Download Life Science Unit

BSCS Middle School Science
Student Edition
levels of organization in the biosphere
Life Science Unit:
biosphere–the part of Earth that
contains life
ecosystem–Chesapeake Bay
Living Energy
community–all organisms in
Chesapeake Bay
population–all striped bass in
Chesapeake Bay
organism–striped bass
energy
energy
energy
flows to
flows to
organ system–circulatory
systemflows to
organ–heart
sunflower
tissue–muscle
pocket mouse
bull snake
cell
Tablecell–blood
of Contents
large molecule–hemoglobin
Chapter 2: Ecosystems
and Energy................ LS2-2
molecule–water
Engage: Get Out!....................................................................... LS2-4
Explore: Backyard Biology.........................................................LS2-7
Explain: The Web of Life........................................................... LS2-11
Elaborate: Stability and the Web of Life................................... LS2-22
Evaluate: Evaluate: Menu Connections................................... LS2-28
Spanish Vocabulary................................................................. LS2-31
atom–hydrogen
LS2-1
BSCS Middle School Science
Student Edition
Life Science Unit · Living Energy
chapter 2:
Ecosystems
and Energy
A
re you curious about all the different kinds of living things around you?
Dogs, squirrels, trees, butterflies, or maybe even bacteria? All these
different living things can be exciting yet overwhelming. But using a few
“big ideas” from science can help you start to see patterns in living systems. Some
of these patterns relate to energy and matter: (1) energy is not created or
destroyed, but instead changes form and (2) the amount of matter that goes into
a system is the same as the amount of matter that leaves a system. Two big ideas!
In chapter 2, Ecosystems and Energy, you’ll use scientific inquiry and these two
powerful ideas to help you understand the living world. You’ll also work on the
teamwork skill of making sure that everyone understands.
Goals for the Chapter
By the end of this chapter, you should be able to
n
explain how energy transfers in ecosystems affect organisms;
n
begin to describe how matter cycles in an ecosystem;
n
summarize the roles different organisms play in an ecosystem;
n
use food webs to make predictions about changes in ecosystems; and
n
gather your own data from where you live, contribute your data
to a class data set, and develop an explanation of your findings.
Fortunately, you have help meeting these goals. Each activity in this chapter
gives you experiences to learn about important ideas related to ecosystems and
energy. The activities are as follows:
Engage—Get Out!
Explore—Backyard Biology
Explain—The Web of Life
Elaborate —Stability and the Web of Life
Evaluate—Menu Connections
Remember that chapter organizers can help you keep track of where you are in
your learning. Look at the chapter organizer every day.
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Engage—Get Out!
key idea: Finding patterns in
the natural world begins with
careful observations.
Linking Question:
How does the mass of
animals in an area relate to
the mass of plants?
Ecosystems
and Energy
major CONCEPTS
• Food webs show the
energy relationships in
an ecosystem.
• Energy pyramids help explain
patterns in ecosystems.
• Changes to 1 species
affect other organisms
in a food web.
Linking Question:
How is my life affected
by the web of life?
Elaborate—Stability and
the Web of Life
key idea: Changes in a
population affect parts of the
web of life.
Explore—Backyard Biology
key idea: Evidence shows how
the mass of plants relates to
the mass of animals.
Linking Question:
How can understanding
matter and energy
help explain patterns in
the world?
Evaluate—Menu
Connections
key idea: Everyday life depends
on connections between
organisms in the web of life.
Explain—The Web of Life
Part I: Organizing Life
Part II: Matter and Energy
in the Web of Life
key idea: Food webs track
matter and energy in
ecosystems. Transfers of
energy help explain patterns
in the numbers of different
kinds of organisms.
Linking Question:
How can changes in
1 population affect a
food chain?
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Engage
Get Out!
How can you start to make sense of the living world? A good place to start is just
by looking. In this Engage activity, Get Out!, you’ll make some careful observations
of your local area and then some other places in the world. Then you’ll describe
the ideas you have that might explain some of the patterns you observe.
Many important questions in science got their start with someone simply
observing living things. Then the person started to wonder, “How can I explain
what I just saw or heard?” These simple and fun steps started the person on the path
of scientific inquiry. Start observing!
Materials
For each student
paper clip or sticky note
Caution
Do not handle any organism you observe, even if you are certain it is harmless. Unnecessary handling may be harmful to the organism and yourself.
Process and Procedure
1.Go outside with your classmates. Look around you. In your science notebook,
write a brief description of the area.
This is a new chapter. Did you start on a new page in your science
notebook? Did you label the new chapter?
Your description of the area should be specific. Think about the
following questions. Are you in a park? Next to a city street? In the
country? What time of day is it? What are the weather conditions?
Careful observations help you recall what you observed. They also
help you reflect on your observations later.
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Engage
2.Observe the area for 2 minutes, focusing on observing as many different living
things as you can. You may want to make some notes about what you are
seeing, but do not let that take too much time out of your 2 minutes. After 2
minutes, sketch and label the organisms you saw.
It’s easy to overlook living things that you see all the time. Now
is the time to look closely. Make sure to include potted plants,
grass in a field, weeds in a parking lot, squirrels in trees, crows
perched on a trash can, insects crawling under rocks, and so on.
Do not be afraid to dig in the soil! Look at the ground where the
plants meet the soil. Each of your drawings should be about a
quarter of a page. Put something in each diagram to indicate
the size of the organism.
3.Make a quick estimate of the relative number of living plants, animals, and
fungi. Use symbols such as greater than (>), much greater than (>>), less than
(<), much less than (<<), or equal to (=) to compare the 3 groups. Record your
estimates in your science notebook.
You may have questions about what counts as an individual.
Make sure you write down in your science notebook what you
think counts as an individual. Don’t forget that organisms like
insects and worms are animals. Also, some plants may lose their
leaves during certain parts of the year but are still alive.
You may also wonder what counts as fungi. An example of fungi
is mushrooms.
4. Return to your classroom. On your own, answer the following questions:
Suppose you could collect all the living things in the area. You separate them
into plants, animals, and fungi. Which group do you think would have the most
matter (or, the most mass)? Why do you think that way?
