A student compared the number of stomata on the upper and lower surfaces of a leaf - Edexcel - GCSE Biology Combined Science - Question 2 - 2018 - Paper 1
Question 2
A student compared the number of stomata on the upper and lower surfaces of a leaf. She completed a leaf peel as shown in Figure 3.
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Worked Solution & Example Answer:A student compared the number of stomata on the upper and lower surfaces of a leaf - Edexcel - GCSE Biology Combined Science - Question 2 - 2018 - Paper 1
Step 1
State why a coverslip is placed on top of the leaf peel.
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Answer
A coverslip is placed on top of the leaf peel to keep the leaf peel flat. This ensures that it remains in place during observation and protects the objective lens from damage.
Step 2
Explain why the leaf peel rather than the whole leaf was viewed with a microscope.
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Answer
The leaf peel was used instead of the whole leaf because the leaf peel is thin, allowing light to pass through, which is essential for viewing under a microscope. The whole leaf would be too thick and opaque, making it difficult to identify the stomata and cells.
Step 3
State the number of stomata visible on Figure 4.
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Answer
The number of stomata visible on Figure 4 is 3.
Step 4
Describe how stomata open.
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Answer
Stomata open through a process involving guard cells taking in water. When the guard cells absorb water, they become turgid, changing their shape and causing the stomatal pore to open, allowing gas exchange to occur.
Step 5
Explain why it is an advantage to the plant to have this distribution of stomata in the upper and lower surfaces of the leaf.
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Answer
Having no stomata on the upper surface reduces water loss during transpiration. Stomata located on the lower surface allow for gas exchange, which is essential for photosynthesis, while minimizing excess water loss by keeping the upper surface more protected.
