Ch 1Reproduction in Organisms — Class 12 Biology, concept-first.

Whatever an organism's life span, death is inevitable for every individual — except, notably, single-celled organisms, which do not undergo a natural death in the same sense because the parent cell si…

Despite the enormous diversity among plants, animals and fungi in body form, internal structure and physiology, their sexual reproduction follows a broadly similar pattern.

- Gametogenesis — the production of the male and female gametes themselves, through cell division within the reproductive organs or structures of the parent organism(s).

Among animals, most species are unisexual — the cockroach, for instance, exists as separate male and female individuals (Figure 1.6b), each with only testes or only ovaries.

Gamete Transfer Once male and female gametes have formed, they must be physically brought together before they can fuse — this movement is called gamete transfer.

Fertilisation The single most important event in sexual reproduction is the fusion of the male and female gametes.

Two closely linked processes make up this stage: - Formation of the zygote — the diploid cell created immediately by fertilisation, whose further fate depends on the kind of organism and the environme…

The Zygote The formation of a diploid zygote by the fusion of gametes is a universal feature of sexual reproduction, found in every sexually reproducing organism.

Because viviparous young receive continuous embryonic care and protection inside the parent's body, their survival chances are generally much higher than those of oviparous young, whose eggs and hatch…

Sexual reproduction, the near-universal strategy in higher animals, is slower and more complex because it depends on the formation and fusion of gametes from (typically) two parents, producing genetic…