Sexual Reproduction: Fertilisation Events
Fertilisation is the most important event in sexual reproduction.
This process is also called syngamy and leads to the formation of the zygote. However, in some organisms, zygote formation takes place without fertilisation, and is known as parthenogenesis (occurs in rotifers, honeybees and some lizards).
In most aquatic organisms and amphibians, Fertilisation takes place outside their body (in the water), and is termed as external fertilization. Their eggs and offspring are highly vulnerable to predators and this threatens their survival up to adulthood.
In most terrestrial organisms, fertilisation is internal, i.e., it takes place inside the female body. In this process, the male gamete is motile and reaches the female gamete to fuse with it, thereby forming zygote. Male gametes are produced in large numbers.