Remember, this is an Engage activity. You’re not expected to know
all the right answers. But sharing your best ideas now makes it
easier to learn as you go through the chapter.
5.Make a 3-column table. Label the first column “ecosystem.” Label the second
column “number of plants compared to the number of animals.” Label the
third column “Which group has the most matter?”
6. Look at photos from different ecosystems on Earth. Fill in the table as you see
each photo.
To fill in the second column, make a quick estimate of the number of
individual plants and animals. Is the number of plants greater than
(>), less than (<), or equal to (=) the number of animals? Of course
there will be animals and plants that are hard to see in the photo.
You’ll have to use what you know to make a reasonable guess.
To fill in the third column, do the following. Suppose that you collect
all the living things in the photo. Which group do you think would
have the most matter: plants or animals? Think about weighing
each group to determine which you think would have more matter.
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Engage
7.Compare your table from Step 5 to your partner’s table. Can you come to a
consensus on your answers?
A consensus means you both agree. Discuss each row of the
table. If you find you had different answers, explain why you chose
the answer you did. Then see if you can agree on 1 answer.
Reflect and Connect
Answer the following questions on your own in your science notebook. As you
learned in other chapters, it is important to write down your best ideas during an
Engage activity even if you don’t know the complete answer now. Mark this page
with a paper clip or sticky note. You will revisit your answers to Questions 3 and 4
later in the chapter.
1.Were the numbers of plants and animals in the different areas (including your
local area) similar or different? Explain your answer.
2.You looked at different areas and predicted if animals or plants had the most
matter. Was there a pattern in your predictions among these different areas? For
example, was one group always larger than the other? Explain your answer.
3.Humans can eat lots of different kinds of organisms. We do not often eat animals that eat other animals, like wolves, lions, or orcas. Why do you think these
animals are not a regular part of what humans eat?
4.You often see plants. Think about the number of individual grass plants in a
field. It is much less common to see large carnivores like alligators, wolves, or
mountain lions. Why do you think this is so?
5.Why do you think bacteria and other microscopic organisms were left out of
your analysis?
6. Which do you think are more important to human survival: plants or animals?
Why do you think that?
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Chapter 2 · Ecosystems and Energy
Explore
Backyard Biology
In the Engage activity, you made rough estimates about plants and animals in
different areas on Earth. What if you dig a little deeper into your own neighborhood? Could the things you are learning apply to the places you see every day?
Work with your class to discover patterns in your own world.
Materials
For each student
1 yellow plastic bowl (cereal-bowl size)
1 piece of string, 1 m long
1 stake or nail (optional)
1 copy of Backyard Biology Data Collection Protocol handout
1 cup of water
2 tsp of salt
liquid dish detergent
1 plastic containers with screw lids
1 pair of scissors
1 plastic grocery bag
gallon-sized, resealable plastic bags (optional)
1 paper clip or sticky note
For each team of 2 students
hand lens or stereomicroscope (dissecting microscope)
paper towels
different-colored pens or pencils
For the class
4–8 electronic balances or triple-beam balances
Caution
Do not directly touch any organism you observe, even if you are certain it is harmless. Touching organisms may be harmful to them.
The Explore activity, Backyard Biology, is adapted with permission from Richardson, M. L., &
Hari, J. (2008, April). Teaching students about biodiversity by studying the correlation between
plants and arthropods. American Biology Teacher, 70(4), 217–220.
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Chapter 2 · Ecosystems and Energy
Explore
Process and Procedure
In this activity, you will collect insects, plants, and other organisms from a local
area. You will only collect a small number of insects, but they will not survive.
If you do not want to participate in this part of the activity, please inform
your teacher.
Data Collection
1.Write the following focus question in your science notebook. Draw a thick box
around it.
a
Focus Question: “How does the mass of plants in an area compare to
the mass of small animals like arthropods?”
A simple way to think about mass is that it’s the amount of “stuff,”
or matter, that something has. Mass is not the same thing as
weight, but they are related.
Arthropods are a group of animals. There are many different
Corel
species of arthropods. Scientists have named over 1 million
species. Still, many biologists believe there may be over 10 million
b
different species! The arthropod group includes insects and
spiders. It also includes crustaceans like crabs and pill bugs
(figure 2.1).
2.In this activity, you will collect the plants and arthropods from an area near
where you live. Use what you know and your experience from the Engage
activity to make a prediction. Write the following sentence in your science
notebook. Choose the correct phrase from those in the parentheses. Then fill
Corel
in the blank with your reason.
“I think the mass of plants in an area will be (higher than / lower than / the same
as) the mass of the small animals because
c
.”
3.Look again at the focus question from Step 1. How could you test this question?
Discuss your ideas with a partner.
4.Contribute your ideas to a class discussion about designing an experiment to
test the focus question.
5. Take notes as you learn how you will collect data for this investigation.
6.Get the materials you need, including a copy of the Backyard Biology Data
Collection Protocol. Read through the protocol. Ask your teacher to clarify any
steps you don’t understand.
7.Take the materials home. Complete all the steps in the protocol. As part of the
protocol, you will put the arthropods in a plastic bottle and the plants in a bag.
Tomorrow or the next day, bring the plastic bottle back to school. Write a note
Corel
Figure 2.1: Arthropods. There are
many different kinds of arthropods.
Pictured here are (a) an insect
(rhinoceros beetle), (b) a spider
(hunting spider), and (c) a pill bug.
You will collect arthropods in
this activity.
so you don’t forget!
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Chapter 2 · Ecosystems and Energy
Explore
After Data Collection
8.
Join with a partner to examine the arthropods you collected. Use the
following steps.
a. Individually, pour a small amount of your sample back into the
yellow bowl.
b. Use a hand lens or a stereomicroscope to examine the sample.
Place any arthropods you find onto a paper towel. It might be helpful
to use forceps to remove the smallest insects.
c. When you have removed all the organisms from the bowl, dump
the remaining fluid down the sink.
our more of your sample into the yellow bowl. Repeat Steps
d. P
8a–c until you have removed all the organisms.
e. Use the paper towel to dry off the organisms as best as you can.
