Biology - HOT Science Lab

Student
Designing Food Chains and Food Webs
NGSSS:
SC.912.L.17.9 Use a food web to identify and distinguish producers, consumers, and
decomposers. Explain the pathway of energy transfer through trophic levels and the reduction of
available energy at successive trophic levels. (AA)
Background: (Source: www.epa.gov)
All organisms in an ecosystem need energy to survive. This energy is obtained through food.
Producers obtain energy by making their own food whereas consumers must feed on other
organisms for energy. This dependence on other organisms for food leads to feeding
relationships that interconnect all living things in an ecosystem. A food chain illustrates the
simplest kind of feeding relationship. For example, in a forest ecosystem, a grasshopper feeds
on plants. The grasshopper is consumed by a spider and the spider is eaten by a bird. Finally,
that bird is hunted by a hawk. A food chain clearly shows this pathway of food consumption.
You could probably think of another food chain for a forest ecosystem. In fact, many different
food chains exist in ecosystems. Although there are many different kinds of food chains, each
food chain follows the same general pattern. A link in a food chain is called a trophic, or feeding
level. The trophic levels are numbered as the first, second, third, and fourth levels, starting with
the producers.
Each of the trophic levels is occupied by a certain kind of organism. Producers are always in the
first trophic level since they do not feed on another organism. Consumers occupy the rest of the
trophic levels. The second trophic level is the first consumer in the food chain and is called a
primary consumer. Primary consumers eat plants and are therefore herbivores or omnivores.
The next consumer in the food chain is the secondary consumer. The secondary consumer is in
the third trophic level. Since the secondary consumer feeds on another animal, it is a carnivore
or an omnivore. Similarly, the tertiary consumer occupies the fourth trophic level, and is a
carnivore. The last link in a food chain is also referred to as the top carnivore since it is at the
top of the food chain and is not hunted by other animals.
Biology HSL Page 45
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