KCSE 2016 Q7 USING A RELEVANT EXAMPLE IN EACH CASE, DESCRIBE SIMPLE AND CONDITIONED REFLEX ACTIONS. (20 MARKS)

-
Simple reflex action e.g. withdrawal of finger from a sharp object/ hot object;
  • Its an automatic response to a specific stimulus; when the finger touches sharp object/ hot object, the pain receptors/ thermo-receptors in the skin are stimulants; and trigger off a nerve impulse; the nerve impulse is transmitted via the senses neurone; to the grey matter of the spinal cord/ CNS/ brain; 
  • The impulse is then transmitted via synapse; to the relay neurone; and then through another synapse; to the motor neurone; the impulse is then transmitted to the effectormuscles in the  hand; [acc - Efferent neurone for motor neurone & Afferent neurone for sensory neurone, Intermediate/ associative/ connector/internuncial neurone - for relay].
  • The effector muscles/ biceps contract; and the finger is withdrawn from the hot object/ sharp  object; 
Conditioned reflex action - salivation in a dog/ human being (ace. any other relevant  example) student in response to sound; 
  • It is an automatic response evoked from an animal by unrelated stimulus; substituted for the one which normally elicits the response; 
  • It develops from a past experience; and involves modification of behaviour/involves learning; 
  • It weakens with time; and must be reinforced by repeating the related stimulus; 
  • The dog/ student salivates when the bell (for meals) rings; because they have learnt to associate the ringing of the bell at meal time with food; every time it rings (accept use of other relevant examples) they are offered food.

 20 MARKS

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