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Energy in an Ecosystem
One way to study the interactions of organisms
within an ecosystem is to follow the energy that
flows through it. Organisms differ in how they
obtain energy and are classified as autotrophs
or heterotrophs based on how they obtain it.
Autotrophs
All of the green plants and other organisms
that produce their own food in an ecosystem
are primary producers called autotrophs. An
autotroph
(AW tuh trohf) is an organism that
collects energy from sunlight or inorganic
substances to produce food.
Organisms that contain chlorophyll absorb light
energy during photosynthesis and use it to
convert the inorganic substances carbon
dioxide and water to organic molecules. In
places where sunlight is unavailable, some
bacteria use hydrogen sulfide and carbon
dioxide to make organic molecules to use as
food. Autotrophs, including plants and algae,
are the foundation of all ecosystems because
they make energy available for all other organ-
isms in an ecosystem.
Heterotrophs
A
heterotroph
(HE tuh roh trohf) is an organ-
ism that gets its energy requirements by
consuming other organisms. Therefore, hetero-
trophs also are called
consumers
. A heterotroph
that eats only plants, such as a cow, rabbit, or
grasshopper, is an
herbivore
(HUR buh vor).
Heterotrophs that prey on other heterotrophs,
such as wolves, lions, and lynxes, shown in
Figure 12
, are called
carnivores
(KAR nuh
vorz).
Figure 12
This wolf is a heterotroph that is about to
consume another heterotroph, a moose.
Identify
an additional classification for each of these
animals.
Disciplinary Core Ideas
Crosscutting Concepts
Science & Engineering Practices
3D THINKING
C
C
C
S
E
P
D
C
I
COLLECT EVIDENCE
Use your Science Journal to
record the evidence you collect as
you complete the readings and
activities in this lesson.
INVESTIGATE
GO ONLINE
to find these activities and more resources.
Applying Practices:
Ecological Pyramids
HS-LS2-4.
Use mathematical representations to support claims
for the cycling of
matter
and flow of energy among organisms in an ecosystem.
LESSON 2
FLOW OF ENERGY IN AN ECOSYSTEM
FOCUS QUESTION
How does energy flow through an ecosystem?
Lesson 2 • Flow of Energy in an Ecosystem
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