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Solutions for Science, Class 8, CBSE
Explain the importance of reproduction in organisms.
Reproduction is essential for the continuation of a species. It ensures the continuation of similar kinds of individuals, generation after generation and prevents them from becoming extinct.
Describe the process of fertilisation in human beings.
When sperms come in contact with an egg, one of the sperms may fuse with the egg. Such fusion of the egg and the sperm is called fertilisation. During fertilisation, the nuclei of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilised egg or zygote.
Internal fertilisation occurs
in female body
Reason — Fertilisation takes place inside the oviduct in the female body. Hence, it is called internal fertilisation.
A tadpole develops into an adult frog by the process of
metamorphosis
Reason — The transformation of the larva into adult through drastic changes is called metamorphosis. The tadpoles look like fish and are capable of swimming and transform into adults capable of jumping and swimming.
The number of nuclei present in a zygote is
one
Reason — During fertilisation, the nuclei of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilised egg or zygote.
Indicate whether the following statements are True or False.
(a) Oviparous animals give birth to young ones.
(b) Each sperm is a single cell.
(c) External fertilisation takes place in frog.
(d) A new human individual develops from a cell called gamete.
(e) Egg laid after fertilisation is made up of a single cell.
(f) Amoeba reproduces by budding.
(g) Fertilisation is necessary even in asexual reproduction.
(h) Binary fission is a method of asexual reproduction.
(i) A zygote is formed as a result of fertilisation.
(j) An embryo is made up of a single cell.
(a) False
Corrected statement — Viviparous animals give birth to young ones.
(b) True
(c) True
(d) False
Corrected statement — A new human individual develops from a cell called zygote.
(e) True
(f) False
Corrected statement — Amoeba reproduces by binary fission.
(g) False
Corrected statement — Fertilisation is not necessary in asexual reproduction.
(h) True
(i) True
(j) False
Corrected statement — A zygote is made up of a single cell.
Give two differences between a zygote and a foetus.
| Zygote | Foetus |
|---|---|
| Zygote is formed by the fusion of sperm and egg during fertilisation. | Foetus is the stage of the embryo in which all the body parts can be identified. |
| Zygote is unicellular. | Foetus is multicellular. |
Define asexual reproduction. Describe two methods of asexual reproduction in animals.
Asexual reproduction is the type of reproduction in which only a single parent is involved. It takes place by different methods like budding, binary fission etc.
Two methods of asexual reproduction in animals are:
In which female reproductive organ does the embryo get embedded?
The embryo gets embedded in the wall of the uterus of females for further development.
What is metamorphosis? Give examples.
The transformation of the larva into an adult through drastic changes is called metamorphosis. For example, it is seen in frog and butterfly. In frogs, there are three distinct stages, that is, egg, tadpole (larva) and adult. In butterfly the four distinct stages are egg, caterpillar, pupa and adult.
Differentiate between internal fertilisation and external fertilisation.
| Internal fertilisation | External fertilisation |
|---|---|
| It takes place inside the body of female. | It occurs outside the body. |
| It is observed in human beings and other animals such as hens, cows and dogs. | It is observed in aquatic animals and amphibians such as fish, starfish and frogs. |
| Lesser number of eggs are released. | Many more eggs are released. |
| Survival rate is higher. | Survival rate is low. |
Complete the crossword puzzle using the hints given below.
Across
1. The process of the fusion of the gametes.
6. The type of fertilisation in hen.
7. The term used for bulges observed on the sides of the body of hydra.
8. Eggs are produced here.
Down
2. Sperms are produced in these male reproductive organs.
3. Another term for in vitro fertilisation.
4. These animals lay eggs.
5. A type of fission in amoeba.
The solution of word puzzle is given below:
Across
1. Fertilisation.
6. Internal.
7. Buds.
8. Ovary.
Down
2. Testes.
3. IVF.
4. Oviparous.
5. Binary.
