EXPLAIN HOW ABIOTIC FACTORS AFFECT PLANTS. (20MKS)

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 Explain how abiotic factors affect plants. (20mks)

Abiotic factors.
Wind;
-On a windy day rate of transpiration increases since wind carries away water vapour leaving surrounding of leaves with low humidity; the lower the humidity the more the space in the atmosphere for water molecules to occupy.
- Wind disperse fruits, seeds and spore;
- Wind is an agent of pollination.
- Strong winds break branches of trees and may even uproot some trees;

Temperature;
-Enzymes work best at optimum temperature; changes in temperature hence influence rate of photosynthesis/respiration; and other enzyme controlled biological reactions.
-In aquatic environment temperature affects the percent of dissolved gases.

Light;
- green plants need light for photosynthesis;
- some plants need light for flowering; photoperiodism;
- some seeds (lettuce) require light for germination;
- light affects opening and closing of stomata; which affects transpiration; gaseous exchange and photosynthesis.

Humidity;
-When humidity is low the rate of transpiration increases due to less amount of
 water vapour in the atmosphere hence more spaces for water vapour molecules to occupy; when the humidity is high the atmosphere becomes saturated with water vapour reducing the space available for water molecules to occupy hence rate of transpiration;

 pH;
-Plants require optimum pH to grow well; acidic, alkaline or neutral; enzymes that control biological reactions are affected by pH

Salinity;
- Plants with salt tolerant tissues; e.g. mangroves grow in saline areas
- Plants in Estuaries adjust to salt fluctuations;

Water;
- Needed for germination;
-For photosynthesis;
-Transport medium for synthesized food;
-It is a solvent dissolving mineral salts for absorption and transport;
-Water increases turgidity of cells hence offers mechanical support;
-Water disperses fruits and seeds;
-Aquatic plants need water for pollination;
-Pteridophyta and bryophyta need water during fertilization;

Topography;
-Windward side receives enough rainfall and plants grow well;
-The leeward side receives less rainfall resulting into plants with stunted growth; north facing slopes
 in the southern hemisphere have more growth of plants.

Max 20mks

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