 3D models
The Chloroplast What Are Chloroplasts,
Structure of a Chloroplast
16
Using the Worksheet
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The “Student Worksheet” is designed to guide students through the entire interactive exploration. It is divided
into parts that correspond to different modules of the interactive exploration. The “Worksheet Questions”
column of Table 1 above lists which questions correspond to which topics.
General recommendations for using this worksheet are as follows:
• Customize the worksheet as needed to better fit your learning objectives and students’ needs. For example,
you may want to assign only certain parts, modify or remove questions, or add more explanations.
• Have students work in pairs or small groups. Students may benefit from discussing their ideas with each
other.
• Address student questions. The “Before and After the Exploration” section at the beginning of the
worksheet has students pose their own questions. If possible, acknowledge and answer these questions
during a small-group or whole-class discussion.
The worksheet includes several intentionally open-ended questions to increase student choice and relevancy.
For example:
• Questions 4 and 11 ask students to apply the concepts to new examples of their choice.
• Questions 12, 15, and 19 ask students to create their own diagrams or explanations to connect multiple
terms.
Consider having students share their responses to these open-ended questions in small groups or as a class. This
can help center students’ voices and show a greater diversity of perspectives. You could also provide options for
students to respond in different formats (e.g., presentation, poster, audio recording, etc.).
ASSESSMENT GUIDANCE
Before and After the Exploration
The purpose of this section is to engage students and have them reflect on their own learning. Student answers
will vary; be open to a range of reasonable responses.
PART 1: Coral Reefs
1. Define each of these terms in your own words.
Student answers will vary. Definitions from the resource are shown below.
a. Ecosystem
A community of organisms interacting with the environment in a particular area.
b. Biodiversity
The variety of species in an ecosystem.
c. Ecosystem services
The various ways in which humans benefit from ecosystems.
2. All ecosystems, including coral reefs, have both living and nonliving components that interact.
a. Describe three specific living components of a coral reef. (Hint: These could be examples of organisms
found in coral reefs.)
Student answers will vary. Examples include corals and any of the other animals discussed in the
“Biodiversity of Coral Reefs” section, such as crustaceans, fish, sea urchins, turtles, etc.
b. Describe three specific nonliving components of a coral reef. (Hint: These could be characteristics of the
environments where coral reefs are typically found.)
Student answers will vary. Examples include lots of sunlight, warm temperatures, shallow depth (by
the coast), salt water (in the ocean), etc.
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c. Pick one living component and one nonliving component. Give an example of how they could interact.
Student answers will vary depending on the parts they chose; be open to a range of reasonable
responses.
3. Imagine that you are writing for an environmental group’s social media account. Write 3–4 sentences to
persuade the general public that coral reefs are valuable. Include at least two specific ecosystem services.
Student answers will vary depending on the ecosystem services they chose. Examples include benefits to
fisheries, tourism, shoreline protection, medicine, nutrient cycling, and culture.
4. Think of an ecosystem that is not a coral reef. This ecosystem could be one that you’ve learned about, or
one that you are personally interested in or familiar with. You could pick an ecosystem that covers a smaller
area, such as a pond or a garden, or one that covers a larger area, such as an entire city or region.
a. Describe three specific living components of this ecosystem.
b. Describe three specific nonliving components of this ecosystem.
c. Describe two specific ecosystem services that this ecosystem could provide.
These questions parallel the previous questions and have students transfer these concepts to a new
ecosystem of their choice. Student answers will vary depending on the ecosystem they chose. Consider
having students share their responses in small groups or as a class.
PART 2: The Corals
5. One characteristic of living things is that they can reproduce.
a. Explain the difference between asexual reproduction and sexual reproduction.
Asexual reproduction has only one parent and produces offspring that are genetically identical to that
parent. Sexual reproduction has two parents and produces offspring that have combinations of the
parents’ DNA.
b. Does asexual reproduction or sexual reproduction lead to greater genetic diversity? Why?
Sexual reproduction leads to greater genetic diversity, because it produces organisms with new
combinations of genetic material.
6. Another characteristic of living things is that they are made of cells. The table below describes some
common cell parts and whether they are found in coral cells. Use the diagram in the interactive exploration
to complete this table.
Part
Function
In coral cells? (Yes/No)
Nucleus
Contains the cell’s DNA and controls cell growth.
Yes
Cell wall
Provides protection and support for the cell.
No
Mitochondria
Performs cellular respiration to produce energy that
can be used by the cell.
