Explain how abiotic factors affect plants. (20mks)

-
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

Comments

Post a Comment

Popular posts from this blog

(a) Define digestion. [2 m] (b) Describe the digestion of a piece of ugali in a human digestive system from the mouth until its assimilation. [18mks]

-
(a) Define digestion It is break down of complex insoluble; v food substance into simple soluble food substances; v 2max (b) Describe the digestion of ugali; Digestion of ugali begins in the mouth;v ugali is chewed by the teeth to increase large surface areav for action of salivary amylase / ptyalin; vThe food mixes with saliva produced by salivary glands;v Saliva contains mucus and enzyme ptyalin. Mucus moistens, softens and lubricates the food;v ptyalin speeds up the conversion of starch to maltose;v ugali is made into bolus in the mouth;v The bolus moves along the oesophagus and prestalsis / by contraction and relaxation of circular and longitudinal muscles into the stomach;v The digestion continues until ugali become acidic since the stomach does not contain carbohydrase / carbohydrate digesting enzymes no digestion of ugali takes place here.v Ugali now...
Read more

Explain how structures of the human ear are adapted to their functions. (20 marks)

-
Image
The pinna;- is funnel shaped to trap sound waves; cartilaginous to maintain the funnel shape; collects and directs sound waves into the external auditory meatus ear; The external auditory canal; - a tube connected to the pinna that directs sound waves from the pinna to the eardrum lining the auditory canal; has hair that trap foreign particles; The canal contains wax-secreting cells; and hair which traps dust particles; and pathogenic bacteria hence prevent them from getting into the ear; The eardrum; - has a thin tough membrane; that easily vibrates when hit by sound waves; transferring them into vibrations. The ear ossiscles; - they act like a layer and they easily move forward and backward to amplify sound vibrations that hit them; The suspensory ligaments; - suspends the ear ossicles and prevents excessive vibration that would otherwise damage the inner parts of the ear; The eustachian tube - it connects the middle ear with the pharynx; and it equalises air pressure between...
Read more

EXPLAIN HOW ABIOTIC FACTORS AFFECT PLANTS. (20MKS)

-
 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 photosynthesi...
Read more