The diagram shows the lower surface of a leaf from a mangrove plant. The plant grows in salty mud, but its leaf cells still need carbon dioxide for photosyn...
Question 1 Report
The diagram shows the lower surface of a leaf from a mangrove plant. The plant grows in salty mud, but its leaf cells still need carbon dioxide for photosynthesis and oxygen for respiration. The labelled pores are open during the day.
(a) Name the pore in the leaf surface through which gases diffuse. [1]
(b) Describe the movement of carbon dioxide and oxygen between the air and this leaf during daylight. [3]
(c) Explain how guard cells control gas exchange through a stoma. [3]
(d) Explain why closing stomata during a very hot afternoon can benefit the mangrove plant, but can also reduce its rate of photosynthesis. [4]
Answer Details
(a) The pore is a stoma; plural: stomata. [1]
(b) In daylight, carbon dioxide diffuses from the air into the leaf. [1] Oxygen diffuses from the leaf to the air. [1] Both gases move through stomata down concentration gradients. [1]
(c) Guard cells take up water by osmosis and become turgid. [1] Their shape makes the stomatal pore open. [1] When they lose water, they become flaccid and the pore closes. [1]
(d) Closing stomata reduces water loss by transpiration. [1] This helps prevent dehydration and maintains cell turgor. [1] However, less carbon dioxide enters the leaf. [1] Carbon dioxide can then become a limiting factor, so photosynthesis decreases. [1]
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