QUESTION 5
- (i) What are sense organs? [3 marks]
(ii) Name three sense organs that respond to the stimulus of chemicals. [3 marks]
- List three animals each that exhibit the following courtship behaviours.
- territoriality
- pairing [6 marks]
- (i) State one similarity between the eggs of toads and the eggs of birds. [1 mark]
(ii) State three differences between the eggs of toads and the eggs of birds. [3 marks]
- Complete the table below by listing four organisms involved in the nitrogen cycle and state one role each of the organisms.
Four organisms involved in the nitrogen cycle |
One role of each organism |
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[8 marks]
- Complete the table below by naming two types of heterotrophic modes of nutrition in animals and give two examples each of the organisms that carry out the modes of nutrition.
Two modes of heterotrophic nutrition |
Two examples of organisms that carry out mode of nutrition |
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[6 marks]
This question was attempted by many candidates.
Most candidates were able to define sense organs with examples.
Poor spellings made some candidates to lose marks for example spelling tongue as tounge, yoke instead of yolk etc.
In question 5(b)(i), many candidates could not give correct examples of animals that exhibit territoriality some instead were mentioning animals like Zebra, Elephant, Antelope etc.
Many candidates gave wrong responses in question 5(c)(iii). They wrote it is hydrated/it is not hydrated; absence of amniotic fluid/presence of amniotic fluid; cannot survive on land/can survive on land etc.
The organisms involved in nitrogen fixation and their roles were wrongly answered by many candidates.
Many candidates gave correct answers in question 5(e) Few however could not give correct examples for the mode of nutrition mentioned.
The expected answers are as follows:
(a) (i) Sense organs
Organs with sensory receptors; that detect changes from the environment; and relay
the impulses to the nervous system; for interpretation and appropriate response sent
to the effector organ.
(ii) Sense organs that respond to the stimulus of chemicals
- Tongue;
- Nose;
- Skin;
- Eye.
(b) (i) Animals that exhibit territoriality
- Agama lizard/lizard;
- Leopard/tiger;
- Jaguar;
- Lion;
- Monkey;
- Chimpanzee/baboon;
- Dog;
- Cat;
- Male Tilapia.
(ii) Animals that exhibit pairing
- Termite;
- Human;
- Gibbon;
- Domestic fowl/duck/pigeon;
- Fish;
- Spider;
- Monkey;
- Toad.
(c) (i) Similarities between eggs of toads and eggs of birds
Both have yolk; embryo; vitelline membrane.
(ii) Differences between eggs of toads and eggs of birds
Eggs of toads |
Eggs of birds |
Surrounded by jelly coat |
surrounded by calcareous shell; |
Relatively smaller |
relatively larger; |
Shell membrane absent |
shell membrane present; |
Presence of black part |
no black part; |
Eggs are laid in chains |
eggs are laid in single piece; |
Many/numerous eggs |
one egg at a time; |
Transparent |
opaque; |
Airspace absent |
airspace present; |
Yolk not suspended by chalaza |
Yolk suspended by chalaza. |
(d) Organisms involved in Nitrogen Cycle
Organisms involved in the nitrogen cycle |
One role of organism |
Animals |
Excrete nitrogenous compounds/ |
Plants |
Absorbs nitrate from soil/ |
Putrefying bacteria |
Break down dead plants/animals; |
Azotobacter |
Converts atmospheric nitrogen to nitrate; |
Rhizobium |
Converts atmospheric nitrogen to nitrates; |
Nitrobacter |
Converts nitrite to nitrates; |
Nitrosomonas |
Converts ammonium compound to nitrite; |
Pseudomonas |
Converts amino compound to ammonium compounds. |
(e) Types of heterotrophic nutrition
Two modes of heterotrophic Nutrition |
Two examples of organisms that carry out mode of |
Holozoic |
Human; domestic fowl; dog; cat; goat; sheep; cow; |
Parasitic |
Lice; tick; tapeworm; liver fluke; Guinea worm; hookworm; |
Saprophytic |
Fungi; mushroom; soil bacteria; yeast; |