Post- fertilization events
- In some organisms like fungi and algae, the zygote develops a thick wall around it which is resistant to damage and undergoes a period before germination.
- Further development of zygote depends on the type of life cycle of organisms and the environment in which they are surviving.
- In all sexually reproducing organisms, a diploid zygote is formed as a result of fertilization and later the zygote develops into a new organism.
- The process of development of embryo from the zygote is called embryogenesis.
- Embryogenesis includes cell division and cell differentiation in the zygote.
- Cell division increases the number of cells and cell differentiation helps to form tissues and organs to form a fully developed organism.
- Depending on the development of zygote inside or outside the body of the female parent, animals are classified into oviparous and viviparous animals.
- Oviparous animals are those which lay eggs and the eggs develop into new organisms. Example- amphibians, fishes, birds, reptiles etc.
- Viviparous animals are those which give birth to their young ones. Example- mammals.
- In some oviparous animals like reptiles and birds the fertilized eggs remain covered by hard calcareous shell and such eggs are called cleidoic
- In flowering plants, the zygote is formed inside the ovule and the sepals, petals, stamens of the flower usually fall off.
- The zygote develops into embryo
- Ovules develop into seeds
- The ovary develops into the fruit.
- The ovary wall develops into a protective layer called pericarp.
Fig. fruit and seed formation