9.Create a 2-column table in your science notebook. Label the first column “mass
of small animals.” Label the second column “mass of plants.”
10.Using a balance, find the mass of the arthropods you collected. Then find the
mass of the plants you collected. Multiply the mass of the plants by 4. Record
these values in the first row of your table. Label this row “my values.”
You only collected plants from one-fourth of the circle around the
bowl. This is considered your sampling area. Multiply the mass of
the plants by 4 to estimate the mass for the whole area in the circle
with a 1-meter (m) radius.
11.Contribute your data to a class data set. Record the average mass for small animals
and plants in the second row of your table. Label this row “class averages.”
12.Create a bar graph in your science notebook. The y-axis should be “mass
(grams).” You should have 4 bars along the x-axis. Two bars will be for your
samples. The other 2 bars will be for the class averages. Add a title to your graph.
13.Use the Identify and Interpret (I2) strategy to help make sense of the graph. To
use this strategy, follow these steps.
a. Look for patterns on your graph. Draw an arrow to all the patterns
that you identify.
b. Write “What I see” followed by a short phrase describing what you
identified. Be concise and write only the highlights of what you see.
c. Interpret what you see, 1 observation at a time. Write “What it means”
below each “What I see” phrase. Then describe what you think the
observation means.
d. Write a caption for the graph. Make sure that you describe how the
graph helps you answer the focus question, “How does the mass of
plants in an area compare to the mass of small animals like arthropods?
For more information about this strategy, see I Can Use the Identify
and Interpret (I2) Strategy.
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Chapter 2 · Ecosystems and Energy
Explore
14. Exchange graphs with your partner. Look over your partner’s graph. Give your
partner feedback on his or her graph. Use the following questions to help you
give good feedback.
n
Is the y-axis properly spaced?
n
Does the graph have a title?
n
Are the bars on the graph labeled?
n
Does the caption answer the focus question?
n
Does the caption include evidence?
n
Does the caption include a claim and reasoning?
15. Make revisions to your graph and your I2 phrases. Use feedback from
your partner if you found it useful. Use a different-colored pen or pencil for
your revisions.
You do not have to use all the advice your partner gave if you do
not think it is useful. However, you should consider all the advice
and make a decision about which pieces to use.
Reflect and Connect
Answer these questions on your own. Also mark the page with a paper clip or sticky
note. You’ll revisit your answers later in the chapter.
1.In Step 2, you made a prediction about how the mass of plants in an area
compares to the mass of animals. Did your experimental results match
your predictions?
2.Suppose you compare your results with a classmate’s. Your classmate found
that the mass of plants in an area was higher than the mass of animals. How
could you explain this evidence?
3. The plants and animals you examined are made of matter. What do you think
is the source of most of the matter that makes up the animals?
4.
Look at the chapter organizer. The key idea from the Engage activity is:
“Finding patterns in the natural world begins with careful observations.” The
key idea from this Explore activity is: “Evidence shows how the mass of plants
relates to the mass of animals.” Write your own linking question to tie these
activities together.
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Chapter 2 · Ecosystems and Energy
Explain
The Web of Life
All living things are connected to other living things. What does this mean? For
starters, some organisms eat other organisms. Still other organisms—like plants—
need the nutrients that come from the decomposed bodies of other organisms. All
organisms need energy and matter.
We call the connections among living things the web of life. You are a part of
the web of life. You depend on a large number of other organisms. Think about
how many living things contributed to your breakfast! Also, did you know that
thousands of different species of bacteria live in and on you? These bacteria help
your body with important tasks! In this Explain activity, The Web of Life, you will
investigate the web of life. You will use what you learn to help you answer some of
the questions you encountered in the first two activities.
Part I—Organizing Life
Materials
For each student
different-colored pens or pencils
1 highlighter
Process and Procedure
1. Think of a local park or similar type of area.
a. Quickly write down in your science notebook at least 6 living
organisms that you would see.
b. Write down 4 nonliving things you’d expect to find.
2.Sort your list of organisms into at least 3 different groups based on some
characteristics of the organisms. Each organism can only be in 1 group. Draw 1
circle for each group you create and write the names of the organisms in the
circle. Do not write the characteristics you used.
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Chapter 2 · Ecosystems and Energy
Explain
3.
Exchange your circles of living organisms with a partner. Then complete
Steps 3a–d.
a. Look over the groupings your partner created.
b. Try to guess what characteristics your partner used to sort
the organisms.
c. Go through a few rounds of guessing if you don’t come up
with the correct answer.
d. D
iscuss with your partner the reasons you grouped the
organisms together.
4. Work with your partner to answer the following questions.
a. Do you think one way of sorting the organisms was better than the
other? Explain.
b. In what ways do you think sorting the organisms on Earth into
different groups is helpful to scientists? In other words, what kinds of
problems or questions might this help them solve?
5.
In the last few steps, you organized living things in different ways. Read
Organizing the Web of Life to help you understand different ways that scientists
organize living things. As you read, enter all bold and unfamiliar terms into
your personal glossary. Also complete the tasks described in the reading.
Reading: Organizing the Web of Life
Biologists study all kinds of questions. They use what they learn to solve
lots of different kinds of problems. But living systems have many levels
of organization (figure 2.2). Let’s take a look at some of the levels,
starting with the smallest and least complex. At the smallest level are
microscopic things like molecules and cells. As you get to more-complex
levels, you start to find structures you can see with just your eyes, such
as organs. Your heart is an example of an organ. Even more complex
are individual organisms, like you!
In chapter 1, you studied populations—that’s another level. A
population is all the individuals from one type of organism in an
area. A species includes all the populations of one type of organism.
An individual from one species usually cannot reproduce with an
individual from another species.
What if you included all the different living species in an area? Then you
have a community. An ecosystem includes both the living community
and the nonliving part of the environment.
L
ook back to the living and nonliving parts of the environment
you listed in Step 1 of Process and Procedure. You started
describing an ecosystem.
continued
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Chapter 2 · Ecosystems and Energy
Explain
Some scientists even study the whole biosphere. The biosphere is the
portion of Earth where life is found. As you go up the levels, they
become complex. This represents one way to group different parts of
living systems—by levels of organization.
levels of organization in the biosphere
Figure 2.2: Levels of structure
in the biosphere. The living world
has increasing levels of organization.
