Reproduction in Animals

Q44. How does fertilization take place in frog?
Or
How do frog eggs get fertilized?
Or
How does fertilization occur in frog?

Ans. During spring or rainy season, frogs and toads move to ponds and slow flowing streams. When the male and female come together in water, the female lays hundreds of eggs. Frog’s egg is not covered by a shell and it is comparatively very delicate. A layer of jelly holds the eggs together and provides protection to the eggs. As the eggs are laid, the male deposits sperms over them. Each sperm swims randomly in water with the help of its long tail. The sperms come in contact with the eggs. This results in fertilization.

Q45. What is ‘in vitro fertilization’ technique of reproduction?
Or
What are test-tube babies?

Ans. In some women oviducts are blocked. These women are unable to bear babies because sperms cannot reach the egg for fertilization. In such cases, doctors collect freshly released egg and sperms and keep them together for a few hours for IVF or in vitro fertilization (fertilization outside the body). In case fertilization occurs, the zygote is allowed to develop for about a week and then it is placed in the mother’s uterus. Complete development takes place in the uterus and the baby is born like any other baby. Babies born through this technique are called test-tube babies.

Q46. How could a single cell become such a big individual?

Ans. Fertilization results in the formation of zygote. The zygote divides repeatedly to give rise to a ball of cells. The cells then begin to form groups that develop into different tissues and organs of the body. This developing structure is termed an embryo. The embryo gets embedded in the wall of the uterus for further development. The embryo continues to develop in the uterus. It gradually develops the body parts such as hands, legs, head, eyes, ears, etc. The stage of the embryo in which all the body parts can be identified is called a foetus. When the development of the foetus is complete, the mother gives birth to the baby.

Q47. What are the steps involved in sexual reproduction in animals?

Ans. Steps involved in sexual reproduction in animals are:

                            i.        The male parent produces male gametes called sperms. Sperm is a single cell with all the usual cell components.

                           ii.        The female parent produces female gametes called eggs (or ova). Like the sperm, an egg is also a single cell.

                          iii.        The sperm enters into the egg. The nucleus of sperm fuses with the nucleus of egg cell to form a new cell called zygote.

                          iv.        The zygote divides repeatedly to form a hollow ball of hundreds of cells which is called embryo.

                           v.        Embryo grows and becomes a foetus in which all main body features of the baby animal have formed.

                          vi.        Foetus grows and develops to form a new baby animal.

Q48. How does an amoeba reproduce?

Ans. Amoeba is a single-celled organism. It begins the process of reproduction by the division of its nucleus into two nuclei. This is followed by division of its body into two, each part receiving a nucleus. Finally, two amoebae are produced from one parent amoeba.

Image from NCERT