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ESTABLISHING A BASELINE ACTIVITY 1

FIGURE 1.10: Wild rice

a. Obtain Student Sheet 1.1, “Population Estimation Methods,” which
shows a grid that represents a study area at the edge of a lake where
wild rice grows. The study area is divided into 6 rows and 6
columns, totaling 36 sections, called quadrats.

b. You have enough time to count the wild rice plants in 6 randomly
chosen quadrats. Use the number cubes to determine which
quadrats to examine. The white cube will tell you which row your
quadrat is in, and the blue cube will tell you which column your
quadrat is in. For example, if you roll a white 3 and a blue 2, you
will sample the quadrat in row 3, column 2. Once you have selected
a quadrat, circle it on your Student Sheet. If you roll a combination
more than once, roll again. Continue this process until you have
selected 6 random quadrats.

c. Collect the data from the Wild Rice Quadrats as instructed by your
teacher. Record the data on Student Sheet 1.1. Do this for the 6
quadrats you are sampling.

d. Based on these 6 quadrats, estimate how many wild rice plants are
in the entire study area of 36 quadrats.

Mark-and-Recapture Sampling Method

Grasshoppers are an important part of many ecosystems, but some
grasshopper species also can cause significant damage to crop plants.
Imagine that you are an agricultural scientist monitoring a grasshopper
population. Because the grasshoppers jump around a lot, you can’t count
all the grasshoppers you see because you may count the same grasshopper
several times. Instead, you will use the mark-and-recapture sampling
method to estimate the size of the grasshopper population.

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ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

FIGURE 1.11: This Monarch butterfly
has been tagged so ecologists can
monitor it to collect data over time.

a. Obtain Student Sheet 1.1, “Population Estimation Methods,” a bag
of disks, a timer, and some masking tape. The bag represents the
field, and each disk in the bag represents a grasshopper in the field.

b. Have one person “catch” grasshoppers, one at a time, while the
other person times them for 30 seconds. Record the number of
grasshoppers you caught on Day 1 on the Student Sheet.

c. Mark each grasshopper with masking tape and return it to the field
by returning the marked disks to the bag.

d. Shake the bag for 30 seconds to simulate the passage of time. This
allows the marked grasshoppers to mix back with the rest of the
population.

e. On Day 2, switch roles: Have one person “catch” grasshoppers, one
at a time, while the other person times them for 30 seconds. Count
and record both the total number of grasshoppers and the number
of marked grasshoppers you caught on Day 2.

f. Use the proportion of marked grasshoppers you caught on Day 2 to
estimate the total size of the grasshopper population.

3. When both pairs in your group have finished estimating their
populations, explain your methods to each other. Be prepared to share
your estimates for the wild rice and grasshopper populations with the
rest of the class.

4. Follow your teacher’s instructions to have a class discussion about the
results of your investigations and how scientists might use data like the
data your group gathered.

5. Work with your group to answer Build Understanding item 1.

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ESTABLISHING A BASELINE ACTIVITY 1

Build Understanding

1. Estimate population size in the following two scenarios, using either the
quadrat sampling method or the mark-and-recapture sampling method:

a. S cientists have been monitoring the 4
recovery of a field of alfalfa after it 23
was severely damaged by
grasshoppers. Figure 1.12 is a 40
drawing of the scientists’ grid,
representing the entire field. Each 12
cell is a quadrat. The shaded cells 3
represent the quadrats sampled, with
the number of plants counted in
each. Estimate the size of the alfalfa
plant population in the entire field.

b. Researchers want to determine how 2
many fish are in a lake. They use
nets designed to catch the fish 5
without harming them. The
researchers mark the fish with a FIGURE 1.12: Alfalfa data
small tag, then release them back into the lake. After a period of
time, the researchers set, and later check, the nets again. Use
their data below to estimate the total fish population in the lake:

Number of fish caught on Day 1: 32

Number of marked fish caught on Day 2: 7

Total number of fish caught on Day 2: 28

2. What do both methods for estimating population size (quadrat FIGURE 1.13: These fish
sampling and mark-and-recapture sampling) have in common? have been tagged so that

3. Which method would work better for measurELiaCnbOgA3eiedasScBSh/ETPoEUf0Pt1hS_eG1f2IoEucorlogy 3ethey can be identified and
populations described in the introduction? WMhyyri?ad Pro Semibold data can be collected about
them over time.

4. Why is it important to estimate
population size? What kinds of
information do we get from
population size, and what could that
information be used for?

5. Issue connection: Why do you think
measuring or estimating population
size is important for fisheries? How
might this data be used to determine
the sustainability of a fishery?

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ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

KEY SCIENTIFIC TERMS

fishery
population

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2 Population Growth Models

i n t h e l a s t ac t i v i t y , yo u observed that populations of organismsPopulation size

may show dramatic changes—either increases or decreases—over time.
What factors cause populations of organisms to change over time? Why do
different populations have different growth patterns? When and where
might you expect to see these different patterns? In this activity, you will
explore mathematical models of population growth to see what types of
population changes can cause these patterns. You will then consider how
this information can be used in fisheries management.

2
3
4

1

Time

FIGURE 2.1: Four populations over time

GuidiLnabgAidQs SuEPeUsPtSiGoI Encology 3e

What cFMaigynuriraped:aPEtrcotoeR3reengSsB9i.05n2/1_d11ata tell us about the status of a
population of organisms?

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ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

Materials

FOR EACH PAIR OF STUDENTS

bag of ~150 hexagonal plastic discs
cup
set of colored pencils
computer with Internet access

FOR EACH STUDENT

Student Sheet 2.1, “Predicting Population Growth”

Procedure

Part A: Population Growth Model

There are many ways to model population growth. The first method you
will work with is a simple hands-on model using plastic discs. The
following rules apply to this model:

• Each disc represents an individual organism in one population of discs.
• Discs reproduce by cloning (making an exact copy of themselves).
• Discs reproduce randomly. Discs are black on one side and white on the

other. Only discs that land with the black side facing up reproduce.

1. Make a chart in your science notebook like the one shown below,
leaving enough room for up to 15 rows.

TIME POPULATION SIZE (NX)
0 2
1
2
3
4
5

2. Place 2 discs in a cup. This is the population size, N, at time 0, so it is
designated as N0.

3. Shake the cup and pour out the discs.
4. Count the number of discs with the black side facing upward; these

discs reproduce. For every disc showing the black side, add another
disc to the population.
5. Record the new total population size for the next time period.

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POPULATION GROWTH MODELS ACTIVITY 2

6. Place all the discs from the population in the cup and repeat Steps 3–5
until either you complete 15 time periods or you run out of discs.

7. Graph the data from your data table, with time on the x-axis and
population size on the y-axis.

8. Examine your graph with your partner. Describe the pattern of
population growth, and discuss whether it resembles any of the lines in
the graph in the introduction.

9. Imagine a different species of discs that produces 2 offspring at a time
instead of 1. What would happen to the growth rate for this second
population? Add your prediction to your graph. Be sure to label the
prediction line.

10. Imagine a third species of discs where 10% of the population dies after
they reproduce. What would happen to the growth rate for this third
population? Add this prediction to your graph. Be sure to label the
new prediction line.

