Read the following statements.

I. Organisms exhibiting external fertilisation show great synchrony between the sexes and release a large number of gametes.

II. Amajor disadvantage of external fertilisation is that the offspring are extremely vulnerable to predators.

III. In gymnosperms, male gametes reach egg with the help of water as a medium.

IV. Zygote is a vital link that ensures continuity of species between organisms of one generation and the next.

V. Every sexually reproducing organisms begin their life as a single-celled zygote.

Which of the above statements are correct?