Each higher level depends on the one
below it.
biosphere–the part of Earth that
contains life
ecosystem–Chesapeake Bay
community–all organisms in
Chesapeake Bay
population–all striped bass in
Chesapeake Bay
organism–striped bass
organ system–circulatory system
organ–heart
tissue–muscle
cell–blood cell
large molecule–hemoglobin
molecule–water
atom–hydrogen
Another way scientists organize living things is based on how closely
related they are to other species. A crow is more closely related to a pigeon
than it is to a dog. All the birds are in one group. Scientists use evidence to
figure out which species are more closely related to other species.
Another way to organize living things is by how they get the matter and
energy they need to live. Think about two big groups. One group
includes organisms that make their own food. The other group includes
organisms that need to eat other organisms.
Producers make their own food. Producers include plants, algae, and
some bacteria. Producers use light energy to help them form food,
which is a type of chemical energy. Remember photosynthesis?
Energy is not turned into food. Instead, energy is used to make
new forms of matter from other forms of matter. For example,
plants can combine carbon dioxide and water to form sugar.
If you’re not sure how plants and other producers make food,
review how photosynthesis works using the reading Making
More Algae in chapter 1.
continued
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Chapter 2 · Ecosystems and Energy
Explain
Consumers are organisms that rely on other organisms for energy. You
are a consumer. Dogs are consumers. Insects are consumers. Consumers
generally eat other plants or animals. They break down the matter from
the things they eat to get the energy they need to live.
Decomposers are a very important group of consumers. They break
down the bodies of dead animals, plants, and all other organisms. Some
decomposers use waste (like feces) from other organisms as a source of
energy. Mushrooms, other fungi, and many bacteria are decomposers.
Placing organisms in one of the two groups is usually a good way to begin
separating species. Ask yourself, “Do they make their own food?” If so,
they are producers. Do they eat other organisms for food? If so, they are
consumers. But we can further organize living things. Examine figure 2.3.
This diagram represents a food chain. A food chain summarizes the
feeding relationships among different groups of organisms in a community. It shows who eats whom. The arrows in a food chain represent the
direction of energy transfers. They point from the organism that gets
eaten to the one doing the eating. Because energy transfers from the plant
to the mouse, the arrow points toward the mouse.
energy
flows to
sunflower
energy
flows to
pocket mouse
energy
flows to
bull snake
red-tailed
hawk
Make a simple food chain that includes at least three organisms.
Include different organisms from the ones in figure 2.3. Pay
Figure 2.3: A simple food chain.
In this food chain, energy gets
transferred from the sunflower to
the pocket mouse to the bull snake
to the red-tailed hawk. Notice the
direction of the arrows.
sunflower: USDA, Photo by Edward McCain
mouse: Photo by Cheryl S. Brehme, USGS
snake: U.S. Fish and Wildlife Service
hawk: Corel
special attention to the direction of the arrows.
Biologists use food chains to divide the consumers in a community into
more-specific groups. Producers are still just called producers. Herbivores
are organisms that only eat plants. Carnivores are consumers that eat the
herbivores. Other organisms that eat the carnivores are called secondary
carnivores, and so on. These levels for the consumers are called “trophic,”
or feeding, levels. Organisms that eat at more than one level are called
omnivores. For example, many people eat both plants and animals,
making them omnivores.
What about decomposers? They are included as consumers, but things can
get complicated. Decomposers can function as herbivores when they break
down dead plants. The same decomposer can function as a high-level
carnivore when it breaks down the bones of a carnivore. To keep their role
clear, decomposers usually get their own level in a food web.
continued
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Chapter 2 · Ecosystems and Energy
Explain
Food chains are pretty simple. But real ecosystems are more complicated.
There are lots of organisms, and they interact in many ways. For
example, red-tailed hawks eat snakes, but they may also prey on mice
that eat seeds. Lots of connected food chains form a food web (figure
2.4). A web shows the relationships among different feeding levels.
Examine the diagram of a food web for a marine community in figure
2.4. Food webs can be very complex, and this one shows only some of
the main players.
Figure 2.4: A marine food web.
Food webs are a collection of
multiple food chains. They
summarize the flow of energy in
an ecosystem. Are you starting to
understand why it is called the
web of life?
orcas
seal
Sun
king crab
sea otters
fish
seabirds
sea urchin
zooplankton
krill
kelp
phytoplankton
Complete the following tasks related to figure 2.4.
• Identify the producers in this food web.
• Find three ways to trace the energy transfers from
the Sun to an orca.
• Find at least four food chains.
Food webs help scientists understand how living things interact.
The web of life summarizes all the interactions among all living things.
One thing that ties all organisms together is the need for nutrients
and energy. Understanding the movement of matter and energy in
ecosystems is the big idea for this chapter.
n
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Chapter 2 · Ecosystems and Energy
Explain
6.Review the glossary entries and the food chain developed by your partner.
Offer helpful feedback on the entries. Revise your own entries after
reviewing the feedback from your partner by using a different-colored pen
or pencil.
7.Prepare to observe a demonstration of a food web by making a 2-column
table in your science notebook. Label the left-hand column “What I
observed.” Label the right-hand column “What it means.”
8. Watch the demonstration. Fill in the table as you watch or play a role in
a simulation.
If you were a part of the simulation, write down your observations
as soon as the demonstration is over. You may need to ask a
partner to help you remember all the parts of the demonstration.
9.Copy the analogy map in figure 2.5 into your science notebook. Fill out the
table with as many parts of the demonstration as you can remember. Add
extra rows if needed.
Figure 2.5: An analogy map.
Fill in this map so you can better
understand the demonstration.
Feature of the
demonstration
is like …
Feature of a real food web
They are alike because …
String
is like …
the transfer of energy
the string showed who eats
whom, and that is how energy
gets transferred.
energy from the Sun
A candy bar or
hard candy
10.In your science notebook, draw the food web you saw in the demonstration.
