TRANSPIRATION Transpiration is the process through which plants loose water in form of water vapour mainly through the leaves.

Transpiration stream

stomata

Movement of water up the plant

Types of transpiration 1. stomatal transpiration 2. cuticular transpiration 3. lenticular transpiration

Factors affecting transpiration structural factors roots Plants with extensive root system have a high rate of transpiration than those with few roots. Extensive roots absorb more water hence more is available in the sub-stomatal spaces

Leaf size Large leaves have a large surface area over which transpiration takes place hence high rate of transpiration

Leaf structure Cuticle A thick cuticle reduces the rate of transpiration The cuticle in most case is waxy-wax reflect away the sunlight hence lower temperatures in the leaf Wax is also water proof hence reducing rate of transpiration

stomata -Number of stomata-the fewer the number of stomata the lower the rate of transpiration -Position of stomata-the sun shines directly on the upper surface of leaves hence increasing the rate of vapourization thus high water loss Stomata on the lower surface are sheltered from the suns rays hence lower water loss -Sunken stomata-when the stomata are sunken water vapour accumulates in the sub-stomatal air spaces thus its not exposed to moving air hence reducing the rate of transpiration

Leaf fall During periods of drought, some plants such as broad-leafed deciduous trees shed their leaves to reduce the surface area for water loss. In some species of grass the aerial shoot dries up to ground level. (e) Hairy leaves In some plant, leaves are covered with hairs or scales. These trap a layer of still moist air on the surface of the leaves thus reducing transpiration

prep Read and make notes on the environmental factors affecting transpiration