What is transpiration? Explain its types, the factors affecting it and its significance.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define in one line. Transpiration is the loss of water as vapour from the aerial parts of a plant.
2 · Types.
Stomatal: through the stomata; the most.
Cuticular: through the cuticle.
Lenticular: through the lenticels in bark.
3 · Draw a stoma. [An open and a closed stoma: two guard cells, the pore, chloroplasts and the nearby epidermal cells]
4 · Factors.
Light, temperature and wind increase it.
Humidity decreases it; a shortage of soil water reduces it.
Leaf structure: sunken stomata and a thick cuticle reduce it.
5 · Significance. Creates transpiration pull, helps distribute minerals, cools the plant and removes excess water; too much causes wilting (a necessary evil).
6 · Real life. Shade trees such as neem cool the air around them by transpiration.
7 · Close in one line. Transpiration is a water loss the plant cannot avoid, but it puts it to good use.
Scoring tip: For each factor, write one line saying whether it raises or lowers the rate; that wins the factor marks quickly.