Part B: Defining r

In Steps 9 and 10, you made predictions based on different growth rates for
the disc populations. Different species (or populations of species) have
different potential for population growth—some higher and some lower,
depending on how quickly they reproduce and die. A species’ rate of
population growth is referred to by ecologists as its intrinsic growth rate,
or r. Values of r vary greatly for different species. A lower r means a lower
potential for population growth, and a higher r means a higher potential.
11. Discuss with your partner whether you were increasing or decreasing r

in Steps 9 and 10.
12. Discuss with your partner which kinds of species you predict have

higher r values and which have lower r values. Be sure to explain your
reasoning. For example, would you predict elephants have a high or a
low r? Why? What about fleas?
13. Examine the table of r values that your teacher shows you. Do your
predictions in Step 12 generally correspond to the data in this table?

Part C: Exponential Population Growth

In the disc model in Part A, you modeled a population that grew without
any limitations. That population increased very quickly. This type of growth
is called exponential growth. To investigate exponential population growth
in large populations over long periods of time, you will use a computer
simulation to explore different scenarios.

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ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

14. Follow your teacher’s instructions for accessing the first simulation.
15. With your partner, examine how changing the starting population size,

N0, affects the population growth over time. Look for patterns in how
the data changes as you change only the N0 value. Record your
observations in your science notebook.
16. With your partner, examine how changing the r value affects the
outcome, and record any patterns you see in your science notebook.
Be sure to test r values below and above 1.0.
17. Examine Table 2.1. With your partner, discuss what patterns you think
you will see in the simulation when you test the data for each species
in the table. On Student Sheet 2.1, “Predicting Population Growth,”
use a colored pencil to sketch a line to show your prediction for each
species’ population growth. Label these lines “Prediction.”

TABLE 2.1: Population Growth Variables for Four Species

SPECIES N0 r T
Orca
24 0.02 100

Elephant 300  0.025 100

Sockeye salmon 150 0.23 15

Water flea 10 69 20

18. Run the simulation for each of the four species in Table 2.1, using the
data provided. For each species, on Student Sheet 2.1 add a line in a
different color of what the actual data looks like. Label these lines
“Observed.”

19. Briefly discuss each graph with your partner. Does the population
growth that the simulation calculated seem realistic? Why or why not?
What is happening to the rate of growth over time? Summarize your
reasoning in the space provided on Student Sheet 2.1.

20. With your partner, read the text about Ngorongoro Crater in Tanzania.
Compare this information to what you predicted and modeled for the
elephants in Steps 17–19. Does the data from the model seem realistic
for the elephants that live in Ngorongoro Crater? Why or why not?
Discuss your ideas with your partner.

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POPULATION GROWTH MODELS ACTIVITY 2

Ngorongoro Crater, Tanzania FIGURE 2.2: Ngorongoro Crater in Tanzania
This unique area is found in a volcanic caldera,
The Ngorongoro Conservation Area in a large, steep-sided crater. Approximately
Tanzania is home to a variety of African 25,000 large animals live in the crater. It is about
animals, including zebra, rhinoceros, lions, 610 meters deep, and the floor is approximately
hyenas, wildebeest, and Savannah elephants.
260 square kilometers. Most of the
FIGURE 2.3: Elephants living in Ngorongoro Crater animals stay within this “natural
enclosure” for much of their lives,
although some do migrate in and
out. The Savannah elephant
population in Ngorongoro Crater
seems to stay fairly stable, at
around 300 elephants, and this
population has been studied
extensively. There are more males
than females. The elephants live in
small groups, and there is
evidence that some elephants
occasionally enter and leave the
crater. There are often slightly
more elephants in the crater
during the rainy season.

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ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

Part D: Limits to Population Growth

The exponential growth model has no limits on population growth—but in
reality there are often many limits, such as the limited availability of food or
other resources. In the next model, limits to the population size have been
added; the population cannot go above a certain number. This is called the
population’s carrying capacity—the maximum number of individuals that
can exist in a particular environment. In the simulation, the model that
includes carrying capacity is called the logistic growth model.
21. Follow your teacher’s instructions for accessing the second simulation.
22. Similar to the exponential growth model, this model allows you to

change the starting population size, N0, and the intrinsic rate of
population growth, r. It also allows you to change the carrying
capacity, K. Examine how adding carrying capacity to the model
affects the population growth rate.
23. Follow your teacher’s instructions for a class discussion about carrying
capacity and how it affects population growth rates.

Build Understanding

1. What features do both the exponential growth model and the logistic
growth model have in common? How do they differ?

2. Under what conditions would a population of organisms grow
exponentially?

3. Both the exponential and logistic growth models are used to describe
populations that are increasing in size.
a. Describe three factors that might cause a population to decrease in
size (meaning, show negative population growth).
b. For each factor, sketch a graph that shows the pattern of population
decrease you expect to see.

4. Use what you have learned in this activity to hypothesize what might
be happening to the four populations shown in the graphs in Activity
1: Establishing a Baseline.
a. yellow perch
b. purple sea urchins
c. trees
d. song sparrows

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POPULATION GROWTH MODELS ACTIVITY 2

5. Fisheries management often involves studying population data.
a. What kinds of data would help determine if a fishery is sustainable?
b. How could understanding the growth rate of a fish species be
helpful in fisheries management?

6. Issue connection: Scientists have determined that the most productive
fishery is one that is at half the carrying capacity for the population
being fished. What might explain this?

Hint: Look at the logistic growth model curve.

KEY SCIENTIFIC TERMS

carrying capacity (K)
exponential growth
intrinsic growth rate (r)

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3 Factors Affecting Population Size

i n t h e p o p u l at i o n g r a p h s yo u analyzed in the last two activities,
you saw that populations of organisms can show a variety of patterns over
time. Sometimes populations remain stable, and at other times population
size may increase or decrease. This change can be gradual or rapid. You
have started identifying some factors that may cause a population to
change in size or that limit it to a certain size. In this activity, you will
investigate several specific factors that affect the population size of the
Mandarte Island song sparrow population that you read about in Activity
1. You will consider how scientists can use what they learn from studying
this bird population to better understand and help manage other
populations of organisms, such as fish.

Guiding Question

What factors affect population size in song sparrows?

FIGURE 3.1: Ecologists use small leg bands to identify
and keep track of individual song sparrows over time.

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ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

Materials

FOR EACH PAIR OF STUDENTS

Student Sheet 3.1, “Predictions of Nesting Success in Song Sparrows on
Mandarte Island”
computer with Internet access

Procedure

1. With your partner, brainstorm a list of factors that you think might
influence population size for the song sparrows on Mandarte Island.
Try to think of at least five factors. Record your ideas in your science
notebook.

2. Complete the following reading about the song sparrow study.

Song Sparrows on Mandarte Island

The song sparrow population on Mandarte Island has been carefully
studied by scientists since 1975. The population is relatively isolated from
the mainland, so there is little migration of birds into or out of the
population. Every bird is individually marked with leg bands and has had
blood samples collected by scientists. Using population data collected over
time, researchers have been able to map the “family tree” for all birds on
the island. Because this is a small, isolated population, nearly all the birds
are genetically related to some extent. Researchers can use genetics to
determine how closely related parent birds are and thus how inbred each
chick is. The higher the level of inbreeding, the more closely related a
chick’s parents are.

FIGURE 3.2: An adult song sparrow (right)
feeding a much larger cowbird chick (left).

