K.C.S.E Biology Q & A - MODEL 2019PP2QN05

K.C.S.E Biology Q & A - MODEL 2019PP2QN05

 A person accidentally touches a hot pan and responds as illustrated in the diagram below.

(a) Explain how the response illustrated above occurs. 
(b) Explain how auxins are utilised as selective weed killers in agriculture.

answers

• ​(a) The stimulus /heat/pain is detected by temperature/pain receptor( Thermo receptors) in the skin/dermis; An impulse is generated; impulse is transmitted along a sensory neurone to the CNS/spinal cord; (chemical) transmission across synapse to relay neurone; Across a synapse to motor neurone; across a synapse to biceps muscles,/effector via motor neurone; muscles/effectors contracts; (hand moves away). This is known as (simple reflex action);              
  
• Stimulus/pain/temperature detector
• Receptor-impulse-sensory neurone-synapse-relay neurone (CNS)-synapse-motor neurone-    synapse-biceps-control.
• (b) Selective weed killer contains auxins which are absorbed by the weeds (than desired/ beneficial plants); making the weeds to grow abnormally/accelerated die out; (weed of the beneficial plants);