Fertilization:
(a) The process of fusion of male and female gamete is called fertilization or syngamy.
(b) The female gamete undergoes development to form 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. 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 takes place inside the body is called internal fertilization.
Zygote:
(a) Formation of zygote after fertilization is found in all sexually reproducing organisms.
(b) In case of external fertilization, zygote is formed usually in water.
(c) In case of internal fertilization, 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 haplontic life cycle, zygote undergoes meiosis to produce haploid spores.
Embryogenesis:
(a) The process of development of zygote into an embryo is called embryogenesis.
(b) Zygote undergoes cell division (mitosis) and cell differentiation.
(c) Oviparous are the animals which lay eggs and development takes place inside egg.
(d) Viviparous animals give birth to the young ones. The development takes place inside the body of the female.
(e) In plants:
(i) Zygote developed into embryo.
(ii) Ovule developed into seed
(iii) Integument of the ovule developed into seed coat.
(iv) Ovary developed into fruit.
(v) Ovary wall developed into pericarp.