FIGURE 3.3: Cowbirds lay their eggs
in the nests of many species. Here is
a cowbird egg in the nest of an
eastern phoebe.
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FACTORS AFFECTING POPULATION SIZE ACTIVITY 3
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Song sparrows sometimes have their nests parasitized by the Brown-headed
Cowbird. Cowbirds, unlike most bird species, do not build their own nests.
Instead, females lay their eggs in the nests of other bird species, called hosts,
and leave all parental care up to these hosts. Species that rely on hosts to raise
their offspring are called brood parasites. For the host bird, accepting a
cowbird egg and rearing a cowbird chick can be very costly because cowbird
chicks typically outcompete the host’s offspring for food, and the host’s
offspring may starve. Additionally, when female cowbirds lay their eggs, they
sometimes eject one or more host eggs from the nest.
In birds, nesting success is essential for population growth to occur. Nesting
success refers to how many chicks are hatched and successfully raised in
one season, per nest. Researchers on Mandarte Island have tracked eight
variables, shown in Table 3.1, that help them analyze nesting success for the
song sparrows.

TABLE 3.1: Variables that May Affect the Nesting Success of Song Sparrows on
Mandarte Island

CLASS VARIABLE
Abiotic (non-living) Total rainfall during the nesting period (in mm)
Biotic (living) Minimum temperature (in degrees C)
Breeding density
Individual bird Local parasitism rate (the likelihood of the nest being
characteristics parasitized by cowbirds)*
Brood parasitism rate (the level of harm to nesting
success if the nest is parasitized by cowbirds)*
Female age
Level of inbreeding
Lay date

* A helpful analogy for understanding these two variables is to think of a disease. You may have
a small or large chance of getting a disease. If you do get the disease, the effects may be mild or
severe. You may have a small chance of getting a disease, but if you do get it, the effects may be
large—or you may have a high chance of getting a disease, but the effects might be minor. Any
combination is possible.

3. With your partner, review the information in the first two columns of
Student Sheet 3.1, “Predictions of Nesting Success in Song Sparrows
on Mandarte Island.” In the third column, record your predictions of
how you think each variable might affect the nesting success of song
sparrows, if at all, and whether the effect will be large, medium, small,
or none.

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

4. Visit the SEPUP SGI Third Edition page of the SEPUP website at
www.sepuplhs.org/high/sgi-third-edition. Follow your teacher’s
instructions for accessing the simulation, which is based on real data
collected by researchers.

5. With your partner, use the simulation to test your predictions from
Step 3.

• Test the effect of individual variables, starting with the variables you

predict have the greatest effect on nesting success.

• Test combinations of variables to see which result in higher and

lower probabilities of nesting success.
Keep track of your results on Student Sheet 3.1.
6. With your partner, analyze your data from Student Sheet 3.1 to

determine the combination of factors that results in the highest and
lowest probabilities of nesting success. Discuss why you think these
results might occur. Be prepared to share your ideas.

Build Understanding

1. Figure 3.4 is the population graph from Activity 1 for the song sparrow
population on Mandarte Island. Using as much evidence as you can
from the simulation in this activity, explain (a) what might be
happening to cause the changes in the population of sparrows, and (b)
what the carrying capacity might be for this population. Support your
ideas with evidence and reasoning.

200

Number of song sparrows 160

120

80

40

0 1979 1981 1983 1985 1987 1989 1991 1993 1995 FIGURE 3.4: Song sparrow
1977 population on Mandarte Island
Year over time

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LabAids SEPUP SGI Ecology 3e
Figure: Eco3e SB 01_07

FACTORS AFFECTING POPULATION SIZE ACTIVITY 3

2. If you were a wildlife manager whose job it was to increase the carrying
capacity of song sparrows on Mandarte Island, what would you try?
Explain your reasoning.

3. The song sparrows on Mandarte Island, an isolated population, have
been well-studied for decades, providing a great deal of data and a
deep understanding of different factors affecting the population. What
types of challenges would scientists face in doing this type of in-depth
research on other types of species in different environments, such as
the yellow perch from Activity 1?

4. Issue connection: Look again at the yellow perch graph in Activity 1.
Describe what is happening to the population size. If you were
managing this fishery, what data would you want to collect that is
similar to the data collected on the song sparrows? What other types of
data would you want to collect?

KEY SCIENTIFIC TERMS

abiotic
biotic
brood parasites
inbreeding

Extension

Birds are one of the most studied groups of animals in ecology for several
reasons, for example:

• Most birds are diurnal (active during the day), so they are convenient to

observe and study by people, who are also diurnal.

• Most birds fly and are easy to see and catch in nets.
• They appear in virtually all habitats—from polar regions to the desert,

from the seashore to 210 m below sea level.

• Birds respond relatively quickly to environmental changes, so they can

alert scientists to potential environmental problems.

• Many amateur birders and others who take a special interest in birds can

contribute useful information to scientists and environmentalists.

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ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

What have you observed about birds where you live? Consider keeping
track of the birds around you in a journal and seeing how bird populations
in your area change during the year. Visit the SEPUP SGI Third Edition
page of the SEPUP website at www.sepuplhs.org/high/sgi-third-edition
to learn more about how you can participate in studies of birds through
citizen science projects. Perhaps you will join the 60 million birdwatchers
in the United States!

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4 Scaling Up: Ecosystems

Investigative Phenomenon

In the previous learning sequence, you
explored individual populations of
organisms and factors affecting them.
Populations are part of ecosystems that
include many kinds of organisms. The song
sparrows are part of the Mandarte Island
ecosystem, which also includes cowbirds
and many other organisms. Coral reefs are
another type of ecosystem. Imagine a coral
reef in your mind. Which of the photos in
Figure 4.1, all of coral reefs, most
closely resembles what you
imagined? What similarities and
differences do you notice among
the different reefs? What factors
do you think could contribute to
these differences? In this
learning sequence,
you will explore
factors that explain
some of the
differences among
ecosystems.

FIGURE 4.1: Coral reefs can
be many different shapes,
sizes, and colors.

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ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

In the previous activity, you investigated data collected from a bird
population on an isolated island. Scientists can define that ecosystem
easily: It’s the island. But what happens when an ecosystem is not isolated?
How can researchers define what that ecosystem is? How can an
understanding of an isolated ecosystem be applied to other, less isolated
ecosystems? In this activity, you will explore how four different types of
ocean ecosystems can be defined.

Guiding Question

What defines an ecosystem?

Materials

FOR EACH STUDENT

Student Sheet 4.1, “Ecosystem Comparisons”

Procedure

1. Read the following text box about the crosscutting concept of systems
and system models, and discuss with your partner how you think this
concept relates to ecosystems.

A system is an organized group of related components that form a
whole.
A system model specifies the components within the system and
how the components interact with one another. It must also specify
the boundary of the system being modeled, defining what is
included in the model and what is considered external.

