38. Discuss how the various tropisms adapt plants to their habitats .

-
Phototropism;  growth  curvature  in  response  to  direction  of  light;  enables  plant  shoots  to  grow and  get  light  for  maximum  photosynthesis;  allows  for  leaf  mosaic;  Thigmotropism;  growth curvature  in  response  to  contact/hard  surface;  makes  plants  with  weak  stems  to  get  support  on large  plant/trees;  this  makes  them  to  reach  and  get  light  for  maximum  photosynthesis; Geotropism;  growth  curvature  in  response  to  gravity;  enables  plant  roots  to  grow  deep  into  the soil  for  maximum  support/anchorage;  Hydrotropism;  growth  curvature  in  response  to moisture/water;  water  is  then  used  as  a  raw  material  during  photolysis  stage  of  photosynthesis; Chemotropism;  growth  curvature  in  response  to  chemical  concentration  gradient;  enables pollen  tubes  to  grow  down  the  style  and  into  the  ovary  for  fertilization  to  occur  in  plant flowers;  Thermotropism;  growth  curvature  in  response  to  temperature  changes;  enables  plants to  grow  to  where  they  can  acquire  optimum  temperature  for  effective  plant  process  (e.g. sunflower  orientates  towards  the  direction  of  the  sun);  Max.  20  mks 

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