Energy Flow in Ecosystems
An organism’s energy role is determined by how it obtains
energy and how it interacts with the other living things in its
ecosystem. An organism’s energy role in an ecosystem may be
that of a producer, consumer, or decomposer.
Plants, algae or phytoplankton, and some microorganisms
can carry out photosynthesis. In this process, the organism uses
the sun’s energy to turn water and carbon dioxide into glucose.
An organism that-can make its own food is a producer or an autotroph.
Producers are the source of all the food in an ecosystem.
Other organisms cannot make their own food. They depend on producers for food and
energy. An organism that obtains energy, by feeding on other organisms is a
consumer or heterotroph. They can be primary, secondary, tertiary, and
quaternary consumers.
Consumers are classified by what they eat.
Consumers that eat only plants are called
quaternary consumer
tertiary consumer
secondary consumer
Consumers that eat only other animals are
called carnivores. A consumer that eats both
plants and animals is called an omnivore.
(omni=all + vore= one that eats)
A scavenger is a carnivore that feeds
primary consumer
on the bodies of dead organisms. An
organism may play more than one role in an
What do you notice about the about of calories as you
move from one trophic level to the next?
Organisms that break down wastes and dead organisms and return the raw materials
to the environment are consumers called decomposers. As decomposers obtain energy
for their own needs, they return simple molecules to the environment to be used again
by other organisms like producers to help them grow. Examples of decomposers are
worms, bacteria, and fungi.
The flow of energy through an ecosystem
can be shown in diagrams called food chains
and food webs. A food chain is a series of
events in which one organism eats another and
obtains energy.
The first organism in a food chain is always a
Food chain
The arrow shows the direction of the energy. For
example, energy goes from the sun to the grass;
from the grass to the grasshopper, etc.
producer. The second organism, called a primary
consumer, eats the producer.
The next consumer, called a secondary consumer, eats the
primary consumer. The next levels would be tertiary and even
quaternary consumers. A food chain shows just one possible
path of energy through an ecosystem.
Terrestrial food web
Most producers and
consumers are part of
many food chains. A
more realistic way to
show the flow of energy through an ecosystem
is a food web. A food web consists of the
many overlapping food chains in an
ecosystem. Food webs may be aquatic
(marine) or terrestrial (land).
When an organism makes its own food or eats
other organisms, it obtains energy. The organism uses most of this energy for its own life
processes. Only some of the energy will be available to the next organism in the food
web. A diagram called an energy pyramid (see page 1) shows the amount of energy
that moves from one feeding level to another in a food web. The most energy is
available at the producer level. At each level in the pyramid, there is less available
energy than at the level below. In general, only about 10% of the energy at one level of a
food web is transferred to the next higher level. For this reason, most food webs have
only three or four feeding levels, with few organisms at the highest level in a food web.
Energy Flow in Ecosystems
1. What is an energy role? _____________________________________________________________
2. Name the three energy roles in an ecosystem .
1._________________________ 2. __________________________ 3. _____________________
3. Name some producers._____________________________________________________
4. Who are the source of all the food in an ecosystem? _________________ and
What is its other name? ____________________________
5. What is a consumer? ______________________________________________________________
and what is its other name? _________________________________
6. Name the levels of consumers that are in a food pyramid.
7. Match the following;
a. only eats plants
b. only eats other animals
c. eats both plants and animals
8. What is a carnivore that feeds on the bodies of dead organisms? ________________________
9. What is the niche of a decomposer? _______________________________________________
10.Give examples of decomposers? _________________________________________________
11. How can the flow of energy be represented? _____________________ and ________________________
12. How is a food chain different from a food web? ___________________________________________
13. What is the first level in either a food chain or a food web? _________________________________
2500 kcal
1000 kcal
14. Which organism in the food web is sometimes a primary consumer and sometimes a secondary
consumer? ______________ Explain your answer._________________________________________
15.. Choose one food chain in the web above. Name all the organisms in that chain. Start with the
producer and end with the top-level consumer ___________________________________________
16. a. Draw on the energy pyramid the food chain you chose above.
Write the names of the organisms in the trophic level on the pyramid
b. Label the pyramid Include these words:
primary, secondary , tertiary consumers
the energy available at each level.
17. What is a terrestrial food web? ___________________________________________________
18. What is another name for an aquatic food web? _________________
19. How much energy is lost from one trophic level to the next? ______________________
Period______ Date_________
Food Webs at Hydrothermal Vents
Deep below the ocean’s surface are strange ecosystems called hydrothermal vents. Here, heated water
rises up through cracks in the ocean floor. The water contains minerals from Earth’s interior. No sunlight
ever reaches these vents. No plants or algae live there. The table below lists the organisms found at
hydrothermal vents.
Use the information in the table to respond to the following
1. Which organisms are the producers at hydrothermal vents?
2. Which organisms are primary consumers?
3. What type of consumer are the crabs?
4. In the space below, draw the food web (use words) at a hydrothermal vent.
Label each organism to identify its energy role (producer or consumer) in the ecosystem.

Energy Flow in Ecosystems