Ecology is the study of living things and their surroundings. Energy enters most communities as light and leaves as heat.
The idea
A habitat is where an organism lives. A population is the members of one species there. A community is all the populations. An ecosystem is the community plus the non living surroundings. A food chain shows feeding links. It starts with a producer, a green plant that makes food by photosynthesis. A primary consumer eats the producer. A secondary consumer eats the primary consumer. Decomposers, such as many bacteria and fungi, break down dead material and return nutrients to the soil. Arrows in a food chain point the way the energy goes, from food to feeder, not the way the animal walks.
At each feeding step most of the energy is used by the organism or lost as heat. Only a small part is stored in the body and can be eaten by the next organism. That is why food chains are short, and why a pyramid of energy narrows as you go up. Removing the producer collapses the chain. Pollution, deforestation and overfishing remove organisms or poison the links. A question on conservation wants a reason tied to the chain or to people who depend on it, not a slogan.
What earns the marks
The arrow direction is a classic loss of a mark. Arrow from grass to goat, not from goat to grass. Producer, consumer and decomposer are roles, not particular species until the question names one. Do not say all the energy passes to the next level. Say that only a small part does. If you use a percentage, only use one the question gave you.
Practice questions
These are practice questions in the style of the paper, with a model answer and a mark scheme. They are not a promise of what your paper will ask.
1Question 1
4 marks
In a grassland: grass, lizard, hawk, grasshopper.
(a) Arrange them into a food chain. (2 marks)
(b) Name the producer and the secondary consumer. (2 marks)
Model answer
(a) Grass → grasshopper → lizard → hawk.
(b) The producer is the grass. The secondary consumer is the lizard.
Mark scheme
Grass first, then grasshopper, lizard and hawk, in that order1 mark
Arrows point from food to feeder1 mark
Producer: grass1 mark
Secondary consumer: lizard. The hawk is the tertiary consumer1 mark
2Question 2
2 marks
Explain why a food chain rarely has many steps. (2 marks)
Model answer
Most of the energy at each step is used by that organism or lost as heat. Too little remains to support another level after a few steps.
Mark scheme
Energy is lost, or used, at each step1 mark
Not enough remains to support many further levels1 mark
3Question 3
2 marks
State the role of decomposers in an ecosystem. (2 marks)
Model answer
They break down dead organisms and waste, and they release nutrients that plants can use again.
Mark scheme
Break down dead material or waste1 mark
Return nutrients to the soil or to the cycle1 mark
Practise Integrated Science with Anna
More questions on this topic are inside GLearn, marked as you answer, with the reason written out. The first ones need no account.
From the organism being eaten to the organism that eats it. The arrow shows the direction of energy flow. Grass → grasshopper is correct. Grasshopper → grass is not.
Why are food chains short?+
Energy is used or lost as heat at every step. Only a small part is stored in the body and passed on. After a few steps there is not enough energy to support another population. All WASSCE Integrated Science past questions