Notes of Reproduction in animals
Answers
The modes of reproduction are based on the requirements of the number of parents, which are:
(i). Sexual reproduction
(ii). Asexual reproduction
In sexual reproduction, the species consist of male and female reproductive organs. The kind of reproduction in which the fusion of male and female gametes takes place is called sexual reproduction.
The female reproductive organs include ovaries, oviducts, and uterus whereas the reproductive organs in the male include testes, sperm ducts, and penis. The ovary produces female gametes called ova (egg cells) and the testes produce male gametes called sperms.
The fusion of these gametes (ovum and sperm) is called fertilization. The egg developed after fertilization is called a zygote.
The fertilization can occur inside or outside the parent body, so it is divided into two types:
The fertilization taking place inside the body of female species is called internal fertilization. This phenomenon is observed in human beings and other animals, for example, hens, cats, dogs, and other mammals.
The fertilization taking place outside the body of the female species is called external fertilization. This is generally observed in aquatic animals such as frogs, fish, etc.
After fertilization, a zygote is formed, which begins to develop into an embryo. The zygote divides itself repeatedly which results in an embryo, which then gets embedded in the wall of the uterus and develops into body parts. The stage when the embryo develops well-defined body parts is called the foetus.
Organisms such as humans, cats, cows, and other mammals which give birth to young ones are called viviparous animals.
Egg-laying animals are called oviparous animals, e.g., frogs, lizards, butterflies, etc.
In metamorphosis, the larva is transformed into an adult. It is not observed in humans but it is observed in insects like butterflies, silkworms, frogs, etc.
This is the type of reproduction in which only a single parent is required. Such a type of reproduction is called asexual reproduction. Species like hydra, amoeba, and other microscopic unicellular organisms.
In hydra, new individuals develop from buds formed from the parent body. This method of asexual reproduction by forming buds is called budding.
When an organism reproduces by dividing itself into two from a single parent, this type of asexual reproduction is called binary fission. For example, microscopic organisms like amoeba reproduce by dividing themselves into two. In this method the organism divides its nucleus into two parts, thus each part contains a nucleus.