O/L Science 2018–2019 — past paper questions and answers
3 questions with worked solutions from 2018–2019: 16 marks in all, from Paper II. Aligned with the NIE syllabus
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Question 3 works from a leaf seen in cross-section under a microscope. It asks you to name the layer holding the most chloroplasts and say why, to state what the stomata do and describe how they open and close, and to explain why a variegated leaf makes starch only in its green parts.
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(i) The palisade mesophyll layer contains the most chloroplasts — it is near the upper surface and receives the most light for photosynthesis. (ii) Stomata allow gas exchange (CO₂ in, O₂ out) and transpiration. Guard cells swell (fill with water) in light → pore opens; lose water in dark/dry → pore closes. (iii) White regions lack chlorophyll (no chloroplasts) → photosynthesis cannot occur → no starch produced. Only green regions with chloroplasts carry out photosynthesis.Theory notes on this topic: Plant Structure and Transport in Plants →
Source: Department of Examinations, Sri Lanka — G.C.E. O/L Science 2018, Paper II, Question 3 · https://doenets.lk/pastpapers -
Question 6 holds a ball of stated mass at rest at a stated height, with g supplied. It asks you to calculate the ball's gravitational potential energy, then its kinetic energy just before it lands with air resistance ignored, and to name the energy transformation that happens as it falls.
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(i) GPE = mgh = 2 × 10 × 5 = 100 J (ii) By conservation of energy, KE = GPE = 100 J (no energy lost to friction). (iii) Gravitational potential energy → Kinetic energy.Theory notes on this topic: Forms and Transformations of Energy →
Source: Department of Examinations, Sri Lanka — G.C.E. O/L Science 2019, Paper II, Question 6 · https://doenets.lk/pastpapers -
Question 5 gives an electric heater of stated power warming a fixed mass of water through a stated temperature rise, with the specific heat capacity supplied. It asks you to calculate the thermal energy the water absorbs, then the time the heater takes at full efficiency, and to explain why a metal spoon in hot tea becomes hotter than a wooden one.
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(i) Q = mcΔT = 2 × 4200 × (70 − 20) = 2 × 4200 × 50 = 420 000 J (ii) P = Q / t → t = Q / P = 420 000 / 1 500 = 280 s (iii) Metal is a GOOD conductor of heat; free electrons transfer thermal energy quickly from the hot tea to the hand. Wood is a poor conductor (insulator); it does not transfer heat quickly, so it feels cooler.Theory notes on this topic: Heat, Temperature and Heat Transfer →
Source: Department of Examinations, Sri Lanka — G.C.E. O/L Science 2019, Paper II, Question 5 · https://doenets.lk/pastpapers
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Each question is cited to the past paper it comes from. The worked solutions are Idasara Academy's own work.