SECONDARY SEXUAL CHARACTERISTICS - k.c.s.e biology notes

​Male

• Testerone is the main androgen that stimulates the development of secondary sexual characteristics.
• Broadening of the shoulders.
• Deepening of the voice due to enlargement of larynx.
• Hair at the pubic area, armpit and chin regions.
• Penis and testis enlarge and produce sperms.
• Body becomes more masculine.

Female

• Enlargement of mammary glands.
• Hair grows around pubic and armpit regions.
• Widening of the hips.
• Ovaries mature and start producing ova.
• Menstruation starts.
• Oestrogen triggers the onset of secondary sexual characteristics. 

​Sexually transmitted infections (STl)

Menstrual Cycle

• This is characterized by discharge of blood and tissue debris (menses) from the uterus every 28 days.
• This is due to the breakdown of the endometrium which occurs when the level of progesterone falls and the girl starts to menstruate.
• The follicle stimulating hormone (FSH) causes the Graafian follicle to develop and also stimulate the ovary to release oestrogen.
• Oestrogen hormone triggers the onset of secondary sexual characteristics.
• Luteinising hormone (L.H) causes the mature ovum to be released from the Graafian follicle - a process called ovulation.
• After ovulation progesterone hormone is produced.
• After menstruation, the anterior lobe of the pituitary gland starts secreting the follicle stimulating hormone (FS.H) which causes the Graafian follicle to develop in the ovary.
• It also stimulates the ovary tissues to secrete oestrogen.
• Oestrogen brings about the repair and healing of the inner lining of the uterus (endometrium) which had been destroyed during menstruation.
• Oestrogen level stimulates the pituitary gland to produce (Luteinising Hormone (L.H).
• This hormone makes the mature Graafian follicle to release the ovum into the funnel of oviduct, a process called ovulation.
• After releasing the ovum, the Graafian follicle changes into a yellow body called corpus luteum.
• The luteinising hormone stimulates the corpus luteum to secrete a hormone called progesterone which stimulates the thickening and vascularisation of endometrium.
• This prepares the uterine wall for implantation of the blastocyst.
• If fertilisation takes place, the level of progesterone increases and thus inhibits FSH from stimulating the maturation of another Graafian follicle.
• If fertilisation does not occur, the corpus luteum disintegrates and the level of progesterone goes down.
• The endometrium, sloughs off and menstruation occurs.

Advantages of Reproduction Asexual

• Good qualities from parents are retained in the offspring without variation.
• New individuals produced asexually mature faster.
• Process does not depend on external factors which may fail such as pollination.
• New individuals obtain nourishment from parent and so are able to survive temporarily under unsuitable conditions.
• No indiscriminate spreading of individuals which can result in wastage of offspring.
• Takes a shorter time and leads to rapid colonization.

Disadvantages of asexual reproduction

• New offspring may carry undesirable qualities from parents.
• Offspring may be unable to withstand changing environmental conditions.
• Faster maturity can cause overcrowding and stiff competition.
• Reduced strength and vigour of successive generations. 

Advantages of sexual reproduction

• Leads to variations.
• Variations which are desirable often show hybrid vigour.
• High adaptability of individuals to changing environmental conditions.
• Variations provide a basis for evolutionary changes.

Disadvantages of sexual reproduction

• Fusion is difficult if two individuals are isolated.
• Some variations may have undesirable qualities.
• Population growth is slow.

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