2. Follow your teacher’s instructions for determining which of the four
ecosystems your group will explore.

3. With your group, read the information about the ecosystem you are
investigating. Use Student Sheet 4.1, “Ecosystem Comparisons,” to
take notes on the following factors for your ecosystem:

• Components: Abiotic and biotic factors that are important in your

ecosystem

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SCALING UP: ECOSYSTEMS ACTIVITY 4

• Interactions: Relationships between different components of your

ecosystem

• Boundaries: Limits to your ecosystem; how it is divided from other

ecosystems

• Scale: The relative size of your ecosystem

Ocean Sunlight Zone

Oceans cover more than 70% of the earth and FIGURE 4.2: These fish live in the ocean sunlight zone.
contain more than 97% of the earth’s water. whales and sharks, and many smaller vertebrate
Scientists divide the ocean into different layers, species, including fish, sea birds, and sea turtles.
or zones. The zone above 200 meters in depth is The majority of marine fisheries rely on fish that
considered the sunlight zone. Below this depth, live in the sunlight zone.
the amount of light drops significantly. The
ecosystem occupying the sunlight zone is the Invertebrates account for over 95% of the
most extensive ecosystem on Earth. It begins animal species found in the ocean. These include
where the shallow coastal waters surrounding crustaceans (shrimps, crabs, etc.), mollusks
all the continents end, and it extends outward (clams, octopuses, etc.), and sea jellies (jellyfish).
through the rest of the oceans’ surfaces. Abiotic The sunlight zone is also home to tiny organisms
conditions, such as light, temperature, salinity, called plankton, which are carried along ocean
and circulation, in the ocean sunlight zone are currents. One drop of ocean water can contain
fairly consistent at any given location. hundreds of these organisms, most of which are
too small to see with the naked eye.
Approximately 10%–15% of the known species
on Earth are found in the sunlight zone, but this
accounts for 90% of all marine (ocean) life. Many
unique types of organisms in the ocean are not
found on land. In fact, the ocean is more diverse
than land with regard to major groups of
organisms. Several groups of animals are found
only in the ocean, including sea stars (starfish),
sea urchins and their relatives, comb jellies, acorn
worms, and trumpet worms. Other animals in
the ocean include extremely large species, such as

sea level

sunlight zone

Sunlight rarely penetrates beyond this zone.

herring Chinook
orca salmon
200 meters

FIGURE 4.3: The ocean sunlight zone refers to the top 200 m of the ocean.

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SGI Ecology 3e
Figure: SGI3e Eco SB 4_6

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

Coral Reefs

Coral reefs occupy less than 0.1% of the ocean’s either rock or the dead skeletons of corals,
area, about 285,000 km2, yet they are home to building up the reef structure over time. Many
over 25% of all marine species. Because of the coral colonies can live for hundreds or
tremendous diversity of life found on reefs, they thousands of years. Most reef-building corals
are sometimes called the “rainforests of the have algae living in their tissues. The corals and
ocean.” Coral reefs tend to be found in relatively algae have a mutualistic relationship: The coral
shallow, warm water in the tropics, at latitudes provides the algae with a protected
between the Tropic of Capricorn and Tropic of environment, and in return the algae produce
Cancer. However, some coral species have oxygen and nutrients that the coral can use for
evolved to live in deeper, colder water. its own needs. This relationship, which evolved
millions of years ago, has allowed coral to live in
Coral reefs get their name from the organisms nutrient-poor water.
that form the physical foundation for the coral
reef ecosystem. Reef-building corals are tiny Coral reefs are one of the most diverse
colonial animals that produce a hard outer ecosystems in the world. In addition to the
skeleton of limestone. This skeleton attaches to nearly 1,000 species of hard coral that form the

reefs, the reefs are home to tens
of thousands of other species,
including hundreds of soft corals;
invertebrates, such as sea
cucumbers, anemones, sponges,
jellies, and octopuses; and
vertebrates, such as sea turtles
and sea snakes. Reefs also
provide food, safety, and
spawning areas for at least 4,000
different species of fish.

FIGURE 4.4: Many organisms live in and among
coral reefs.

FIGURE 4.5: Coral reefs are made of the hard
outer skeleton of individual coral polyps.
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SCALING UP: ECOSYSTEMS ACTIVITY 4

Intertidal Zone

All marine shorelines around the world longest period of time. Some intertidal zones
experience tides. The intertidal zone is the area are large, stretching for hundreds of meters
of the shoreline that is exposed to air at low tide from the shore, while others are isolated and
and covered with seawater at high tide. Some narrow and extend less than a meter from shore.
intertidal zones are rocky and may have shallow
pools of water remaining in depressions in the All the organisms that inhabit the intertidal
rocks during low tide. Others are sandy, with no zone are marine species who have adapted to
standing water during low tide. Intertidal zones living in this continually changing environment.
can be divided into sub-zones depending on FIGURE 4.6: The tidal zone is subdivided into
how long the sub-zone is exposed to air; the several zones, depending on how long the zone is
upper sub-zone is the area exposed for the exposed to air when the tide is out.

spray zone

high tide zone

middle tide zone A-31
low tide zone

SGI Ecology 3e
Figure: SGI3e Eco SB 4_11
MyriadPro Semibold

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

Intertidal Zone continued

The algae that live here have adapted to being found in the lower part of the zone, which is
exposed to air or being underwater for long usually submerged in water. Organisms found
periods of time. Many kinds of invertebrates in the middle of the zone include mussels,
are found in this zone. Barnacles are often crabs, and anemones.
found in the upper part of the zone (with the Twice a day at low tide, intertidal organisms
greatest exposure to air). Sea stars are typically may be exposed to air for many hours. They
may also experience large
changes in other abiotic factors,
such as temperature and sunlight.
Most intertidal animals feed only
when in water. Many also use
oxygen dissolved in water rather
than from air. Thus, they are at
risk of starvation and suffocation
during low tide. Animals living
permanently in the intertidal
zone have evolved a variety of
adaptations that enable them to
survive in this challenging
habitat.
At low tide, intertidal
organisms are exposed to
predation by land animals (such
as gulls). At the same time, low
FIGURE 4.7: This rocky tide pool contains many organisms, tide allows them to escape
including ochre sea stars and sea anemones. predation by marine animals

that cannot survive in the
intertidal zone (such as fish), or
by animals that can’t live in the
upper part of the intertidal zone
(such as sea stars).

FIGURE 4.8: Mangrove forests grow
in the intertidal zones near the
equator.
A-32

SCALING UP: ECOSYSTEMS ACTIVITY 4

Humpback Whale Respiratory Microbiome

Humpback whales are large marine mammals may play an important role in fighting off
found in oceans and seas around the world. Like infections and otherwise maintaining the
all whales, humpbacks have adapted to living in whale’s overall health.
water, yet rely on breathing air to get oxygen
and expel carbon dioxide. Whales don’t have Scientists are only beginning to investigate
noses like most mammals; instead, they have a the importance of the humpback’s respiratory
blowhole on the top of their heads that connects microbiome, but one thing is becoming clear:
to their lungs. Humpbacks breathe through this Humpback whales may be 16 meters long, but
blowhole when the top of their head breaks they still benefit from providing a home for
through the surface of the water. The blowhole their microscopic hitchhikers!
is kept closed by muscles when the humpback is FIGURE 4.9: Many organisms, including humans
under water. When a humpback exhales air out and humpbacks, rely on microorganisms to
of its blowhole, a spray can often be seen. This maintain their health.
spray is a mixture of seawater and the exhaled
contents of the humpback’s lungs. FIGURE 4.10: As humpback whales surface to breathe,
they expel a spray. Scientists have studied the contents
Scientists have known for years that whales’ of this spray and learned that humpback respiratory
respiratory systems are a common site for systems contain complex microbiomes.
bacterial infections. But only recently, by
studying the spray from humpbacks’
blowholes, did scientists discover that many
species of bacteria and other microbes live in
the respiratory system of
healthy whales. In fact, a core
group of bacteria can be
found in the respiratory
system of healthy whales who
live in different oceans. This
core group of bacteria is a
microbiome, a specific group
of microorganisms found in a
particular environment—in
this case, the whale’s
respiratory system. Similar to
the human gut microbiome
(the group of microorganisms
found in your stomach and
digestive tract), each whale’s
microbiome is unique to the
individual whale, depending
on many factors. Which microorganisms are
present can indicate the health of the whale,
and scientists believe that the microbiome

A-33

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

4. Follow your teacher’s instructions for sharing information about your
ecosystem with your class.

5. In your science notebook, sketch a model for one of the four
ecosystems from this activity. Include the ecosystem components
(biotic and abiotic), interactions, and boundaries in your model. Be
sure to clearly label everything.