Yes
Chloroplast
Performs photosynthesis to convert energy from the
sun into chemical energy stored in organic molecules.
(Students will learn more about photosynthesis in the
fourth module, “The Chloroplast.”)
No
7. Autotrophs and heterotrophs are two main groups of living things.
a. Explain the difference between an autotroph and a heterotroph.
An autotroph produces its own food. A heterotroph relies on other organisms for food.
b. Are corals autotrophs or heterotrophs? Provide evidence for your decision.
Corals are heterotrophs because they rely on other organisms for food. For example, corals catch and
eat zooplankton. (Students will learn that corals also get food from zooxanthellae in the third module,
“The Symbiont.”)
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8. The table below describes the parts of a coral polyp. Use the diagram in the interactive exploration to
complete this table.
Function
Contains stinging cells in the tentacles to help catch prey.
Provides protection and support for the polyp.
Produces egg and sperm for sexual reproduction.
Contains organisms called zooxanthellae. (Students will learn more about
the role of zooxanthellae in the third module, “The Symbiont.”)
Digests food.
Takes in food and releases waste.
9. Imagine that a classmate tells you corals are either a type of rock or a plant. How could you explain to them,
with at least two pieces of supporting evidence, why that claim is incorrect?
Student answers will vary. An example response:
Corals are living things because they can reproduce and are made of cells. This means that corals can’t be
rocks, though they do create hard, rock-like structures. Corals are also heterotrophs, meaning that they
get food from other organisms. For example, they catch prey using their tentacles. Plants are typically
autotrophs, not heterotrophs, and don’t have tentacles, so corals are not plants either. Corals are actually
a type of animal called a cnidarian.
PART 3: The Symbiont
10. Assign each symbiosis in the table below to a specific type (mutualism, parasitism, or commensalism) based
on its description.
Description of the symbiosis
Type of symbiosis
Bacteria in a human’s intestines feed on large sugar molecules. The bacteria
break these sugars down into smaller molecules that human cells can use.
Mutualism
A tapeworm in a pig’s intestines feeds on partially digested food, taking
nutrients away from the pig.
Parasitism
An ant colony lives inside a tree. The ants kill other plants nearby that could
compete with the tree for resources.
Mutualism
A bird builds a nest on a tree, without affecting the tree’s growth or survival.
Commensalism
11. Think of another relationship that could be a symbiosis, which is not from the table above or the interactive
exploration. The example can be from something else you learned or your own interests/experiences.
a. Briefly describe the relationship you chose.
b. Explain why you think this relationship is a symbiosis.
c. What type of symbiosis do you think this relationship is, and why?
These questions have students transfer their knowledge of symbiosis to a new example. Student answers
will vary depending on the example they chose. Consider having students share their responses in small
groups or as a class.
12. Create a diagram, such as a concept map, that shows how the following terms are connected.
• Algae
• Coral polyps
• Coral reefs
• Gastrodermis
• Mutualism
• Photosynthesis
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• Symbiosis
• Zooxanthellae
Student
diagrams will vary. An example is shown below.
To scaffold this question, you could give students a version of the concept map with blank boxes, as shown
below. Students could then fill in the missing boxes instead of creating their own concept map from scratch. If
desired, you could fill in some of the boxes as examples or have students use an online whiteboard, such as
Google Jamboard.
13. Thin
k about the cellular process that brings zooxanthellae from the water into coral cells.
a. What is this process called?
Endocytosis (or, more specifically, phagocytosis)
b. In one or two sentences, summarize how this process works.
The cell membrane pinches inward to surround the zooxanthellae. The membrane forms a sac-like
structure called a vesicle, which carries the zooxanthellae into the cell.
PART 4: The Chloroplast
14. Determine whether corals and zooxanthellae have each characteristic in the table below. Complete the
table by writing either “Yes” or “No” in the corresponding columns. (For some of this information, you may
want to review the “Corals Are Animals” section at the second pause point, “The Corals.”)
