Organisms that take part in such process produce large number of gametes because

(i) In external fertilisation, there is a great chance that the sperm and the eggs released by the organisms can be affected by factors present in the environment like dessication, predators, etc. So, to make up for the high fatality rate of the gametes, the organism produces a lot of gametes.

(ii) Producing large number of gametes increase the chance for at least some eggs and sperms to meet in the environment ensuring that atleast a stable number of offspring are able to survive and carry on.

(a) Earthworm- Monoecious animal

(b) Chara-Monoecious plant

(c) Marchantia-Dioecious plant

(d) Cockroach- Dioecious animal

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In plants, the units of vegetative propagation such as runner, rhizome, sucker, tuber, offset, bulb are all capable of giving rise to new offsprings. These structures are called vegetative propagules.

(a) Ovary .............. fruit

(b) Ovules ............ seed

After fertilisation, the zygote develops into the embryo and the ovules develop into the seed. The ovary develops into the fruit which develops a thick, protective wall called pericarp.

Meiosis can take place only in a diploid stage (post-zygotic stage) because the zygote is the only diploid cell in the life cycle of such organisms. This meiosis an case of haploid organisms will occur of the fertilisation.