Use this food web as a base to complete Steps 10a–c.
a. Add at least 3 more organisms to your food web.
b. Add mushrooms and bacteria to your food web as decomposers.
c. Use a highlighter to trace energy transfers leading to the wolf in
2 different ways.
Stop and Think—Part I
Answer the following questions on your own in your science notebook.
1. Deer are herbivores. Some deer have a parasite called a tapeworm. A parasite
lives in or on another organism and uses it as a source of food, but it usually
doesn’t kill the host. Where would you place parasites in a food chain?
2.Examine figure 2.4 again. Predict if the following populations would increase or
decrease if the number of orcas were much lower. Explain your predictions.
a. Sea otters
b. Sea urchins
c. Kelp
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Explain
3.Food webs are often a simpler version of the large number of interactions that
actually exist in a community. Why do you think biologists use food webs to
study communities?
Part II—Matter and Energy in the Web of Life
Materials
For each student
different-colored pens or pencils
You just learned a way to summarize energy relationships in a community. It’s called
a food web. Now you can use what you learned to start explaining other patterns in
ecosystems—patterns you investigated in the Engage and Explore!
Process and Procedure
1.Some unusual questions are below. Write your best ideas about the following
questions in your science notebook. Work by yourself as you answer the
questions. You’ll learn more about them later and will have a chance to revise
your work.
a. Much of the matter in living things has the element carbon. Imagine
that you eat a steak. The cow that was the source of the meat ate
mostly grass. Could some of the carbon in grass end up in the cells
of your toe? Why or why not?
b. Could carbon that was a part of a long-dead dinosaur be part of
a dog living today? Could that carbon be a part of you? Explain
your answer.
c. Wolves started living with humans about 10,000 years ago. Could
you drink a particle of water that a wolf drank 10,000 years ago and
eliminated as urine? Explain.
2.Discuss your answers with a partner. Make any revisions to your answers in
a different color.
3.To help you answer these questions, read What’s the Matter? As you read,
complete the tasks described in the reading. Write your answers in your
science notebook.
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Chapter 2 · Ecosystems and Energy
Explain
Reading: What’s the Matter?
Here is a simple rule about matter. The amount of matter going into a
system is the same as the amount of matter leaving a system. Under
normal circumstances, matter does not usually turn into energy. If we
think about the whole Earth as a system, we realize that not much
new matter is being added to the system. Well, maybe an occasional
meteorite, but that is about it. And matter is not leaving the system.
What does this mean? It means that the matter on planet Earth cycles
on and on and on.
What about living systems? Living things are made up of matter.
You may realize that the matter that forms your body comes from
the food and liquids you ingest. As a consumer, your food comes from
other organisms. But what about producers? How does matter from
the nonliving environment enter producers? The matter that makes up
producers like plants becomes a part of the plant in different ways.
One key process is, again, photosynthesis. Producers use carbon in
the air to help them make food and other structures. Other matter
producers need, like nitrogen and water, comes from the soil. Plants
get this matter through their roots. So producers bring matter into
living systems from the nonliving environment. Some of this matter
is returned directly to the nonliving world by plants. For example,
plants release oxygen to the air. But luckily for you, some of the matter
goes to other living things.
Draw a picture of a plant in your science notebook. Label this
drawing “matter in an ecosystem.” Leave room to add more
drawings. In your drawing, show where the matter in the nonliving
world comes from to build the plant. Then show some of the
matter going back to the nonliving environment from the plant.
Matter can also move through a food chain. In figure 2.3, matter moves
from the sunflower to the mouse. The mouse returns some matter to the
nonliving environment. For example, the mouse breathes out carbon
dioxide. But the matter in the mouse can also be eaten by a snake. Are
you starting to get the picture?
Add an herbivore and a carnivore to the picture of the plant you
started. Use arrows to show the direction matter is moving through
the food chain. Also indicate where matter gets returned to the
nonliving environment.
In summary, matter cycles through organisms and the nonliving world.
Matter can pass through many different food chains. At other times, it
can be part of the nonliving environment.
n
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Explain
4.Compare your drawing of matter moving through a food chain to a drawing
that your teacher will show you. Make revisions to your drawing as needed.
5.Revisit the answers you gave to the questions in Step 1. Make revisions to your
answers based on your new understanding.
6.In the Explore activity, you examined the mass of the plants and the arthropods
in an area. You tried to explain this observation in Reflect and Connect
Question 2 of that activity. Review your answer to this question to help you get
ready for Step 7.
7.Read Energy in Ecosystems. As you read, make a new drawing in your science
notebook and label it “energy in an ecosystem.” This drawing should include
the following.
a. Show the Sun and a food chain.
b. Include at least 3 levels and the forms of energy in the system.
c. Use arrows to indicate the direction of energy transfers.
d. Show how energy enters the food chain. Label this “energy in.”
e. Also show how energy leaves the living system. Label this “energy out.”
Reading: Energy in Ecosystems
You’ve learned that matter cycles in ecosystems. But what about energy?
Let’s look at two important ideas about energy. First, energy cannot be
created or destroyed. But it can change to other types of energy. This
means organisms cannot make their own energy. Second, when energy
changes types, some energy always changes into heat. Heat eventually
leaves living systems and escapes out into the universe. So if energy
always leaves the system, this means that living systems need to replace
that energy. In other words, living systems always need a source of energy.
So what happens to energy in a food chain? Almost all the producers
on Earth change light energy from the Sun into chemical energy. They
use this chemical energy to do all the things they need to do to live
and grow. The herbivores then eat the food (chemical energy) in the
producer. They use this chemical energy to do all the things they need
to live.
All the energy from the producers is not available to the herbivores.
Some parts of the producers may not be eaten by consumers. As a
result, these parts are available to decomposers. Also, when plants
change energy from one form to another, some energy is converted
into heat. The heat leaves the living systems. And don’t forget that
some of the energy is used by the producers to grow. In the end,
continued
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Explain
you should see that there is less energy available to the herbivores than
there is to the producers.
Next are the carnivores. Do you think they have more or less energy
available to them than the herbivores have?
