Question 1

The diagram below shows two cells X and Y. Cell X has a cell wall, large central vacuole, chloroplasts and a nucleus. Cell Y has a nucleus, cell membrane and mitochondria only.
(i) Identify cell X and cell Y, giving ONE reason for each.
(ii) State the function of the mitochondrion.
(iii) Name the process that takes place in the chloroplast.

Accepted Answer

(i) X is a PLANT cell — because it has a cell wall, chloroplasts and a large central vacuole (features absent in animal cells). Y is an ANIMAL cell — because it lacks a cell wall and chloroplasts.
(ii) Mitochondria are the site of aerobic respiration — they release energy (ATP) from glucose for cell activities.
(iii) Photosynthesis occurs in the chloroplast.

Question 2

The diagram shows a food chain in a garden: Cabbage → Caterpillar → Frog → Snake → Hawk.
(i) Identify the producer and the apex predator.
(ii) What would happen to the frog population if all the snakes were removed? Explain.
(iii) Define the term 'ecosystem'.

Accepted Answer

(i) Producer: Cabbage. Apex predator: Hawk.
(ii) The frog population would INCREASE because the snake (frog's predator) is removed; fewer frogs are eaten. Over time caterpillar numbers would decrease because more frogs eat them.
(iii) An ecosystem is a community of living organisms interacting with each other and with their non-living environment in a particular area.

Question 3

A simple transistor switch circuit is used to turn a LED on and off.
(i) Draw the symbol of an NPN transistor and label its three terminals.
(ii) State the condition needed at the base terminal to allow current to flow from collector to emitter.
(iii) Name ONE practical application of a transistor switch circuit.

Accepted Answer

(i) NPN transistor has three terminals: Base (B), Collector (C), Emitter (E). The arrow on the emitter points outward.
(ii) A small forward-bias voltage (≥ 0.7 V for silicon) must be applied at the Base terminal to turn the transistor ON and allow current from Collector to Emitter.
(iii) Automatic street lighting (light-dependent switch), alarm systems, or motor speed control.

Question 4

The table below shows the population of organisms in a freshwater pond over three years.
Year 1: Algae 10 000 / Small fish 500 / Large fish 50
Year 3: Algae 5 000 / Small fish 400 / Large fish 30
(i) Suggest ONE reason for the decline in algae population.
(ii) Explain the relationship between small fish and large fish populations shown in the data.
(iii) Define biodiversity and state ONE reason why it is important.

Accepted Answer

(i) Reduced light penetration (eutrophication / pollution reducing photosynthesis); or increased grazing by small fish (accept any valid environmental cause).
(ii) As large fish decrease (fewer predators), small fish numbers could initially increase — but the data shows both decline together, suggesting a common stressor (e.g. habitat loss / pollution) or time lag in predator-prey dynamics.
(iii) Biodiversity = the variety of living organisms in an ecosystem. It is important because it maintains ecosystem stability and provides food, medicines, and ecosystem services.

Science 2020