6. With your group, return to the information on the crosscutting
concept of systems and system models in Step 1. Using this
information, create a definition of an ecosystem. Be prepared to share
your definition with your class.

7. Follow your teacher’s instructions to come to a consensus as a class on
the definition of an ecosystem.

Build Understanding

1. Why is it necessary for researchers to specify the boundary of the
ecosystem they are investigating?

2. Suppose you were a scientist developing a model for the Mandarte
Island ecosystem and the song sparrows. Would it be easier to identify
the components, interactions, and boundaries of this ecosystem than
others? Why or why not? What challenges might you have?

3. Issue connection: How could understanding the components,
interactions, and boundaries of a fishery’s ecosystem help scientists
monitor the sustainability of that fishery?

4. Figure 4.11 shows are three images taken of the same coral reef at FIGURE 4.11: a. Reef seen
different scales. Explain what types of factors researchers might from a distance. b. Reef
investigate if they want to monitor the carrying capacity of the reef with several species of
ecosystem at the scale shown in the photo on the left (a), in the middle coral and other
(b), and on the right (c). organisms. c. Individual
coral polyps that make
Hint: Consider what types of components and interactions might be up the coral reef.
studied at these three scales.

a b c
A-34

SCALING UP: ECOSYSTEMS ACTIVITY 4

5. Look again at the coral reef photos at the start of this activity. What
might explain the similarities and differences you observed in these
coral reefs?

Extension: Engineering Connection

Studying large ocean animals such as whales poses a lot of challenges.
Studying the spray from when they exhale might seem impossible, but a
group of researchers developed a very clever method to study the spray of
humpback whales. Scientists used small drones to follow the whales and then
fly over them as they surfaced, capturing the whale’s spray with a special
device attached to the drone. The analysis of samples collected using this
method led to the discovery of the whales’ respiratory microbiome.

Visit the SEPUP SGI Third Edition page of the SEPUP website at
www.sepuplhs.org/high/sgi-third-edition to learn more about this
study and what the scientists learned from it.

KEY SCIENTIFIC TERMS

boundary
component
ecosystem
interaction
scale
system
system model

A-35



5 Patterns of Biological Diversity

i n t h e l a s t ac t i v i t y , you saw that ecosystems can exist on many
scales. While ecosystems all have common features, they also have
differences. Some ecosystems contain more species than others. Some
have more of a particular type of organism. Why do you think these
differences occur? Why might it be important for scientists to understand
these differences? In this activity, you will explore patterns of species
diversity for different groups of organisms on larger scales—globally and
across the United States—and you will consider factors that might lead to
these patterns.

Guiding Question

What patterns of biological diversity occur for different
groups of organisms, and what might cause these patterns?

Materials

FOR EACH GROUP OF FOUR STUDENTS

Vertebrate Diversity Map
set of five Abiotic Factor Maps

Procedure

Part A: Global Coral Diversity

1. With your group, look at the map of coral diversity in Figure 5.1. Use
what you learned about coral reefs in the previous activity to discuss
which abiotic factors may help to explain this pattern. Write your
explanation in your science notebook, and be prepared to explain your
scientific reasoning with the class.

A-37

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

588

<50
Species
FIGURE 5.1: Global coral diversity
LabAids SEPUP SGI Ecology 3e
Figure: Eco3e SB 05_01

MyriadPro R2e. gW9.i5t/h11your group, look at the map of ocean temperature at the surface
around the world in Figure 5.2. Discuss how well you think this abiotic
factor explains the pattern of coral diversity.

c7 m0 y0 k9 c0 m42 y92 k0 c100 m0 y20 k70 c25 m0 y15 k90

Maps1 Maps2 Maps3 Maps4 Maps5

c0 m30 y70 k0 c0 m43 y94 k0 c15 m10 y0 k85 c95 m50 y30 ko c15 m90 y90 k0

c60 m30 y100 k0 c50 m20 y75 k0 c15 m90 y90 k0 c90 m55 y40 k0 c39 m7 y12 k0

c15 m10 y0 k85 c80 m0 y0 k55 c12 m7 y0 k0 c0 m0 y0 k6 c25 m0 y15 k90

>F4IG80U0RmE 5.2: Ocean surface temperature

3000 - 4800 m
1800 - 3000 m

12A0-03-81800 m

600 - 1200 m
300 - 600 m

PATTERNS OF BIOLOGICAL DIVERSITY ACTIVITY 5

FIGURE 5.3: Ocean depth

3. Repeat Step 2 for the map of ocean depth in Figure 5.3.
4. Based on your discussions in Steps 2 and 3, revise your explanation in

your science notebook from Step 1. Be prepared to share your revised
explanation with the class.

Part B: Vertebrate Groups in the United States

5. Follow your teacher’s instructions for determining which groups of
vertebrate organisms you will investigate (reptiles, amphibians, birds,
or mammals), and obtain the Vertebrate Diversity Map for that group.

6. With your group, read about your vertebrate group and study the map.
Where is your vertebrate group most diverse? Where is it least diverse?
Based on what you read about your vertebrate group, what ideas do
you have about this pattern? In your science notebook, record your
initial ideas about what factors might explain the patterns you see in
the map.

7. Obtain a set of five Abiotic Factor Maps. With your class, review the
Elevation and Topography Map and compare it to the Vertebrate
Diversity Map for your organism.

A-39

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

8. Each person in your group should take one of the remaining four
Abiotic Factor Maps, study it, and decide whether this factor might be
important in explaining the patterns in species diversity for your
vertebrate group. Record your ideas in your science notebook.

9. With your group members, take turns sharing information about the
factor that you examined. As a group, decide whether each factor
might be important in explaining the distribution of your vertebrate
group in the United States.

10. Discuss with your group what might account for the patterns you
observed, based on all the factors that you considered. Be prepared to
share your ideas with the class.

Build Understanding

1. For the group of vertebrate organisms that you examined:
a. Write an explanation that can account for the pattern of species
distribution. Be sure to discuss all the factors and to use data from
the maps to support your explanation.
b. How did your explanation change as you examined more factors?
c. Imagine that you were looking at the map for your vertebrate
group but on a global scale—like the coral maps you examined.
Would you expect to see the same patterns of species distribution
in other locations in the world? Why or why not?

2. Select one other vertebrate group that you learned about in the class
discussion. Compare and contrast the distribution of that vertebrate
group with yours. What might account for any differences in the
distribution of the two vertebrate groups?

3. Look again at the coral reef photos at the start of Activity 4: Scaling Up:
Ecosystems. Use what you’ve learned in this activity to explain the
differences you see in these photographs.

4. Issue connection: Do you think species diversity is important in
ecosystems? Is it something that scientists should consider when they
are thinking about fisheries’ sustainability? Why or why not?