Answer this question in your science notebook. Then quickly
check with a partner to see if your partner got the same answer.
Figure 2.6 is a diagram biologists use to summarize the energy available
at different levels in an ecosystem. It is called an energy pyramid. Notice
that there is less energy available as you go “up” the food chain. A
general rule is that only about 10 percent of the energy from one feeding
level is available at the next level. This number varies in different
ecosystems. Where does the “lost” energy go? You now know that
much of this energy is lost to the universe as heat.
Figure 2.6: An energy pyramid.
What happens to energy as it passes
through a food chain? Notice that
there is less energy (measured in
kilocalories, or kcal) as you go “up”
the food chain.
toplevel
carnivores
carnivores
herbivores
producers
10 kcal
100 kcal
1,000 kcal
10,000 kcal
So what does all this mean? It means that energy gets transferred in
living systems. It also means that much of the initial energy gets turned
into heat. As a result, ecosystems need a constant source of energy.
This is another big idea.
Understanding energy and matter also helps us explain a pattern in
the living world. What happened when you took the mass of all the
producers in an area and compared it to the mass of the animals?
continued
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Explain
You did this in the Explore activity. The mass from the producers
was much higher. Why? Because there is less energy available to the
herbivores. All organisms need energy to help form their bodies, but
herbivores have less energy available compared to plants. Now think
about the herbivores compared to the carnivores. The amount of
matter in the herbivores is higher than the mass of all the carnivores.
Can you figure out why? Decreasing amounts of energy at higher
feeding levels helps explain why large predators are relatively
uncommon and why they have less total mass.
n
8.Compare your drawing of energy transfers in a food chain to a drawing that
your teacher will show you. Make revisions to your drawing as needed.
9.Revise your previous explanation from Reflect and Connect Question 2 in the
Explore activity. Use what you learned about matter and energy in ecosystems.
Reflect and Connect
Work by yourself to answer the following questions. Write your answers in your
science notebook.
1.Imagine that a fifth grader says to you, “I understand how plants relate to
energy. Plants make the energy they need out of nothing.” Do you agree with
the student? Answer this question by writing a short dialogue between you
and this other student. Your dialogue might look like lines from a play.
2.Look back in your science notebook to your answers to Reflect and Connect
Questions 3 and 4 from the Engage activity. Revise your previous answers given
your new understanding. Remember, your goal is to have an answer with all the
information you now know.
3.Which took more energy to produce—a pound of corn or a pound of chicken?
Explain your answer.
4. How can energy be a limiting factor for a population of consumers?
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Chapter 2 · Ecosystems and Energy
Elaborate
Stability and the Web of Life
Remember learning about how populations grow? You did this in the previous
chapter. You know that a small population of mice in a cage can’t grow forever.
Limiting factors can slow the growth of all populations. These factors can be
nonliving or living. In this chapter, you’ve explored how different organisms in a
community interact. All organisms are dependent on other organisms in one way or
another. In this Elaborate activity, Stability and the Web of Life, you’ll put these
ideas together as you explore how changing factors in one population affect other
species in a food chain. You’ll do this by exploring a simulation about grass, sheep,
and wolves. A simulation sure is easier than raising the sheep yourself!
Materials
For each team of 2 students
access to a computer and the Wolf Sheep Predation simulation
different-colored pens or pencils
Process and Procedure
1.Examine figure 2.7. This figure shows a simple food chain that you will
explore by using a simulation. Write the following focus question for this
investigation in your science notebook and put a box around it: “How can
a variable in one population affect other organisms in a food chain?”
Figure 2.7: A simple food chain.
In this food chain, grass represents
the producers, sheep, the herbivores,
and wolves, the carnivores. This is
a simple model. In reality, wolves
do occasionally prey on sheep, but
the main part of their diets is wild
herbivores such as deer or elk.
The number of domestic sheep lost
to wolf predation is usually less than
2 percent.
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Chapter 2 · Ecosystems and Energy
Elaborate
2.Predict how the organisms in the food web will affect one another. To do
this, choose the correct phrase in each set of parentheses, and then finish the
following sentences:
“When the amount of grass is high, the sheep population will probably
(increase / decrease / stay the same) because _____.”
“When the amount of grass is high, the wolf population will probably
(increase / decrease / stay the same) because _____.”
3.Discuss your predictions with a partner. Make revisions to your predictions
if needed.
4.Access the Wolf Sheep Predation simulation. Once you are on the opening
page, complete Steps 4a–c. Select Run Wolf Sheep Predation in Your Browser.
a. Move the slider in the Grass? box to On.
b. Move the speed slider at the top of the black box to the left. You will
have to experiment with different speeds to find one that works well
for your team.
c. Click on the Setup button. Your screen should look like figure 2.8.
Press setup after
you’ve changed
other settings.
Press go to both
start AND stop
the simulation.
These numbers at the
bottom right show the
setting for each variable.
Speed slider: moving this
bar to the left slows down
the simulation.
Figure 2.8: Wolf Sheep Predation
setup. Make sure to move the slider
for Grass? to On. Move the speed
slider to the left to find a speed that
works for your team. Then click
Setup. Look closely at the screen and
the descriptions of the different parts
of the simulation.
Make sure
to move this
slider to on.
You can see
the most
recent
population
values here.
Note the
grass no. is
divided by 4.
Wilensky, U. (1997). NetLogo Wolf Sheep Predation
model. http://ccl.northwestern.edu/netlogo/models/
WolfSheepPredation. Center for Connected Learning
and Computer-Based Modeling, Northwestern University, Evanston, IL.
A graph showing the populations of the 3 species over
time will be shown here. You can put the cursor on the
graph and get the x,y values at different points.
The teamwork skill you will focus on in this activity is making sure
that your partner understands. Especially when using computer
simulations, it can be easy for one partner to quickly move through
a number of changes on the screen while the other partner sits
passively. Throughout the activity, check in to make sure your
partner knows what is happening when you change one or more
parts of the simulation.
5.Read the Need to Know The Wolf-Sheep-Grass Simulation to yourself to help
you understand how the model works. Review each of the variables with
your partner to make sure you both understand what they mean.
