KCSE 2018 ESSAY Q7 (A) DESCRIBE THE MODE OF REPRODUCTION IN A NAMED FUNGUS. (B) DESCRIBE THE ROLE OF HORMONES IN THE HUMAN MENSTRUAL CYCLE.

-
(a) Describe the mode of reproduction in a named fungus.
  • Rhizopus/mucor/ mould; reproduce a sexually; by sporulation; spores develop from a single in the sporangium; which burst on maturity releasing spores; which are dispersed by air currents/ wind; germinating to form new generation / form mycelium (if it lands on a suitable medium);
OR
  • Yeast/saccharomyces/ schizo saccharomyces ; reproduce asexually; by budding; parent cells form an out growth/projection/bud; followed by division of nucleus into two; one of the nuclei moves into the new bud; which grow and develops into a new cell; 
(7 marks Max 5)
(b) Describe the role of hormones in the human menstrual cycle.
  • After/at the onset of menstruation (the anterior lobe) of the pituitary gland; secretes follicle stimulating hormone (FSH); 
  • The FSH causes the Graafian follicle; to develop in the ovary; and stimulate the ovary tissues to secrete oestrogen hormone;
  • Oestrogen hormone brings about repair; healing of the endometrium; It's concentration increases to a level which stimulates the (anterior) pituitary gland; to secrete luteinising hormone (LH); and stops further secretion of FSH;
  • The LH stimulates maturation of the Graafian follicle; LH also stimulates the Graafian follicle to release an ovum (into the funnel of the fallopian tube)/ causes ovulation;
  • LH then stimulates the remains of the Graafian follicle to form a yellow body/ corpus luteum; (in the ovary).
  • The corpus luteum; is stimulated by the LH to produce progesterone;
  • Progesterone then stimulates the thickening of the endometrium/inner uterine wall; in readiness for implantation;
  • As progesterone level increases it Inhibits the pituitary gland from secreting FSH;
  • Further increase in progesterone level inhibits pituitary gland from secreting LH;.
  • It causes the corpus luteum to degenerate; (Rj disintegrate).
  • This reduces the amount of progesterone;
  • The sudden drop in secretion of progesterone causes endometrium to slough off/ menstruation occur; and the cycle is repeated.
(15 marks)
NB :Source of hormones must be mentioned as to score.

TOTAL 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