a) State any two functions of the placenta. (2mks) Describe the role of hormones in the human menstrual cycle. (18mks)

-
a) Two functions of the placenta
- serves for the exchange of materials between the mother and the foetus.
- Serves as endocrine organ- forms source of progesterone  hormone which is  important in female reproduction.

b) The role of hormones in the human menstrual cycle
the menstrual cycle begins on the very first day of the menstrual flow.
pituitary gland starts to secrete follicle stimulating hormone (FSH)
The FSH causes development of a Graafian follicle in the ovary. It also stimulates the walls of the follicle/tissues of the ovary to start secreting oestrogen.
Oestrogen causes repair and healing of the uterine wall.  It also stimulates the pituitary gland to secrete the lutenising hormone (LH)
 LH stimulates the final maturation of the Graafian follicle and ovulation.
Following ovulation, LH causes remains of the Graafina follicle to re-organize into a corpus luteum.
LH stimulates the corpus luteum to secrete the hormone progesterone.
Progesterone causes the lining of the uterus to get thickened, folded and invaded by blood vessels in readiness for implantation.
Progesterone and oestrogen also inhibit production of FSH which in turn prevents the development of another follicle and oestrogen production falls.
In the next two weeks after ovulation, progesterone level rises and inhibits production of LH from the pituitary gland.  The corpus luteum stops secretion of progesterone.  The sudden drop in the level  of progesterone causes menstruation to occur and the pituitary gland starts secreting FSH again.min;9 points;2 marks each.

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 photosynthesis.
Read more