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Elaborate
Need to Know: The Wolf-Sheep-Grass
Simulation
In the Wolf Sheep Predation simulation, you are exploring a simple model of
a food chain. The model was written with the following rules in mind:
1.Wolves and sheep wander around the area randomly. Sheep must eat
grass as a source of energy. Wolves must eat sheep as a source of energy.
2. Each time a sheep or wolf moves, it costs the animal some energy.
3. If a sheep or a wolf runs out of energy, it dies.
4.Each wolf and sheep that is alive at each time step (or tick) has a certain
chance of reproducing. Some will, and some won’t.
5. It takes a certain amount of time for grass that gets eaten to grow back.
You have the ability to change certain factors in the model. See figure 2.9 for
a summary.
n
Variable
Description
Initial-NumberSheep
This is the number of sheep at the beginning of the
simulation. This number can range from 0 to 250.
Sheep-Gainfrom-Food
This number tells you how much energy a sheep gets from
the grass it eats. This number can range from 0 to 50.
SheepReproduce
This number is the chance that an individual sheep
will reproduce at each time step. A higher number
means that more sheep will be born. It takes energy to
reproduce. This number can vary from 0% to 20%.
Initial-NumberWolves
This is the number of wolves at the beginning of the
simulation. This number can range from 0 to 250.
Wolf-Gainfrom-Food
This number tells you how much energy a wolf gets from
each sheep it eats. This number can range from 0 to 50.
Wolf-Reproduce
This number is the chance that an individual wolf will
reproduce at each time step. A higher number means
the same thing as a higher birthrate. This number can
vary from 0% to 20%.
Grass?
Grass can be removed from the model. If it is, you just
monitor how wolves and sheep interact. You should
start with the grass on.
Grass-RegrowthTime
This number is how fast the grass grows back after
being eaten by sheep. A higher number means the
population grows more quickly. This number can range
from 0 to 100.
Figure 2.9: A description of
the variables in the Wolf Sheep
Predation model.
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Elaborate
6.This simulation allows you to change many different factors (or variables).
Each variable might affect the 3 species in the community. Write down the
initial settings for the variables by using a table like the one in figure 2.10 as
a guide. Remember to multiply the grass population size by 4. You’ll learn
more about what these settings mean in later steps.
Variable
Initial setting
Figure 2.10: Variables in the Wolf
Sheep Predation simulation table.
Initial-Number-Sheep
Sheep-Gain-from-Food
Sheep-Reproduce
Initial-Number-Wolves
Wolf-Gain-from-Food
Wolf-Reproduce
Grass?
(Also include the amount of grass.)
On
Grass-Regrowth-Time
7.Do the initial settings for population sizes (initial number of sheep, wolves,
and grass) seem realistic to you? Explain why or why not. Make sure to refer
to the energy pyramid.
8. Try running the simulation by completing Steps 8a–b.
a. Run the simulation once with the initial settings (but with grass
turned on). Do this by pressing the Go button. Pressing the Go
button again will stop the simulation. Run the simulation until at
least 700 time steps (called “ticks”) have passed by.
b. The simulation may have gone by too quickly. Try sliding the speed
slider to the left. Try to get the timing so it takes about 10 seconds
to get to 350 ticks.
Start the model over by pressing the Setup button.
9.Run the simulation until about 350 ticks have passed by, and then pause it.
The person not in control of the computer should try to explain the patterns
on the graph to the partner.
10. Switch places so that the other person is in control of the computer.
Continue running the simulation until about 700 ticks have passed by. The
other partner should explain the patterns on the graph.
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Elaborate
11. Record the results from the simulation in your science notebook.
If approved by your teacher, you can print the graph by printing the
whole web page from within your internet browser. Make sure you
paste it in your science notebook. Otherwise, make a sketch of the
graph on your own.
12. Use the Identify and Interpret (I2) strategy to help make sense of your graph.
As you are observing what you see and deciding what you think
certain things mean, consider at least these questions. Are there
regular cycles? If so, how long does one cycle take? If there aren’t
regular cycles, describe why you think this is so.
13.Exchange graphs with your partner and add constructive comments to your
partner’s graph and I2 phrases and caption. Use the following questions to
help you give good feedback.
id your partner point out when certain populations went up
a. D
or down?
b. Did your partner describe how the sheep population affected
the grass population?
c. Did your partner describe how the wolf and sheep populations
affect each other?
14. Make sure that you each understand one another’s comments. Make revisions
based on the feedback you received, using a different color. Remember to at
least consider every piece of feedback you got.
15.Explore the effect of 1 factor or variable on interactions in this food chain.
Do this using the following steps.
ith a partner, decide which variable to test. Be sure to test
a. W
only 1 variable.
b. Come up with a strategy to test a range of values for the variable
you decide to change. You should run at least 4 tests.
c. Make a prediction about how you think your variable will
affect the system. Be specific in your prediction.
For example, let’s say you decide to explore how the initial size of
the sheep population affects the system. Your prediction would
state: “I think a low initial population size of sheep will
cause________ because ______. I think a high initial sheep
population size will cause ______ because _______.”
d. Run the tests. Record the results in a table. Run each variation at
least twice to see if the results are the similar.
To start the simulation with new values, move the appropriate
slider to the position you want. Next, press Setup, and then
press Go.
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Elaborate
16.Discuss the results with your partner. Then, on your own, make a claim about
how your team’s variable affected the 3 species in the food chain. Make sure
you tie your claim to specific evidence. Describe how the evidence leads to
your claim. Also make sure that you address whether or not the evidence
supports your initial prediction.
17.Contribute your results to a class discussion about the impact of different
variables. Use this discussion to answer the focus question, “How can a
variable in one population affect other organisms in a food chain?”
Reflect and Connect
Use the information you learned in the simulation to answer the following
questions. Write your answers in your science notebook.
1.Were there any changes to the simulation that made some species go extinct?
If so, describe what they were. You may use results from your own work or
that you learned during the class discussion.
2.You explored a simple model of a food chain. What do you think are some
of the limitations of this simple model?