KEY SCIENTIFIC TERMS

biological diversity

A-40

6 Producers and Consumers

i n e a r l i e r l e a r n i n g s e q u e n c e s , you looked at patterns in
ecosystems on different scales. Now you will look at what patterns can
indicate about interactions between organisms. In this learning sequence,
you will explore the feeding relationships between different organisms in
an ocean food web and how these relationships allow matter to cycle and
energy to flow through the ecosystem. What types of challenges do you
think organisms like the Southern Resident orcas, shown in Figure 6.1,
face in their effort to survive?

FIGURE 6.1: Southern Resident orcas (Orcinus orcas)

A-41

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

Investigative Phenomenon

The Southern Resident orcas (Orcinus orcas) when orcas were no longer being hunted or
have long been a symbol of the Pacific captured. This is also the year that scientists
Northwest. They are often spotted hunting for started studying this population. What
their preferred food, Chinook salmon, in the patterns do you notice in the graphs? What
Salish Sea near the northwest coast of do these patterns make you wonder about
Washington. Resident orcas spend their entire this population?
lives with their family units in the same
geographical area. This population of Resident Since 2005, this population of whales has
orcas is an extended family group, comprising been protected as an endangered species in
three social subgroups called pods. the United States. What patterns do you
notice in the graphs after 2005? Do these
Prior to the early 1970s, over 50 orcas were patterns look like any of the patterns you
removed from this population due to observed in Activity 2: Population Growth
hunting and capture for captivity in marine Models? What factors do you think might be
parks. Figure 6.2 shows the count of whales causing these patterns?
in each pod in the population since 1976,

Population count (number of whales) 110 JKL Population (CWR)
100 L Population (CWR)
J Population (CWR)
90 K Population (CWR)
80
70
60
50
40
30
20
10

0
1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025
Year

FIGURE 6.2: Southern Resident orca population, J, K, and L pod census as of July 1 each year
(Center for Whale Research)

A-42
LabAids SEPUP SGI Ecology 3e
Figure: Eco3e SB 06_02
MyriadPro Reg 9.5/11

PRODUCERS AND CONSUMERS ACTIVITY 6

Guiding Question

How can you determine an organism’s role in a food web
from the organism’s physical features?

Materials

FOR EACH GROUP OF FOUR STUDENTS

dropper
15-mL dropper bottle of methyl cellulose
graduated cup of water containing live plankton
prepared slides of plankton
set of Orca Food Web cards
set of Plankton cards

FOR EACH PAIR OF STUDENTS

microscope slide with a well
coverslip
microscope

FOR EACH STUDENT

Student Sheet 6.1, “Orca Ecosystem Model”
Student Sheet 6.2, “Classifying Plankton”

SAFETY

Always carry a microscope properly with both hands—one
hand underneath and one hand holding the microscope arm.
Because you are working with live organisms, wash your hands
thoroughly with soap and water after completing the procedure.

Procedure

Part A: Plankton in the Ocean Ecosystem

1. Work in your group of four to use the set of Orca Food Web cards to
build a food web with the organisms on the cards. A food web is a
diagram of the relationships within an ecosystem, showing how each
organism derives the energy and matter required for survival. Discuss
your ideas about the feeding relationships between each of the
organisms. Record your ideas by developing a food web on Student
Sheet 6.1, “Orca Ecosystem Model.” Be prepared to share your group’s
food web with the class.

A-43

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

Hint: Remember that the arrows in a food web point toward the
organism that is doing the “eating,” as shown in Figure 6.3 from a
different ecosystem.

FIGURE 6.3: Simple food web

2. Use the guidelines in “Using a Microscope” in Appendix B to remind FIGURE 6.4: Placing a
you ho3w299toSEPpUrPoSpGeI ErcloylougysSeE your microscope to observe plankton. coverslip on a slide

3. Use theAFiggdeurnreod:ap32Mp9e9edErCcootSnoBd09p7/_l9a0.53ce a drop of water containing live plankton into
the well of a microscope slide.

4. If your teacher directs you to, add one drop of methyl cellulose to the
drop on the slide.

5. Carefully touch one edge of the
coverslip to the water, at an angle as
shown in Figure 6.4. Slowly allow the
coverslip to fall into place. This should
prevent trapping of air bubbles under
the coverslip.

6. CadejnutsetrtthheemsliicdreossocotpheatstehtteinwgesllaissndeirceecsstlayryA3Fo2i.ggv9eu9enredSr:Ea3Pt2MUh9eP9edESCclGooiIgSnEBdhco09t6l/o_9og.05yp3SeEning, and
7. Begin by observing the sample on the lowest objective lens. You may

need to search the slide to find specimens, and they may move across
your field of view.
8. Sketch at least two different organisms that you observe.
9. With your partner, discuss your observations of the two organisms you
observed.
10. Follow your teacher’s instructions for looking at the prepared plankton
sides with the microscope.

A-44

PRODUCERS AND CONSUMERS ACTIVITY 6

11. Begin by observing the plankton at the lowest level of magnification,
and increase the magnification, if necessary, until you have the best
view for observing the overall structure of the organism but can also
see structures inside or on the surface of the plankton.

Note: Use only the fine-focus knob for a medium- or high-
magnification setting to avoid breaking the slide.

Part B: Classifying Plankton

12. There are many different species of plankton in the ocean ecosystem.
Share with your partner the similarities and differences between the
two organisms that you observed. Did you notice any specialized
features? What did they look like or remind you of?

13. With your partner, examine the drawings of plankton in Figure 6.5.
What specialized features do you notice?

euglena

rotifer

copepod

oscillatoria

diatoms closterium volvox stentor

1SFiE4gP.uU rUeP:sSEeGcoISEStcBuo0dlo6eg.0ny5tSSBh3eeet 6.2, “Classifying Plankton,” to classify each FIGURE 6.5: Drawings of
plankton you observe as either a producer or a consumer based on plankton showing
their specialized structures. A producer is an organism that produces specialized features
its own food. A consumer is an organism that gets its food by eating
other organisms.

Hint: Most of the plankton you will see are multicellular organisms, but
you might also see some single-celled plankton on your slide.

A-45

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

15. Follow your teacher’s instructions for examining the Plankton card set
and sorting them into two groups: plankton that produce their own
food, called phytoplankton, and plankton that consume other
organisms for food, called zooplankton.

Build Understanding

1. What is the relationship between phytoplankton and zooplankton in
the ocean ecosystem? Explain your ideas, using your observations of
the structures in the two organisms as evidence.

2. What is the role of phytoplankton in the orca’s food web? Explain,
using information from this activity. If needed, revise your model on
Student Sheet 6.1 to incorporate your new ideas.

3. Why do you think that most (90%) of marine life lives in the euphotic
zone, the uppermost layer of the ocean that is exposed to intense
sunlight?

4. Biomass is the mass of organisms living in a given area or ecosystem at
a given time. The biomass of phytoplankton is approximately 1% of the
total biomass on Earth. What do you think the role of phytoplankton is
in the global ecosystem? Explain, using information from this activity.

5. In 2018, the governor of Washington assembled a task force of
concerned stakeholders, including federal, state, local, and tribal
partners, to make recommendations for policies and activities that
would help the Southern Resident orcas. One goal identified by the task
force was to increase the amount of Chinook salmon in the fishery.

One of the group’s recommendations was for the governor to fund a
program that closely monitors the zooplankton population in the areas
where these orcas live. Why do you think the group made this
recommendation? Explain your ideas, using the food web you created
in this activity.

6. Issue connection: Think about how humans interact with the orca
food web. What role do humans play in this food web? Do you think
people should be included as part of the ocean ecosystem?

