TOPIC: ENERGY FLOW IN LIVING ORGANISMS
SUBTOPIC: FOOD CHAINS
Plants get energy from the sun. The light energy allows the plant to split the water molecules
into oxygen and hydrogen. The hydrogen combines with carbon-dioxide to produce glucose.
The oxygen will be used in respiration and the excess will be released into the atmosphere.
The process of photosynthesis is carried out by green plants which are called producers or
autotrophs because they are capable of making their own food. Producers form the basis of all
food chains.
A food chain is a sequence by which energy in the form of food is passed on from one organism
to another.
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The rules that govern the drawing of food chains area as follows:
1. A food chain always begins with a producer.
2. Energy flows in one direction
3. The energy supplied from one level to another decreases
4. The more levels there are in a food chain the smaller the amount of available energy.
5. A food chain has a maximum of five organisms
6. Arrows are drawn from food source to food consumer. The arrow means ‘eaten by’ and
shows the direction in which energy flows.
CONSUMERS
Consumers are known as heterotrophs as they depend on other organisms for their food. There
are three main classes of heterotrophs:
a. Herbivores- organisms that consume plant matter only
b. Carnivores- organisms that consume flesh only
c. Omnivores- are organisms that consume both plant and animal matter
DECOMPOSERS - which include microscopic organisms bacteria and fungi, are organisms that
feed and dead and decaying matter and by so doing they assist in the recycling of nutrients.
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