In other words, what important factors may not be included
in the model?
3. Why are models an important part of scientific inquiry?
4.The teamwork skill that you are working on in this chapter is making sure
everyone understands.
a. Describe 1 or 2 specific things that you did that helped your partner
understand the simulation.
b. Describe 1 or 2 specific things you think you could do better to help
someone understand in the future.
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Evaluate
Menu Connections
Suppose you go down to the cafeteria for lunch. Today’s menu? Chicken
sandwich, salad, and chocolate cake. Yum! Just three menu items. But how many
living things are parts of your meal? When you examine this question, you will
see your connections to the web of life—and this is just one meal!
In this Evaluate activity, Menu Connections, you’ll show what you’ve learned
about ecosystems and energy. To show what you’ve learned, you will construct a
food web based on your lunch. You will analyze how energy gets transferred in the
food web. You’ll also make predictions about the impact of different changes to
the food web.
Materials
For each student
1 large piece of paper
1 set of different-colored pens or pencils, 5 colors
1 copy of Menu Connections Rubric handout
1 copy of What’s for Lunch? handout
sticky notes
Process and Procedure
1.Examine the Menu Connections Rubric handout. This helps you know how to
do your best on this activity. Ask your teacher about any parts of the rubric you
don’t understand.
2.On your own, list in your science notebook all the different organisms that you
think contributed to your “lunch.” The 3 menu items are
n a chicken sandwich with ketchup, pickles, and onions;
n a salad with lettuce, mushrooms, red peppers, carrots, olive oil,
and balsamic vinegar; and
n a piece of chocolate cake.
Many foods have ingredients that come from many plants,
animals, or fungi. Do the best you can to list as many organisms as
you can think of.
3.Compare your list of organisms to those of a partner. Revise your list based on
what you learn from your partner.
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Life Science Unit · Living Energy
Chapter 2 · Ecosystems and Energy
Evaluate
4.Get a copy of the What’s for Lunch? handout. Read the Main Requirements
for Each Food section and then the 2 tables. How many of the organisms are
the same as those on your list?
5.Create a table on a new page in your science notebook. The table should
have 5 columns. Label the columns “producer,” “herbivore,” “omnivore,”
“carnivore,” and “decomposer.” Leave plenty of rows underneath each column
heading. Title the table “organisms needed for lunch.”
6.Read the What’s for Lunch? handout again. As you read through the Main
Requirements for Each Food section, notice that some of the items are organisms. For example, lettuce is a plant. Add these organisms to your Organisms
Needed for Lunch table. Place each organism in the appropriate column.
Yeast are fungi that act as decomposers.
7.Many ingredients are products that come from organisms. For example, flour
comes from wheat plants. Read the Ingredients and Living Organisms table on
the What’s for Lunch? handout. As you read, place the organism that is the
source of each ingredient in your table. Again, make sure to put each organism
in the correct column.
8.Some of the organisms you listed in Step 7 are animals that have their own diet.
Include the organisms that are a part of these animals’ diets in your table, too.
9.Create a food web from the information you have in your Organisms Needed
for Lunch table. Use the following directions to help you.
a.Get a large piece of paper from your teacher. Fold it to create 5
equal-sized sections. Also get 5 different-colored pens or pencils.
Use a different color for each section.
b.In the bottom section, list all the names of the plants. Label this
section “producers.”
c.Write the names of all the herbivores (plant eaters) in the next
section, above the plants. Label this section “herbivores.”
d.Write all the names of the omnivores (animals that eat plants
and animals) in the next section, above the herbivores. Label this
section “omnivores.”
e.Write all the names of the carnivores (animals that eat only meat)
in the section above the omnivore row. Label this section “carnivores.”
f.Include the decomposers at the top of the food web. Label this
section “decomposers.”
g.Write “humans” in the correct row for someone eating this lunch.
h.Draw arrows between organisms to create a food web.
i.Place the Sun on your diagram and indicate how energy from the
Sun affects your personal food web.
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Chapter 2 · Ecosystems and Energy
Evaluate
10.Think of other organisms that might compete with you for your food. List at
least 4 other organisms that might eat some of the same foods as you. Add these
organisms to your food web.
For example, coyotes try to eat young cows (calves).
11.Make a simple energy transfer diagram in your science notebook. The diagram
should summarize one pathway of energy transfers from the Sun to you. Make
sure to show where thermal energy leaves the pathway.
12.Exchange your food web and your energy transfer diagram with a partner.
Follow Steps 12a–d as you review your partner’s work.
a. Provide at least 2 pieces of feedback to your partner on separate sticky
notes. Stick the notes on your partner’s work near the location where it
best applies.
You may want to add additional organisms to your partner’s food
web. You might also think about the following questions:
• Are the arrows on the food web pointing in the correct direction?
• Are the organisms in the correct row? For example, are all the
plants included in the producers’ row?
• Is thermal energy included in the energy transfer diagram?
b. Return your partner’s food web.
c. Examine the feedback you received from your partner. Carefully
consider each suggestion.
evise your design based on helpful feedback. Make any revisions
d. R
in a different color.
13.Corn can be used for food or to make fuel. Predict how 2 of the other organisms
in the food web could be affected if a lot of corn were used for fuel instead of
food. Write your prediction in your science notebook.
At least one of the other two organisms should not eat corn
directly. Recall how changes in grass influenced sheep and wolf
populations in the simulations.
14. In the Engage activity, you answered the question “Which do you think are
more important to human survival: plants or animals? Why do you think that?”
Revise your answer to this question after examining your lunch food web. Use
what you know about energy at different feeding levels.
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Chapter 2 · Ecosystems and Energy
Spanish Vocabulary
Spanish Vocabulary
analogy: analogía
arthropods: artrópodos
biosphere: biósfera
carnivores: carnívoros
community: comunidad
consumers: consumidores
decomposers: descomponedores
ecosystem: ecosistema
energy pyramid: pirámide de energía
food chain: cadena alimenticia
food web: red alimenticia
fungi: hongos
herbivores: herbívoros
mass: masa
model: demostrar (verb)/ modelo (noun)
producers: productores
species: especie
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