Coral polyps
Zooxanthellae
Gastrodermis
of
live in the
Mutualism
Symbiosis
is a type of
is the
relationship
between
Coral reefs
which build
Algae
Photosynthesis
which make
food using
are a
type of
helps provide
food for
of
live in the
is a type of
is the
relationship
between
which build
which make
food using
are a
type of
helps provide
food for
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Characteristic Corals Zooxanthellae
Has chloroplasts. No Yes
Can perform photosynthesis. No Yes
Uses food (sugars) that was produced by photosynthesis. Yes Yes
Has mitochondria. Yes Yes
Can perform cellular respiration. Yes Yes
If students struggle with this question, you may need to remind them that heterotrophs like corals have
mitochondria but not chloroplasts. Autotrophs like zooxanthellae have both mitochondria and
chloroplasts. Chloroplasts perform photosynthesis, which produces food (sugars). Mitochondria perform
cellular respiration, which breaks down food (sugars).
15. Create a diagram, such as a concept map, that shows how the following terms are connected. The style of
this diagram can be similar to the one in Question 12.
• Carbohydrates
• Carbon dioxide
• Chemical energy
• Light energy
• Oxygen
• Photosynthesis
• Water
Student diagrams will vary. An example is shown below.
To scaffold this question, you could give students a version of the concept map with blank boxes, as shown
below. Students could then fill in the missing boxes instead of creating their own concept map from
scratch. If desired, you could fill in some of the boxes as examples or have students use an online
whiteboard, such as Google Jamboard.
is converted by
into
Light energy Photosynthesis
powers
Chemical energy
Carbon dioxide Water
Carbohydrates Oxygen
uses
up
produces
store
is converted by
into
powers
uses
up
produces
store
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16. The image below shows part of a 3D model that appears in the video.
a. Label and/or describe how chloroplasts, thylakoids, pigments, and photosystems are represented in
this model.
Student answers will vary. An example with labels is shown below.
To scaffold this question, you could give students a version of this image that has the parts labeled
with numbers, as shown below. Students could then match the terms to the numbers.
b. What might be an advantage of using a model in the video rather than showing real images of the
organism?
Student answers will vary. They could say that the model helps us visualize features that are too small
to see directly and simplifies things so that we can focus on the specific parts involved in
photosynthesis.
PART 5: C
oral Bleaching
17. Coral bleaching is a major threat to coral reefs worldwide.
a. Why is coral bleaching dangerous for corals?
Coral bleaching is a process where corals force zooxanthellae out of their cells. This is dangerous for
corals because they rely on zooxanthellae for most of their food. If the corals are without
zooxanthellae for too long, they can die.
b. Why does coral bleaching cause corals to lose their color?
Most of a coral’s color comes from zooxanthellae. During bleaching, the coral loses its zooxanthellae,
so it also loses its color.
18. Write a paragraph or create a diagram that explains how climate change can cause coral bleaching. Include
the following terms:
• climate change
The entire rounded
structure is part of
a chloroplast.
The thin layers inside
the chloroplast are
the thylakoids.
The dots on the
thylakoids are
photosystems. The
pigments are part of
the photosystems.
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• coral bleaching
• coral polyps
• heat stress
• photosystems
• reactive oxygen molecules
• zooxanthellae
Student answers will vary. An example response:
Clim
ate change is causing ocean temperatures to warm, which increases stressful heat conditions called
heat stress. The heat stress can damage the photosystems in zooxanthellae, causing them to produce
harmful reactive oxygen molecules. To protect themselves from these harmful molecules, coral polyps
force the zooxanthellae out of their cells, which results in coral bleaching.
19. Compare the processes of exocytosis and endocytosis (discussed at the third pause point, “The Symbiont”).
How are these processes similar, and how are they different?
Bo
th exocytosis and endocytosis are cellular processes that transport materials across the cell membranes
using vesicles. These processes differ in terms of direction: endocytosis transports materials into the cell,
whereas exocytosis transports materials out of the cell.
20. Co
ral bleaching negatively impacts not only corals but also many other organisms.
a. Propose two specific negative impacts that coral bleaching may have on humans.
Student answers will vary and may include reduced availability of seafood, economic losses for
fisheries and tourism, increased storm damage in coastal areas, loss of important cultural sites, etc. If
students struggle with this question, you may want them to review the ecosystem services in the first
module, “Coral Reefs.”
b. Propose two specific ways that humans could help reduce coral bleaching.
Student answers will vary. One strategy mentioned in the resource is transplanting heat-resistant
corals to damaged reefs. Students may suggest other ways to restore or cool down coral reefs. They
may also suggest ways to mitigate climate change, as it is the main cause of coral bleaching.
CREDITS
Written by Esther Shyu, HHMI; Sue Dodge
Based on a draft by Melissa Haswell, Davenport University, MI
Edited by Laura Bonetta, HHMI