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ncert class 8 science solution chapter 9
Class 8th Science Chapter 9 REPRODUCTION IN ANIMALS
NCERT Solutions Science for Class 8 Chapter 9 REPRODUCTION IN ANIMALS
science for class 8 Chapter 9 question answer
1. Explain the importance of reproduction in organisms.
Answer : reproduction is very important as it ensures the continuation of similar kinds of individuals, generation after generation. These processes are essential for the survival of every individual.
2. Describe the process of fertilisation in human beings.
Fertilisation : The first step in the process of reproduction is the fusion of a sperm and an ovum. 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.
The process of fertilisation is the meeting of an egg cell from the mother and a sperm cell from the father. So, the new individual inherits some characteristics from the mother and some from the father.
3. Choose the most appropriate answer.
|(a)||Internal fertilisation occurs|
|(i)||in female body.|
|(ii)||outside female body.|
|(iii)||in male body.|
|(iv)||outside male body.|
Answer : (i) in female body.
|(b)||A tadpole develops into an adult frog by the process of|
Answer : (ii) metamorphosis
|(c)||The number of nuclei present in a zygote is|
Answer : (ii) one
4. Indicate whether the following statements are True (T) or False (F).
|(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)||Oviparous animals give birth to young ones.||( F )|
|(b)||Each sperm is a single cell.||( T )|
|(c)||External fertilisation takes place in frog.||( T )|
|(d)||A new human individual develops from a cell called gamete.||( T )|
|(e)||Egg laid after fertilisation is made up of a single cell.||( T )|
|(f)||Amoeba reproduces by budding.||( F )|
|(g)||Fertilisation is necessary even in asexual reproduction.||( F )|
|(h)||Binary fission is a method of asexual reproduction.||( T )|
|(i)||A zygote is formed as a result of fertilisation.||( T )|
|(j)||An embryo is made up of a single cell.||( F )|
5. Give two differences between a zygote and a foetus.
Answer : two differences between a zygote and a foetus.
Zygote : 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. In which there is mainly a nucleus and the organs are not identified. The zygote divides repeatedly to give rise to an embryo.
Foetus : The stage of the embryo in which all the body parts are identifiable is called foetus. When the development of the foetus is complete, the mother gives birth to the baby.
6. Define asexual reproduction. Describe two methods of asexual reproduction in animals.
Asexual Reproduction – This type of reproduction in which only single parent involved is called asexual reproduction and gives rise to a new organism is called asexual reproduction.
Methods of Asexual Reproduction:
(i) Budding – In this type of reproduction each organism, there may be one or more bulges. These bulges are the developing new individuals and they are called buds. In hydra too the new individuals develop as outgrowths from a single parent. This type of reproduction in which only a single parent is involved is called asexual reproduction. Since new individuals develop from the buds in hydra, this type of asexual reproduction is called budding.
(ii) Binary fission – When the nucleus of an organism splits into two parts, it turns into two separate nuclei. This type of reproduction is called binary fission. 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. This type of asexual reproduction in which an animal reproduces by dividing into two individuals is called binary fission.
7. In which female reproductive organ does the embryo get embedded?
Answer : The embryo gets embedded in the wall of the uterus for further development.
8. What is metamorphosis? Give examples.
Metamorphosis : The transformation of the larva into an adult through drastic changes is called metamorphosis.
Example : a beautiful moth emerging out of the cocoon.
In the case of tadpoles, they transform into adults capable of jumping and swimming. The transformation of the larva into an adult through drastic changes is called metamorphosis. Many of the changes that we observe in our body as we grow.
9. Differentiate between internal fertilisation and external fertilisation.
Answer : Difference between internal fertilization and external fertilisation.
internal fertilisation : Fertilisation that takes place inside the female body is called internal fertilisation. This is observed in human beings and other animals such as hens, cows and dogs.
external fertilisation : Fertilisation that takes place outside the female body is called external fertilisation. This is observed in frogs, fish, starfish, etc.
10. Complete the crossword puzzle using the hints given below.
|The process of the fusion of the gametes.|
|The type of fertilisation in hen.|
|The term used for bulges observed on the sides of the body of hydra.|
|Eggs are produced here.|
|Sperms are produced in these male reproductive organs.|
|Another term for in vitro fertilisation.|
|These animals lay eggs.|
|A type of fission in amoeba.|