Reproduction in Animals Question Answers: NCERT Class 8 Science

Importance of reproduction in the organisms are as follows:

1. Reproduction is termed as the biological process in which organisms gives birth to the young ones or their offspring.
2. It helps in maintaining the continuity of a particular race and helps in increasing the population of the species.
3. Reproduction is meant for the survival of all living organisms.

Fusion of male and female gamete is called fertilization. Both male and female gametes are released by the reproductive organs of male and female body respectively. Sperm is released from the male reproductive organ, i.e. penis. These released sperms enter into the female body through vagina. Then through the vagina, sperms reaches to egg through the fallopian tube. The process of fertilization take place in the fallopian tube. 

(a)  (i) in the female body

Fertilization occurs internally as well as externally. External fertilization generally occurs in frogs, fishes etc.

(b)  (ii) metamorphosis

Due to drastic changes, larva changes into an adult, this process is known as metamorphosis.

(c)  (ii) one

Only one nuclei is present in a zygote.

(a) False

This statement is false because oviparous animals lay eggs and viviparous animals give birth to young ones.

(b) True

This statement is true because each sperm is a single cell and an egg is also a single cell.

(c) True

External fertilization takes place outside the female body; they lay eggs and then eggs got hatch and young ones are produced. So, this statement is true that external fertilization takes place in frogs.

(d) False

This statement is false because a new human individual develops not from a cell called gamete. A new individual is formed due to the fusion of two single cells i.e. sperm and egg.

(e) True

Yes, this statement is true because egg is a single cell.

(f) False

This statement is false because amoeba reproduce by binary fission. It is a type of asexual reproduction.

(g) False

This statement is false because fertilization only occurs in sexual reproduction, not in asexual reproduction.

(h) True

This statement is true because asexual reproduction is that in which only single parent is involved. Binary fission, budding are the types of asexual reproduction.

(i) True

Fusion of male and female gamete occurs and forms an zygote. This process of fusion is known as fertilization.

(j) False

This statement is false because embryo is formed by the repeated divisions of zygote or we can say that embryo is the mature zygote.  

Asexual reproduction may be defined as the reproduction in which only one parent is involved. The produced offspring is an exact copy of their parent or we can say identical to their parent.

Two methods of asexual reproduction in animals:

1. Binary fission: It is type of asexual reproduction in which a single cell divides into two halves. For example: Amoeba, bacteria etc.

In Amoeba, one nuclei is divided into two nuclei then the division of body occur in two halves. Each half of the amoeba gets a nuclei and produces new organism by each half.

          2. Budding: This is a type of asexual reproduction in which bulges arises from the parent body. For example: Hydra. The bulges are known as bud.

In Hydra, cells divide rapidly and some buds arise from specific site. These buds arise into a small individual when attached to the parent plant. When these becomes mature, they get detached from the parent body and become an independent individual.

The embryo gets embedded into the wall of the uterus. Embryo is the matured zygote. Development of various body parts like hands, head, eyes, legs etc. occur while the embryo still attached to the uterus. When the cells of body parts become identifiable then this is called as zygote.

A change in the animal’s body structure through the cell growth and the differentiation by which an animal develops after birth or hatching is known as metamorphosis. Or, we can say transforming of larva into an adult through a biological process is called as metamorphosis. Metamorphosis involved the sudden and abrupt changes in the structure of an animal. For example: frogs, insects etc.

Life cycle of Frog:

It involves mainly three stages:

Egg   →   Tadpole   →   Adult

From the egg tadpole emerges which have gills, tail and a small circular mouth. Tadpole can swim in water freely. Now some sudden and abrupt changes occurs in the structure of tadpole and it develops into a mature frog. The process of metamorphosis starts with the development and finally tail appearance occurs by the body.

Across

     1. FERTILIZATION
     6. INTERNAL
     7. BUDS
     8. OVARY

Down

     2. TESTES
     3. ZYGOTE
     4. OVIPAROUS
     5. BINARY

In Vitro Fertilisation

Test tube babies are born through IVF technique.

As a result of fertilisation zygote is formed which begins to develop into an embryo. The zygote divides repeatedly to give rise to a ball of cells. The cells then begin to form groups that develop into different tissues & organs of the body. This developing Structure is called an embryo. The embryo gets embedded in the wall of the uterus for further development.

There are mainly three distinct stages:

        Egg  →  Tadpole (larva)  →  Adultes 

Tadpole look different from the but after sometimes  tadpoles converted are into an frog.

In frogs, the gills of tadpoles are replaced by lungs in adults.

"IVF” is an artificial type of fertilization. Some  women's Oviducts are blocked. These women are unable to bear babies because sperms can't reach the egg for fertilisation 

In such cases, doctors collect Freshly released eggs, sperms & keep them together for few hours for IVF. In case fertilisation occurs, the zygote is allowed to develop for about a week & then it is placed in the mother's uterus .Complete development takes place in the uterus & the baby is born like any other baby Babies born through this technique are called test tube babies.