Grade 7 Science
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Module 5, Lesson 4
33
Lesson 4
Energy in the Ecosystem
"'Vocabulary:};
• photosynthesis
Learning Outcomes
• cellular
•
respiration
After completing this lesson you will be able to
indicators
q
describe photosynthesis
q
describe cellular respiration
q
explain how photosynthesis and cellular
respiration are part of the cycling of matter and
the transfer of energy in ecosystems
Sources of Energy for the Ecosystem
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All living things require food. Food, in turn, provides the energy
and matter for all life processes. In this lesson we will see how
the Sun is ultimately the source of energy for all ecosystems.
We will also follow the path that energy travels as it goes
through an ecosystem.
Green plants convert the Sun's energy into chemical energy.
This is the first step in the path that energy takes in an
ecosystem. Green plants make their own food by
photosynthesis.
Photosynthesis is the process by which water, carbon dioxide,
and light energy are transformed into sugar (stored energy).
For this process to take place, the chemical chlorophyll must be
present. Chlorophyll is found in green plants and algae. Almost
all of the other forms of life depend on green plants for their
own food needs. Whether organisms eat plants themselves or
they eat animals that eat the plants, somewhere along the
feeding chain, an organism eats a plant.
Grade 7 Science
Module 5, Lesson 4
34
Plants are also important because they
supply the environment with oxygen.
Oxygen is a byproduct of photosynthesis
and is vital for the survival of living
things. Oxygen is needed to release the
stored energy in food. Cellular
respiration is the process that releases this stored energy.
Sugars (stored energy) are combined with oxygen to release the
energy and give off carbon dioxide as a by-product.
Photosynthesis and cellular respiration are part of the cycling of
matter and the transfer of energy in ecosystems.
Photosynthesis Word Equation
Scientists use word equations to describe what is needed for a
chemical process to take place, and what is produced from it.
The following is the word equation for photosynthesis:
water + carbon + light
energy
dioxide
chlorophyll
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sugar + oxygen
Questions: Photosynthesis
Using the equation above and the description of photosynthesis
from earlier in this lesson, answer the following questions.
1. What are the inputs (things needed for the process to take
place)?
2. What are the outputs (things that result from the process)?
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Grade 7 Science
Module 5, Lesson 4
37
C
3. Where does the water and carbon dioxide come from?
4. What happens to the sugar and oxygen?
5. What is important about chlorophyll?
Cellular Respiration Word Equation
The process by which cells release the energy stored in sugars
(obtained from food) is called cellular respiration. The following
is the word equation for this energy releasing process:
sugar + oxygen
C
3m, carbon dioxide + water + energy
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Module 5, Lesson 4
Grade 7 Science
Questions: Cellular Respiration
1. What are the inputs (things needed for the process to take
place)?
2. What are the outputs (things that result from the .process)?
3. Where does the sugar come from?
4. Where does the oxygen come from?
5. What happens to the carbon dioxide, water, and energy?
O