Plant Biology

Practice past-paper questions

Practise O/L exam questions on Plant Biology with worked solutions

1. 2018 · Paper II · 5 marks
   A cross-section of a leaf is examined under a microscope. (i) Name the layer of the leaf that contains the most chloroplasts and explain why. (ii) State the function of stomata and describe how they open and close. (iii) Explain why variegated leaves (part green, part white) only produce starch in the green regions.
   Show worked solution

   (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.
   Source: NIE O/L Science 2018 Paper II Q3

Get this auto-marked

Related Topics

In the Syllabus