A-46

PRODUCERS AND CONSUMERS ACTIVITY 6

KEY SCIENTIFIC TERMS

biomass
consumer
energy
fishery
food web
matter
producer

Extension

One way that scientists monitor the amount of phytoplankton in the open
ocean is to use satellites. Chlorophyll, found in phytoplankton, can be
detected by instruments on satellites that orbit Earth. Figure 6.6 shows a
satellite map of the average chlorophyll concentration in oceans around the
world from July 2002 to May 2010.

FIGURE 6.6: Map of chlorophyll concentrations in global oceans

Describe any patterns you observe in the concentration of phytoplankton
in the global oceans in Figure 6.6. Why do you think the global population
of phytoplankton is closely monitored by scientists? Explain your ideas.

A-47



7 T he Photosynthesis and
Cellular Respiration Shuffle

i n ac t i v i t y 6, yo u co n s i d e r e d the differences between

phytoplankton (producers) and zooplankton (consumers) and the roles they
play in ocean ecosystems. In this activity, you will investigate the interactions
of plankton and other organisms in the Southern Resident orcas’ food web
on a different scale: inside the cells of organisms. You will investigate how the
cellular processes of photosynthesis and cellular respiration drive the cycling
of matter and allow energy to flow in the ecosystem.

Organism Organ system Organ Tissue Cell Organelles
(digestive system)

Shoot
system

Root
system

Organism Organ system Organ Tissue Cell Organelles
(digestive system) A-49

SGI 3e SB Fig 7.1

FIGURE 7.1: Levels of organization in an animal and a plant

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

How does energy drive the cycling of matter in an
ecosystem?

Materials

FOR EACH PAIR OF STUDENTS

set of Photosynthesis and Cellular Respiration cards
set of Photosynthesis and Cellular Respiration captions

FOR EACH STUDENT

completed Student Sheet 6.1, “Orca Ecosystem Model,” from Activity 6
colored pencils

Procedure

1. Read the following text.

Photosynthesis is the process of carbon dioxide and water reacting to
produce glucose and oxygen in the presence of light energy from the
Sun. Glucose is a sugar, a sweet substance that can be broken down to
release energy. Cellular respiration is the process by which an
organism’s cells use glucose (C6H12O6) and oxygen (O2) to produce
water (H2O) and carbon dioxide (CO2) and to release energy that can
be used for life functions, such as movement and growth. These
cellular processes determine how matter—the stuff that makes up all
living and nonliving things—cycles between organisms and
ecosystems, and how energy—the ability to cause objects to change,
move, or work—is involved.

2. Add the following to your food web model on Student Sheet 6.1, “Orca
Ecosystem Model”:

• Your ideas about how matter is cycling among producers and

consumers in the food web. Include carbon dioxide, water, oxygen,
and glucose in your drawing.

• Your ideas about where cellular processes involving energy are

happening and how energy is flowing among organisms in the
food web.

A-50

THE PHOTOSYNTHESIS AND CELLULAR RESPIRATION SHUFFLE ACTIVITY 7

3. Obtain the Photosynthesis and Cellular Respiration cards. Each card
represents a stage in the cellular processes of photosynthesis or
cellular respiration. With your partner, sort the Photosynthesis and
Cellular Respiration cards into two groups: cards that describe stages
of photosynthesis and cards that describe stages of cellular
respiration. As you sort, use what you already know about these
cellular processes and what you see on the cards. Record your
groupings in your science notebook.

4. Work with the other pair in your group to compare your card sorts.
Discuss the similarities and differences between the ways each pair
sorted the cards. Decide together how to sort each group of cards in a
way that you all think is most scientifically accurate. Record any
changes from your initial groupings in your science notebook.

5. Check your ideas against the key provided by your teacher to ensure
that you have the cards sorted correctly.

6. Obtain a set of Photosynthesis and Cellular Respiration captions from
your teacher and lay them out on the table.

7. Read each one aloud and decide if the caption describes a stage in
cellular respiration or a stage in photosynthesis.

8. Match each caption with one of the Photosynthesis and Cellular
Respiration cards.

9. Return to your model on Student Sheet 6.1, and revise it based on what
you learned in this activity. In your revised model, be sure to include
all of the following:

• Where cellular respiration and photosynthesis are happening
• How matter (carbon dioxide, water, oxygen, and glucose) is cycling

in the ecosystem—where it is coming from and going to

• How energy is flowing in the food web—where it is coming from

and going to
To help illustrate your ideas, you can use colored pencils, symbols,

and/or words. As needed, refer to the text in Procedure Step 1 and the
Photosynthesis and Cellular Respiration cards and captions to help
you revise your model.
10. Share your revised model with your partner and discuss the similarities
and differences between your models. Make additional revisions to
Student Sheet 6.1, based on what you and your partner discussed.

A-51

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

Build Understanding

1. What is the relationship between the cellular processes of
photosynthesis and cellular respiration?

2. Use information from your completed Student Sheet 6.1 to write an
explanation about how matter is cycled and energy flows among the
organisms in an ecosystem. Be sure that your explanation includes:

• how the cellular processes of photosynthesis and cellular respiration

are involved

• how matter (carbon dioxide, water, oxygen, and glucose) is cycling

in the ecosystem

• how energy is flowing in the ecosystem

3. Issue connection: In late 2013, a large mass of warm seawater with less
nutrients than normal moved into the area where the Southern
Resident orcas live. Scientists named this warm water mass “The Blob.”
The Blob increased the surface water temperatures 14ºC (6ºF) until
2016. Warm water with fewer nutrients slows the growth rate of
phytoplankton. During the years that The Blob was in the area,
scientists monitoring the Chinook salmon fishery caught so few
salmon compared to other years
that they thought there were
holes in their nets.
a. Why do you think The Blob
had this effect on the
Chinook salmon population?
b. What effect do you think the
decrease in the salmon
population could have had on
the Southern Resident orcas?

FIGURE 7.2: Map showing the warm water mass—“The Blob” —off
the Pacific Coast of Canada and the United States

KEY SCIENTIFIC TERMS

cellular respiration
consumer
photosynthesis
producer
sugar

A-52

8 Life in the Dark

i n 1977, s c i e n t i s ts t h o u g h t co m p l e x ecosystems without

sunlight were impossible. That’s because most producers use energy from the
Sun to photosynthesize. The ocean ecosystems that you have investigated so
far have been in the euphotic zone, the uppermost layer of the ocean that is
exposed to intense sunlight. Is it possible for producers to exist in the deep
ocean in the absence of sunlight? In this activity you will go back in time to
learn about a discovery that stunned the scientific community.

DISTANCE SUNLIGHT TRAVELS IN THE OCEAN

sea level sunlight (euphotic) zone

herring Sunlight rarely penetrates beyond this zone.

200 meters orca Chinook
salmon

twilight (dysphotic) zone

Sunlight decreases rapidly with depth.
Photosynthesis is not possible here.

sword sh

hatchet sh shrimp

1,000 meters giant squid midnight (aphotic) zone

tripod sh Sunlight does not penetrate at all.
This zone is bathed in darkness.

angler sh

FIGURE 8.1: The ocean is divided into different zones based on how much light
SreGaIcEhceosloitg. y 3e
Figure: SGI3e Eco SB 8_1
MyriadPro Reg/Semibold 7/9.5/11

A-53

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

How do ecosystems without sunlight get the energy and
matter needed for the system to survive?

