The loss of water vapour in transpiration, exchange of carbon-dioxide to oxygen in the leaf occurs through pores called stomata. Normally stomata are open in the day time and close during the night. The immediate cause of opening and closing of the stomata is a change in the turgidity of the guard cells. The inner wall of each guard cell towards the pore or stomatal aperture is thick and elastic. When turgidity increases within the two guard cells flanking each stomatal aperture or pore, the thin outer walls bulge out and force the inner walls into a crescent shape.

Match each of the following terms with its description. For some of the terms, there may be more than one description that matches them. Lignin, root hair, potometer, stoma, transpiration, xylem vessel. (a) A long tube made of empty cells joined end to end (b) Hard, strong tubes that help to support a plant (c) A strong, hard substance that makes up the walls of xylem vessels (d) An extension from a cell near the tip of a root, which absorbs water from the soil (e) The loss of water vapour from the leaves of a plant (f) A small gap between the cells of the epidermis of a plant (g) A piece of apparatus used for measuring the rate at which a plant shoot takes up water

(a) A long tube made of empty cells joined end to end:- Xylem vessel A xylem vessel is like a long drainpipe. It is made of many hollow, dead cells, joined end to end. The end walls of the cells have disappeared so a long open tube is formed. (b) Hard, strong tubes that help to support a plant:- lignin Lignin is so strong that it would certainly be possible for a tree to grow taller and support a plant to hold the tree up. (c) A strong, hard substance that makes up the walls of xylem vessels:- lignin Xylem vessels have walls made of a very strong substance is called lignin. It has two purposes like to hold the tree up and provide a pathway for water to move from the roots to the topmost leaves. The vessels have no cytoplasm (d) An extension from a cell near the tip of a root, which absorbs water from the soil:- root hair The root hairs are a little way up from the root tip. The functions of root hairs is to absorb water and minerals from the soil. Water moves into a root hair by osmosis. (e) The loss of water vapour from the leaves of a plant:- transpiration Transpiration is the evaporative loss of water by plants. It occurs mainly through the stomata in the leaves. (f) A small gap between the cells of the epidermis of a plant:- stoma Stomata are the pores in the plant epidermis that are surrounded by guard cells which control the opening and closing of the aperture. (g) A piece of apparatus used for measuring the rate at which a plant shoot takes up water:- potometer A piece of apparatus used for measuring the rate at which a plant shoot takes up water is called the potometer. The rate at which a plant takes up water depends on the rate of transpiration- the faster a plant transpires the faster it takes up water.

Give the correct technical term that matches each of these descriptions. (c) The collapse of leaves and shoots resulting from a loss turgor in the cells.

The collapse of leaves and shoots resulting from a loss turgor in the cells is called hypotonic. The process of plasmolysis is usually reversible. When the cells are placed in a hypotonic solution (higher water potential as compared to the cytoplasm), water diffuses into the cell causing the cytoplasm to build up a pressure against the wall that is called turgor pressure.