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39 Food Webs
BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN
Grade 3—Quarter 4
Activity 39
SC.B.1.2.1
The student knows how to trace the flow of energy in a system (e.g., as in an ecosystem).
SC.B.2.2.1
The student knows that some source of energy is needed for organisms to stay alive and
grow.
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The student knows how all animals depend on plants.
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The student knows ways that plants, animals, and protists interact.
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The student knows that living things compete in a climatic region with other living things
and that structural adaptations make them fit for an environment.
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The student knows that to work collaboratively, all team members should be free to reach,
explain, and justify their own individual conclusions.
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SC.H.1.2.5
The student knows that a model of something is different from the real thing but can be
used to learn something about the real thing.
ACTIVITY ASSESSMENT OPPORTUNITIES
The following suggestions are intended to help identify major concepts covered in the activity
that may need extra reinforcement. The goal is to provide opportunities to assess student
progress without creating the need for a separate, formal assessment session (or activity) for
each of the 40 hands-on activities at this grade level.
1. Ask, How does food energy flow in a food chain? (The food energy flows in one direction,
from a producer to a consumer that eats producers to a consumer that eats other
consumers.) How does food energy flow in a food web? (Food energy still flows from
producer to different levels of consumers, but it flows in many different directions.)
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2. Use the Activity Sheet(s) to assess student understanding of the major concepts in the
activity.
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activity 39 Food Webs
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In addition to the above assessment suggestions, the questions in bold and tasks that
students perform throughout the activity provide opportunities to identify areas that may
require additional review before proceeding further with the activity.
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39 Food Webs
OBJECTIVES
A vast food web connects all life in a
community. The students create food webs
that include the plants and animals they
have discussed as well as other common
animals.
The students
create diagrams of food webs on paper
compare food chains to food webs
infer why real food webs are so complex
PREPARATION
1
Make a copy of Activity Sheet 39 for each
team of two.
2
Copy a set of Food Web cards for each
team of two, using the heaviest stock
paper your copy machine will accept.
3
Squirt some glue onto a piece of scrap
paper for each team of two.
BACKGROUND INFORMATION
SCHEDULE
About 40 minutes
VOCABULARY
food web
Every living thing, whether plant or animal,
must have food to live. Plants use the energy
in sunlight to manufacture their own food
from carbon dioxide and water, but animals
must eat plants or other animals to survive.
The simple progressions studied in these
activities, such as grass
cricket
mouse
owl, are called food chains. In
most ecosystems, however, the arrangements
are not this simple, and are better illustrated
as food webs that show many organisms and
interconnected food chains.
MATERIALS
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1
Activity Sheet 39
1 set
Food Web cards
1 piece paper, white,
11 in. × 17 in.*
1 pair scissors*
mouse
glue
markers or crayons*
paper, scrap*
Delta Science Reader Food
Chains and Webs
*provided by the teacher
fox
cricket
seeds
grass
For the class
1 btl
anole
owl
For each team of two
Figure 39-1. A food web.
The simple food web shown in Figure 39-1
illustrates the greater complexity of a food
web as compared to a food chain. In this web,
there are two producers (grass and seeds),
three primary consumers (cricket, mouse, and
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fox), four secondary consumers (mouse, fox,
anole, and owl), and two tertiary consumers
(fox and owl). Nearly all the consumers depend
on more than one type of prey for food.
1
Write grass
mouse
owl on the
board, and ask, What do we call this
sequence?
Food Webs
leaves
fruit
seeds
cricket
fox
flowers
butterfly
robin
mouse
anole
earthworm
owl
Additional Information
This is a food chain.
grass
Add cricket and anole, as shown in Figure 39-2.
mouse
cricket
Ask, How should we connect these two
additional animals to this food chain?
Remind students that sometimes owls eat
anoles, and mice eat crickets, and ask, How
can we add arrows to show this?
Ask, How is this diagram different from a
simple food chain?
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activity 39 Food Webs
owl
anole
Figure 39-2. Building a simple food web.
The grass should have an arrow pointing to
the cricket and the cricket should have an
arrow pointing to the anole.
Students should suggest adding an arrow
pointing from the anole to the owl, and an
arrow pointing from the cricket to the mouse,
as shown in Figure 39-3.
This is a more complex arrangement.
Consumers eat more than one type of prey,
and prey are eaten by more than one type of
consumer.
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Guiding the Activity
Activity Sheet 39
Guiding the Activity
Write food web on the board. Explain that in
most places, plants and animals are
connected in more complicated ways—ways
that resemble webs more than chains. This
complex arrangement of organisms and food
chains is called a food web (see Figure 39-3).
2
grass
mouse
owl
cricket
anole
Figure 39-3. Building a simple food web.
Distribute a copy of Activity Sheet 39, an
11-in. × 17-in. piece of paper, scissors,
markers, a scrap of paper with glue, and a set
of Food Web cards to each team of two.
