Grade 7 Science
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Module 5, Lesson 5
41
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Lesson 5
Energy Transfer in an Ecosystem
`
1ocabulary`#
• producers
• consumers
• primary
•
•
•
•
•
•
•
•
•
consumers
herbivores
secondary
consumers
tertiary consumers
carnivores
omnivores
scavengers
decomposers
food chain
ecological
pyramid
e
bioaccumulation
Learning Outcomes
After completing this lesson you will be able to
q
analyze food webs to show energy gained or lost
at various consumer levels
q
obtain information from ecological pyramids
q
describe the implications of the loss of producers
and consumers to the transfer of energy within
an ecosystem
Energy Transfer within a Food Chain
As you studied in the previous lesson, the original source of the
energy that fuels living organisms on Earth is the Sun.
Through the process of photosynthesis, this energy is
transformed by green plants into chemical energy and stored as
sugar, starch, or oil in the plant. Green plants and green algae
are the only types of organisms that can make their own food.
They are known as producers for this reason.
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Organisms that cannot make their own food are called
consumers. These organisms must obtain food energy by
eating plants or other organisms. The organisms that eat plants
are consideredoprimary consumers and are often called
7herbivores. Those organisms that eat primary consumers are
called secondary consumers and those that eat secondary
ones are called9tertiary consumers. Those secondary and
tertiary consumers that only eat meat are known as
t°carnivores. Organisms that eat both plants and animals are
(tomnivores. Bears are known omnivores.
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O
W
Grade 7 Science
Module 5, Lesson 5
42
The job of recycling nutrients in the environment is done by
scavengers and decomposers. Scavengers are animals that
feed on dead organisms. Some examples of scavengers are
vultures, hyenas, and ravens.Decomposers are organisms like
bacteria and maggots that break down wastes and dead
organisms, and return nutrients back to the soil.
Living things depend upon each other for food. Every living thing
is a link in a food chain. A^food chain shows the order in which
living things feed upon other living things.
Look at Figure A. It shows a food chain. The arrows in the food
chain show the direction that food moves along the chain.
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or nc1
Figure A
Iry
Not all organisms eat the same kinds of food. Therefore, there are
bmany different food chains. But, all food chains begin with
PRODUCERS.
WHY?
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Producers are the only organisms that can make their own food,
using energy from the Sun.
Why is the Sun the source of energy in an ecosystem?
lwd /fie
((av l
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a^
dice
(continued)
From Science Workshop Series: Biology: Dynamic Processes by Seymour
Rosen. ©1992 by Globe Fearon, an imprint of Pearson Learning, a division
of Pearson Education Inc. Used by permission.
Grade 7 Science
Module 5, Lesson 5
43
Six food chains are shown below. One link has been left out of
each chain. Identify the organism that is missing. Write your
answers in the proper spaces below. Some blank spaces have
more than one answer.
a
Word bank:
grain
wolf
mouse
leaf
bird
antelope
bobcat/coyote
Grade 7 Science
Module 5, Lesson 5
44
You have learned that food chains show food relationships.
However, in nature, many food chains combine and overlap. They
form a food web. A food web is a more complete way of showing
food relationships. Affood web shows how a number of food chains
are related.
Look at the food web in Figure C. Then answer the questions.
1. What is the diagram
shown called?
C
)& 4
U
2. What does the diagram
shoe
e
3.
spa" 4^
What two organisms does
rabbit eat?
7f?/4d4t
a
4. What organisms do wolves
Figure C
5. Which organism is the producer?
r
MAKE YOUR OWN FOOD CHAIN
In the space provided, draw one of the food chains shown in the
diagram above.
(continued)