2. 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
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:2. 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 and in place during microscopic observation.
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 viewed with a microscope instead of the whole leaf because the leaf peel is thinner, allowing light to pass through. If the whole leaf were used, it would be too thick and opaque, preventing the light from shining through effectively. This method also enables the stomata and guard cells to be identified more easily.
Step 3
State the number of stomata visible on Figure 4.
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Answer
There are 3 stomata visible on Figure 4.
Step 4
Describe how stomata open.
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Answer
Stomata open as the guard cells take in water through osmosis. This increase in water causes the guard cells to become turgid, changing their shape and leading to the opening of the stomata.
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 stomata on the lower surface of the leaf helps to reduce water loss, as it minimizes direct exposure to sunlight and air currents. This positioning allows for gas exchange while maintaining moisture levels, which is crucial for plant survival.