Instruct students to cut the circles out of
Activity Sheet 39 and glue them randomly
onto the large piece of paper. They also
should cut apart the Food Web cards and
stack them.
3
Additional Information
The students should use the information on
the Food Web cards to draw arrows showing
all the connections between the plants and
animals on their piece of paper (see Figure
39-4). Demonstrate this by having all the
teams read the fox card along with you, and
draw an arrow for each of the connections
mentioned.
Tell students to spread the circles out on the
paper so that there is a lot of room between
them.
There should be arrows pointing to the fox
from the fruit, robin, mouse, cricket, butterfly,
seeds, anole, and leaves.
Allow the students time to go through the
Food Web cards and complete their charts.
fruit
owl
earthworm
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mouse
robin
seeds
fox
butterfly
leaves
cricket
flowers
anole
Figure 39-4. Initial connections in the students’
food web.
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Guiding the Activity
5
Ask, Does your chart look more like a food
chain or a food web?
The chart looks like a food web.
Tell students that most relationships between
living things are more like food webs than
food chains.
Many food webs are so complex that it is
difficult to diagram them accurately.
Conclude by asking, Do animals eat only one
kind of prey? Are they eaten by only one
kind of predator? Why do you think that food
webs, rather than chains, exist in nature?
From their diagrams, students should see
that most animals eat a variety of plants or
other animals for food. Lead them to realize
that, in nature, animals encounter a number
of other organisms daily and that it would be
to their advantage to be able to draw
nourishment from a variety of these
organisms. If they depended exclusively on
one prey item, as the food-chain arrangement
implies, they could starve to death if that
prey item were suddenly to disappear.
As appropriate, read or review pages 4–9 of
the Delta Science Reader Food Chains and
Webs.
REINFORCEMENT
Have students create food webs with
common animals from your region. Be sure
that they include plants, several plant-eating
animals, and at least one predator. Challenge
them to include humans in their food web.
Assessment Opportunity
This Reinforcement also may be used as
an ongoing assessment of students’
understanding of science concepts
and skills.
SCIENCE JOURNALS
Have students place their completed
activity sheets in their science journals.
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activity 39 Food Webs
CLEANUP
Display the food web diagrams in the
classroom. Students may want to save the
Food Web cards for additional activities as
described in Connections. Return the bottle
of glue to the kit.
SCIENCE AT HOME
Have students look in their refrigerators
and cupboards to research the food webs
of which they are part. They may want to
draw a diagram of these and bring them to
class to discuss.
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4
Additional Information
Connections
Science Extension
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Explain that when a plant uses the energy
in sunlight to make its own food, most of
that energy is used for the plant’s life
processes. Only about 10% of the energy
that a plant receives from sunlight is
stored in the plant. When a mouse eats the
plant, it uses most of the food energy it
takes in for its own life processes and
stores only about 10% in its body. When an
owl eats the mouse, the owl gets only
about 10% of the food energy that the
mouse took in. Draw a large pyramid on
the board, and divide it into three sections.
Beginning at the bottom, label the sections
grass, mice, and owl. Tell students that the
pyramid shows what happens as food
energy passes from producers to different
levels of consumers in a food chain. To
show students how quickly energy is “lost”
in a food chain, draw a second pyramid the
same size as before but with an additional
section labeled snakes between the mice
and the owl. The sections for the grass and
mice should be kept the same size as they
were in the first pyramid. Now, draw a third
pyramid with yet another section labeled
crickets between the grass and the mice. In
this third pyramid, keep the section for
grass the same size as before, but reduce
the sizes of the mice, snake, and owl
sections to accommodate the crickets
section. Explain that because such a small
amount of the food energy stored in plants
ever reaches the top consumer in a food
chain, most chains contain no more than
four levels of consumers.
Science and Math
Divide the class into teams of three. Give one
student in each team a sheet of graph paper,
and tell the student that he or she represents a
plant. Have the student outline a 10 × 10 block
of squares on the graph paper and cut it out.
Then tell the student to cut off a row of 10
squares from the block and pass it to a second
student, who represents a mouse. Tell the
“mouse” to cut off one square from the row
and pass it to the third student, who represents
an owl. Students can see that only a small
portion of the original food energy stored in the
plant reaches the owl. You may want to have
students repeat the activity to illustrate a fourlevel chain that includes a snake and a fivelevel chain that includes a cricket. (Students
will need to tape sheets of graph paper
together in order to start with a block large
enough for the owl to receive one square.)
Science, Technology, and Society
Explain that just as food energy passes up a
food chain, so do many poisonous
substances. However, because these poisons
are not used for life processes, all of the
poison that an animal takes in is passed on to
the next-level consumer. If a farmer’s field is
sprayed with a poison to kill insect pests,
mice that eat the dead and dying insects will
take in the poison, too. An owl, hawk, or fox
that eats the mice will take in the poison. In
this way, poisons work their way up a food
chain and harm or kill animals that were not
meant to be poisoned. Ask students to find
out more about poisons in food chains.
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activity 39 Food Webs