Explain how abiotic factors affect plants. (20mks)

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Wind; on a windy day rate of transpiration increases since wind carries away water vapour   leaving surrounding of leaves with low humidity and increasing its ability to take water;
  • Wind disperse fruits, seeds/spore;
  • Wind is an agent of pollination
  • Strong winds break branches of trees and may uproot some trees;
Temperature; Enzymes work best at optimum temperature; hence influencing rate of photosynthesis/respiration; and other biological reactions.
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; when the humidity is high the atmosphere becomes
  •  saturated with water vapour reducing rate of transpiration;
pH; plants require optimum pH to grow well; acidic, alkaline or neutral
Salinity; - Plants with salt tolerant tissues; e.g. mangroves grow in saline areas.
  • - Plants in estuaries adjust to salt fluctuations;
  Water; - 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 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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