Chapter 4: Reproduction and Growth

• Reproduction is carried out by all living things to produce off spring, to increase in numbers so as to ensure the continuation of the species.
• Spermatogenesis is the production of sperm.
• It occurs in the seminiferous tubules inside the testes.
• Oogenesis it the production of ovum.
• It occurs in the ovary.
• Sperm and ovum are gametes.
  
• The importance of gametes formation in human are they maintain the diploid chromosomal number (2n) from one generation to another and they produce genetic variation in the next generation.
• The menstrual cycle is a repeated pattern of ovulation and changes in the uterine wall that occurs approximately every 28 days when a female reaches puberty. It is under the control of hormones.
• During the menstrual cycle, there is discharge of blood, breakdown of tissue from the uterine wall and loss of the unfertilised ovum. This process is called menstruation.
• Ovulation is the release of the ovum from the Graafian follicle between the thirteen to fifteenth day of the menstrual cycle.
• The pituitary gland prouduces two hormones, the follicle-stimulating hormone (FSH) and the luteinising hormone(LH).
• FSH stimulates the development of the follicle in the ovary.
• LH stimulates ovulation and the formation of the corpus luteum.
• Oestrogen is a hormone produced by follicle cell.
• Progesterone is prouduced by the corpus luteum.
• Oestrogen and progesterone are responsible for the repair and thickening of the endometrium after menstruation.
• Menopause usually occurs at the age of about 50.
• No new ovarian follicles will be developed after menopause.
• Ovarian activity will cease.
  
• Fertilisation between a sperm and ovum occurs in the Fallopian tube.
• It results in the formation of a zygote.
• The zygote undergoes repeated cell division to form a morula, blastocyst and finally an embryo.
• Implantation occurs in the blastocyst stage.
• The placenta is an organ made up of matrnal and foetal tissues.
• The placenta is the place where exchange of nutrients, oxygen and waste material between the mother's blood and the foetal occurs.
• Identical twins are produced when one ovum is fertilised by one sperm to form a zygote which then divides to form two embryos.
• Identical twins have the same genetic composition and are of the same sex.
• Fraternal twins are produced from two ova fertilised by two different sperms.
• They have different genetic composition and may be of the same and different sexes.
• Infertility problems ca be overcome by artificial insemination, in vitro fertilisation and surrogate motherhood.
• Unwanted pregnancies can be prevented by temporary methods such as using condoms, rhythm method, IUD and contraceptive pills.
• It can also be prevented by permanent ssuch as vasectomy and female sterilizations.
• Flower is the reproductive organ in plant.
  
• Double fertilisation involves the fusion of one male gamete with an ovum to form a zygote(2n) and another fusion with another male gamete with two polar nuclei to produce the endosperm nucleus (3n)
• Growth is the irreversible increase in body size, mass and the number of cells in an organism and it involves a change in shape, form, function and complexity.
• The growth curve of most organisms is sigmoid in shape (S-shaped).
• For the insect, the growth curve is like a series of steps and corresponds to the instars in the insect 's development.
• Growth in plants involves rapid cell division and elongation at specific region known as meristem.
• There are two types of meristem, apical and lateral meristems.
  
• Primary growth in plants take place at the root tip and the shoot tip.
• Primary growth results in an increase in height of the shoot and an increase in length of the root.
• Secondary growth involves the vascular cambium and the cork cambium which divide and increase the girth of the stem.