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

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

DESCRIBE THE ADAPTATIONS OF THE ILEUM TO ITS FUNCTION (20 MARKS)

-
Has secretory glands/crypts of lieberkuhn which secretes enzymes (maltase/sucrase/lactase/peptidase/lipase to complete digestion of sugars/proteins/lipids. Goblet cells secrete mucus which allows for smooth movement of food and protect wall of ileum from action of digestive enzymes Very long to provide large surface area for absorption. Highly folded/coiled to slow movement of food to allow more time for digestion/absorption/ and to increase surface area for absorption. Has numerous villi which increase surface area for absorption/microvilli which further increase surface area for absorption. Ileum wall/villi have thin epithelium which is only one cell thick to reduce distance over which digested food has to diffuse. Villi are highly vascularised/have a rich network of blood capillaries for rapid transport from small intestines and maintain a steep concentration gradient for rapid absorption. Villi have lacteals for absorption of fatty acids and glycerol Cells of ileum wall h
Read more

(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