O/L Science 2020 — past paper questions and answers

1. #1 · Paper II · 5 marks
   Question 2 describes two cells by the structures each one contains. It asks you to identify both cells with one reason for each, to state the function of the mitochondrion, and to name the process that takes place in the chloroplast.
   Show worked solution

   (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.

   Theory notes on this topic: Plant and Animal Cells →

   Source: Department of Examinations, Sri Lanka — G.C.E. O/L Science 2020, Paper II, Question 2 · https://doenets.lk/pastpapers
2. #2 · Paper II · 5 marks
   Question 10 shows a five-link garden food chain as a diagram. It asks you to identify the producer and the apex predator, to say what would happen to one population if a predator above it were removed and explain why, and to define the term ecosystem.
   Show worked solution

   (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.

   Theory notes on this topic: Pollution, Climate Change and Conservation →

   Source: Department of Examinations, Sri Lanka — G.C.E. O/L Science 2020, Paper II, Question 10 · https://doenets.lk/pastpapers
3. #3 · Paper II · 5 marks
   Question 12 sets a simple transistor switch circuit driving an LED. It asks you to draw the NPN transistor symbol with its three terminals labelled, to state the condition needed at the base for current to flow from collector to emitter, and to name one practical application of such a switch.
   Show worked solution

   (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.

   Theory notes on this topic: Diodes, Transistors and Simple Circuits →

   Source: Department of Examinations, Sri Lanka — G.C.E. O/L Science 2020, Paper II, Question 12 · https://doenets.lk/pastpapers
4. #4 · Paper II · 6 marks
   Question 11 supplies a table of three organism populations in a freshwater pond across three years. It asks you to suggest one reason for the fall in the producer population, to explain the relationship the data shows between the two consumer populations, and to define biodiversity with one reason it matters.
   Show worked solution

   (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.

   Theory notes on this topic: Ecosystems, Food Chains and Biodiversity →

   Source: Department of Examinations, Sri Lanka — G.C.E. O/L Science 2020, Paper II, Question 11 · https://doenets.lk/pastpapers

Free Quiz Get this auto-marked

Each question is cited to the past paper it comes from. The worked solutions are Idasara Academy's own work.

← All past papers for this subject