A student examined a thin slice cut through the blade of a leaf from a flowering plant and viewed it under a microscope to see how the leaf is built. The di...
Question 1 Report
A student examined a thin slice cut through the blade of a leaf from a flowering plant and viewed it under a microscope to see how the leaf is built. The diagram shows this cross-section through the leaf. Several tissue layers can be seen, from the protective covering on the outer surfaces to the packed cells in the middle of the leaf and the small openings on one surface through which gases move. Water that is drawn up from the roots reaches the leaf and travels through its cells before some of it is lost to the surrounding air. This loss of water from the plant is called transpiration, and the rate at which it happens depends on the structure of the leaf and on the conditions around the plant. The student used the diagram, together with knowledge of how water travels through a plant, to answer the following questions about the leaf and about the loss of water from it.
(a) Define the term transpiration. [2]
(b) Name the tissue that transports water up the stem to the leaf. [1]
(c) State two environmental conditions that would increase the rate of transpiration. [2]
Answer Details
(a) Transpiration is the loss of water vapour from the leaves (aerial parts) of a plant [1], by evaporation from the mesophyll cells and diffusion out through the stomata [1]. [2]
(b) Water is carried up the stem to the leaf in the xylem. [1]
(c) Any two conditions that increase the rate (1 mark each): higher temperature, increased air movement / wind, lower humidity, or higher light intensity (which opens the stomata wider). [2]
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