A) EXPLAIN THE FACTORS THAT AFFECT THE RATE OF TRANSPIRATION IN PLANTS. (12 mks) B) DESCRIBE DIFFERENT WAYS IN WHICH PLANTS RESPOND TO DIFFERENT STIMULI. (8 mks)

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 a) Explain the factors that affect the rate of transpiration in plants. (12 mks) 
  •  Higher temperature; increases the kinetic energy; of water molecules which makes water turn into vapour on the leaf surfaces faster and hence increase rate of transpiration.
  •  Higher light intensity; influences maximum opening of stomata which increases the surface area; over which transpiration occurs. 
  • Wind; carries away moisture around the plant and increases the capacity for air to hold water; which then increases the rate of water loss/transpiration in plants. 
  •  Higher relative humidity; reduces the capacity for air to hold water; which causes lowering of water loss/transpiration in plants. 
  • Higher amount of water in the soil; makes the plant to absorb excess water which increases the need for the plant to get rid of it through faster transpiration; 
  • If the leaf is broader and has numerous and larger open stomata; the surface area over which water loss occurs is increased; causing increase in the rate of transpiration. (award max. 12mks)
b) Describe different ways in which plants respond to different stimuli. (8mks) 
  •  Phototropism; causes plant shoots to grow by bending towards the direction of light source due to the migration of auxins to the non-exposed side where they cause faster growth; 
  • Geotropism; causes auxins to be highly concentrated on the lower surface of a root where they inhibit growth leading to a bend curvature towards gravity due to faster growth on the upper surface; 
  • Thigmotropism; enables the plants with weak stems to respond to contact by coiling around the supporting surface due to migration of auxins to the outer surface of the plant at the point of contact; 
  • Hydrotropism enables plant roots to grow towards the sources/direction of water in the soil; 
  • Thermotropism enables some plants to orient their growth towards the direction of higher temperatures; 
  • Chemotropism enables plant roots to grow by bending towards the direction of higher nutrients (chemicals) in the soil; this makes roots to absorb nutrients from the soil. (award max. 8mks)

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