The diagram shows the lower epidermis of a leaf from a shore plant collected at midday. Two guard cells surround opening Q. The plant grows where the soil i...
Question 1 Report
The diagram shows the lower epidermis of a leaf from a shore plant collected at midday. Two guard cells surround opening Q. The plant grows where the soil is salty, so it must reduce unnecessary water loss while still allowing carbon dioxide to enter leaf cells for photosynthesis. Scientists compared this leaf with a leaf from a water lily.
(a) Name opening Q. [1]
(b) Describe how guard cells cause Q to open. [3]
(c) Explain why closing Q on a hot day reduces water loss from the plant. [2]
(d) State two factors, other than temperature, that can affect the rate of transpiration. [2]
(e) Suggest why water-lily leaves usually have most stomata on their upper surface. [1]
Answer Details
(a) Opening Q is a stoma, or stomatal pore. [1]
(b) Guard cells take up solutes. Water then enters the guard cells by osmosis. The cells become turgid and curve apart, opening the pore. [3]
(c) When Q closes, less water vapour diffuses out through the stomata. Therefore transpiration and water loss decrease. [2]
(d) Two factors other than temperature are light intensity and humidity. [2] Wind speed and leaf surface area are also valid.
(e) Water-lily leaves usually have most stomata on the upper surface because the lower surface is in contact with water, while the upper surface is exposed to air for gas exchange. [1]
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