How Do Food Chains Show Relationships In A Habitat?
All living things need energy to live. A food chain
shows one path of the flow of energy and nutrients
(or food) within an ecosystem or habitat. Effectively, a
food chain shows the relationships between predators
and prey.
The primary source of energy for all living things on
Earth is the sun. Plants absorb energy from the sun
which they convert to chemical energy through a
process called photosynthesis. They also take in
nutrients, which contain energy, from the soil and use
them to produce leaves, flowers and fruit. This is the
beginning of energy conversion. Plants are primary
producers (autotrophs) because they make their own
food. All the species in an ecosystem or habitat
depend on autotrophs.
Primary produce are consumed (eaten). All
consumers, because they cannot make their own food
and must depend on others for energy, are called
heterotrophs. There are different levels of consumers
and ways of classifying them. Consumers are most
commonly classified by the food they eat.
Primary consumers are herbivores (such as
grasshoppers and rabbits) and eat plants. They must
obtain all the energy they require from consuming
plants. Secondary consumers are carnivorous animals
(meat eaters) that eat primary consumers
(herbivores). A fox, for example, will consume a
rabbit. Omnivores eat both plants and animals and also fit into this group. Tertiary
consumers are carnivores that eat other carnivores. A bear, for example, will eat a fox. Some
scientists also include another group, call quaternary consumers, in the food chain. This
group consists of larger carnivorous animals which eat smaller carnivores. Examples of
quaternary consumers are the white shark and polar bear. The top predators, or consumers,
in a food chain usually have few or no natural enemies.
When an animal in a food chain dies, it may be eaten by detrivores (animals such as vultures,
crows, beetles or crabs) and then be broken down by decomposers such as dung beetles,
bacteria and fungi. Decomposers speed up the decaying process and release nutrients back
into the soil for plants to use. The process of energy transfer then continues.
The levels of a food chain, called trophic levels, tell the position an organism holds in the
food chain. The arrows in a food chain are drawn from food source to food consumer. The
amount of energy transferred along a food chain decreased with each level.
How Do Food Chains Show Relationships In A Habitat? - 2
Use the text on the previous page to complete the following.
1. What is the difference between a primary source of energy, a primary producer and a
primary consumer? Give one example of each from the text in your explanation.
2. What is the relationship between secondary, tertiary and quaternary consumers in a
food chain? Give an example of each.
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
3. Explain the difference between an autotroph and a heterotroph.
4. Which two words describe the final group of organisms in a food chain responsible for
speeding up the decaying process?
__________________________
_________________________
5. Classify the following organisms, which belong in marine habitats, according to their
position in the food chain. Use the words in the box.
Primary producer
primary consumer
secondary consumer
Tertiary consumer
quaternary consumer
a)
b)
c)
d)
e)
Whale
Phytoplankton (can photosynthesise)
Seal
Herring
Zooplankton (cannot photosynthesise)
f)
g)
h)
i)
j)
Water flea
Bass
Algae
Crayfish
Kingfisher (bird)
6. Suggest 2 ways organisms in a food chain could be classified other than
primary producers or primary, secondary, tertiary or quaternary
consumers.
Auto___________________ or _____________________
_______________________or______________________ or omnivore