(a) The process of fusion of male and female gamete is called fertilization or syngamy.
(b) The female gamete undergoes development to form a new organism without fertilization. This phenomenon is called parthenogenesis. It is a modification of sexual reproduction.
(c) Gametic fusion taking place outside the body i.e. water is called external fertilization.
(d) There must be synchrony of gamete release. A large number of gametes is released to enhance the chance of fertilization.
(e) A major disadvantage is that the offsprings are extremely vulnerable to predators.
(f) Fertilization that takes place inside the body is called internal fertilization.
(a) Formation of zygote after fertilization is found in all sexually reproducing organisms.
(b) In the case of external fertilization, the zygote is formed usually in water.
(c) In the case of internal fertilization, the zygote is formed inside the body of the organism.
(d) Zygote of fungi and algae develops a thick wall that is resistant to desiccation and damage.
(e) Organism with the haplontic life cycle, the zygote undergoes meiosis to produce haploid spores.
(a) The process of development of a zygote into an embryo is called embryogenesis.
(b) Zygote undergoes cell division (mitosis) and cell differentiation.
(c) Oviparous are the animals that lay eggs and development takes place inside the egg.
(d) Viviparous animals give birth to young ones. The development takes place inside the body of the female.
(e) In plants:
(i) Zygote developed into an embryo.
(ii) Ovule developed into seed
(iii) Integument of the ovule developed into the seed coat.
(iv) Ovary developed into fruit.
(v) Ovary wall developed into pericarp
Pituitary Gland (Hypophysis)
(1) Pituitary is known as hypophysis cerebri, its name pituitary was given by Vesalius.
(2) Muller’s gland of amphioxus and subneural gland of hardmania is homologous to the pituitary of vertebrates.
Parts and component
(1) Adenohypophysis (Anterior lobe)
(i) Pars distalis
(ii) Pars tuberalis
(iii) Pars intermedia
(2) Neurohypophysis (Posterior lobe)
(i) Pars nervosa
(i) Position and Structure: Hypothalamus is the floor of the diencephalon. It is formed of masses of grey matter, called hypothalamic nuclei, containing neurosecretory cells. It is connected with the anterior pituitary lobe by blood capillaries of the hypophyseal portal system and with the posterior pituitary lobe by axons of its neurons, both passing through the pituitary stalk.
(ii) Hormones of the hypothalamus: Neurosecretory cells of the hypothalamus secrete neurohormones called releasing factors (RF) or inhibiting factors (IF). These neurohormones are carried by the hypophyseal portal system to adenohypophysis (primary target organ) and stimulate or inhibit the release of trophic hormones from the adenohypophysis. These neurohormones are proteinous in nature and formed of 3 – 20 amino acids
1) Hormones of parathyroid: Active hormone secreted by parathyroids is parathormone (PTH), also called Collip’s Hormone (Phillips collie, 1925).
(2) Irregularities of parathormones
(a) Hypoparathyroidism (Hyposecretion of parathormone)
(b) Hyperparathyroidism (Hypersecretion of parathormone)
(1) Hormones of the pancreas and their role:
(a) Insulin: Insulin regulates how the body uses and stores glucose and fat.
(b) Glucagon: This is secreted by the alpha cells of islets of Langerhans. Its function is to elevate glucose levels in blood when glucose is deficient.
(c) Somatostatin and Pancreatic polypeptide: Modern physiologists have postulated that the d and F (PP) cells of the pancreas respectively secrete somatostatin (SS) and pancreatic polypeptide (PP). Somatostatin resembles the growth hormone inhibitory hormone (GHIH) secreted by the hypothalamus.
(1) Function of thymus glands
(a) Thymus is haemopoietic, as well as, an endocrine gland.
(b) The major function of the thymus is to secrete thymosin hormone, thymic humoral factor (THF), thymic factor (TF), thymopoietin.
(c) Thymus is essential in neonatal (newly born) infant and postnatal children for normal development of lymphoid organs and cellular immunity.
(1) The gonads are the sex glands, the testes and the ovary.
The testis forms part of the male reproductive system and is the gland where sperm and testosterone are produced.
Functions of Testes
(a) It stimulates the male reproductive system to grow to full size and become functional.
(b) It stimulates the formation of sperms (spermatogenesis) in the seminiferous tubules.
(c) It also determines the male sexual behaviour sex urge, aggressive behaviour.
(d) Under its effect protein anabolism increases.