a) Define a reflex action (2mks) b) Using a diagram describe what happens in the nervous system of a person who withdraws a finger from a very hot object (18mks)

-
a) Define a reflex action (2mks)
  • Is a rapid automatic response to a certain stimulus
A – sense organ (Receptor)
B – Sensory neurone
C – Relay neurone
D – Synapse
E – Motor neurone
F – Effector organ
b) Using a diagram describe what happens in the nervous system of a person who withdraws a finger from a very hot object (18mks)
Image result for REMOVING A FINGER FROM A HOT OBJECT REFLEX ARC
  • When the finger touches a very hot object; pain receptors; in the skin of the finger
  • are stimulated;
  • Nerve impulses are triggered off; and transmitted through the sensory neurone; to grey matter of the spinal cord;
  • The impulse is then transmitted to the relay neurone; through the synapse; then to the motor
  • neurone; through another synapse;
  • Through the ventral root, the impulse is transmitted to the effector organ (bicep of the arm); which contracts; and the forearm is withdrawn; and thus the finger is raised from the hot object;

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