Materials

FOR EACH STUDENT

3–5 sticky notes

Procedure

1. Read the text that follows. As you read, use the Read, Think, and Take
Note strategy:

• Stop at least three times during the reading to mark on a sticky note

your thoughts and questions. Use the guidelines below to start your
thinking.

Read, Think, and Take Note: Guidelines

As you read, use a sticky note from time to time to:

• Explain a thought or reaction to something you read
• Note something in the reading that is confusing or unfamiliar
• L ist a word from the reading that you do not know
• Describe a connection to something you’ve learned or read

previously

• Make a statement about the reading
• Pose a question about the reading
• Draw a diagram or picture of an idea or connection

• After writing a thought or question on a sticky note, place it next to

the word, phrase, sentence, diagram, drawing, or paragraph in the
reading that prompted your note.

• After reading, discuss with your partner the thoughts and questions

you had while reading.

A-54

LIFE IN THE DARK ACTIVITY 8

Reading FIGURE 8.2: Alvin
research submersible
In 1977, a team of marine geologists, geochemists, and geophysicists set
out on a research vessel to investigate the deep ocean floor near a A-55
mid-ocean ridge called the Galápagos Rift in the Pacific Ocean. Based on
evidence gathered from previous expeditions, the scientists expected to
find hydrothermal vents along the mid-ocean ridge, which would provide
evidence to further develop the theory of plate tectonics. Hydrothermal
vents are underwater hot springs that form due to volcanic activity.
To explore the ocean floor, the geologists on the research expedition used a
remote-operated vehicle called ANGUS (Acoustically Navigated
Geophysical Underwater System). ANGUS was built to travel to depths of
20,000 feet (6,100 m) underwater and was equipped with strobe lights and
a camera to illuminate the complete darkness and take pictures of the deep
ocean. As ANGUS completed its first dive, the camera took thousands of
pictures of the ocean floor, which indicated that there was a hydrothermal
vent, as expected. The pictures also revealed hundreds of clams and
mussels living around the vent. The scientists were shocked by this
discovery of life. No one had considered that life—let alone entire
ecosystems—could exist in places without the sunlight necessary for
photosynthesis. Additionally, the hot and volatile underwater volcanic
environment was believed to be too harsh for life to thrive. The geologists
would have turned to their biologist colleagues for help in understanding
these mysterious organisms, but finding life at these depths of the ocean
was so unexpected that no biologists were part of the research team.
The next day, a team of scientists dove to the area
in a research submersive vessel called Alvin,
where they viewed the first hydrothermal vent
and the giant clams and mussels living around it.
Soon after, the team found four more
hydrothermal vents nearby. At each vent, they
found life flourishing where hot, mineral-rich
water was spewing out of the sea floor. These
conditions were toxic or inhospitable to most
organisms found on Earth’s surface. Scientists had
lots of questions: How were these organisms
surviving here? How did the organisms interact
with other organisms in this ecosystem? What
did each organism eat? What was driving the flow
of energy in this ecosystem that existed in
complete darkness?
The geologists weren’t equipped to begin
answering these questions on this initial voyage.

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

However, they did make one important additional discovery: When they
retrieved a sample of the hot water spewing out of the vent, it was full of
hydrogen sulfide. This proved to be an important key in unlocking the
puzzle of how these newly found ecosystems operate. On subsequent
voyages to study the hydrothermal vents, biologists brought along
specialized equipment that they designed to collect a few of the organisms
and gather data about them. This equipment attached to Alvin allowed
them to bring the specimens back up to the surface for further
investigation.
From their data collection and analysis, biologists determined that the
foundation of these ecosystems was bacteria and archaea. Archaea are
single-celled organisms that resemble bacteria but are genetically distinct.
Analysis of samples taken near the hydrothermal vent showed that the
biomass of bacteria and archaea in these environments was over 330 times
greater than deep ocean water sampled from 2,400 m below the surface,
and over 3 times greater than the productive surface ocean water. This
productive bacteria and archaea population is what was providing the food
supply for various consumers living near the vent, such as zooplankton and
crabs. Further study revealed that the bacteria and archaea also have
mutually beneficial relationships with many organisms near the vent, such
as tube worms and clams, that ensure the survival of both organisms. These
organisms provide food for the vent consumers at the top of the food web,
such as octopuses and ratfish.

FIGURE 8.3: Giant tube worms (Riftia pachyptila) at a hydrothermal vent.
A-56

LIFE IN THE DARK ACTIVITY 8

Bacteria and archaea in and around FIGURE 8.4: Hydrothermal vent
hydrothermal vents are the producers
of the ecosystem, yet they do not
conduct photosynthesis in the
darkness of the ocean floor. They
conduct a cellular process called
chemosynthesis. Chemosynthesis
differs from photosynthesis in that the
energy needed for the organism to
produce its own food is released from
chemical reactions, not from sunlight.
In chemosynthesis, bacteria and
archaea use inorganic compounds
(like hydrogen sulfide or methane)
captured from the environment in
chemical reactions that transfer energy
and recombine the matter into organic
compounds, such as sugars like
glucose. The organism then uses the sugars to release energy for life
functions through cellular respiration, or the sugars are used later when
these organisms become prey for another organism.

Different bacteria can use different molecules to release energy. Many
bacteria near the hydrothermal vents release energy when they combine
the hydrogen sulfide from the vent water with oxygen and carbon dioxide
from the seawater to produce glucose, sulfur, and water. In some areas of
the hydrothermal vent environment, the seawater is almost entirely
depleted of dissolved oxygen. Scientists found that bacteria living in this
area of the vent are able to use different chemicals to conduct
chemosynthesis and produce sugars in the absence of oxygen.

Before the discovery of hydrothermal vents and their unique ecosystems,
scientists did not know that the energy flow and matter cycling in an
ecosystem could be driven by processes other than photosynthesis. This
discovery led to new questions about how life could take hold in
environments without adequate oxygen or sunlight. Scientists from all
disciplines asked new questions about the origins of life on our planet, the
life that could exist on other planets, and if life could take hold in places
previously designated as inhospitable.

A-57

ECOLOGY SCIENCE & GLOBAL ISSUES: BIOLOGY

Build Understanding

1. Return to the explanation you wrote in Build Understanding item 1 in
Activity 7. Revise your explanation of how matter is cycled and how
energy flows among organisms in an ecosystem, adding what you
learned in this activity about hydrothermal vent ecosystems.

2. How could the rate of a producer’s photosynthesis or chemosynthesis be
an indicator for the overall health of an ecosystem? Explain your ideas.

3. Identify at least two similarities and two differences between how
matter cycles and energy flows in the hydrothermal vent ecosystems
and the Southern Resident orca ecosystem.

4. For the first 1.2 billion years of life on Earth, there were no organisms
that could photosynthesize. What might a food web have looked like
during that time?

5. Using what you learned about system models in Activity 4: Scaling Up:
Ecosystems, define the hydrothermal vent ecosystem. Be sure to identify
its components, interactions, and boundaries.

6. What effects do you think people may have on these seemingly isolated
ecosystems?

KEY SCIENTIFIC TERMS

chemosynthesis
energy
matter
photosynthesis

Extension

Deep-sea exploration requires contributions from many types of
scientists as well as engineers. Visit the SEPUP SGI Third Edition page of
the SEPUP website at www.sepuplhs.org/high/sgi-third-edition to read
articles about and view videos of deep-sea organisms, communities, and
geological features.

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