Class 8 Science NCERT Solutions for Chapter – 9 Reproduction in Animals

Reproduction in Animals

Question 1.
Explain the importance of reproduction in organisms.

Answer:
The production of new individuals from their parents is known as reproduction. Reproduction is very important as it ensures the continuation of a species. If the process of reproduction does not exist, the species would get vanished from the earth.

Question 2.
Describe the process of fertilization in human beings.

Answer:
The first step in the process of reproduction is the fusion of a sperm and an ovum. Millions of sperms from the male are transferred into the female body. The sperms swim in the oviduct with the help of their tails to reach the egg. When they come in contact with the egg, one of the sperms may fuse with the egg.

Such fusion of the egg and the sperm is called fertilization. During fertilization, the nucleus of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilized egg or zygote.

Question 3.
Choose the most appropriate answer.

(a) Internal fertilization occurs
1. In a female body.
2. Outside the female body.
3. In the male body.
4. Outside the male body.

Answer:
1. In a female body.

(b) A tadpole develops into an adult by the process of
1. Fertilization
2. Metamorphosis
3. Embedding
4. Budding

Answer:
2. Metamorphosis

(c) The number of nuclei present in a zygote is
1. None
2. One
3. Two
4. Four

Answer:
2. One

Question 4.
Indicate whether the following sentences are true (T) or false (F):

(a) Oviparous animals give birth to young ones.
Answer:
False

(b) Each sperm is a single cell.
Answer:
True

(c) External fertilization takes place in frogs.
Answer:
True

(d) A new human individual develops from a cell called gamete.
Answer:
False

(e) Egg laid after fertilization is made up of a single cell.
Answer:
True

(f) Amoeba reproduces by budding.
Answer:
False

(g) Fertilisation is necessary even in asexual reproduction.
Answer:
False

(h) Binary fission is a method of asexual reproduction.
Answer:
True

(i) A zygote is formed as a result of fertilization.
Answer:
True

(J) An embryo is made up of a single cell.
Answer:
False

Question 5.
Give two differences between a zygote and a fetus.

Answer:

ZygoteFetus
During, fertilization, the nuclei of the sperm and egg fuse to form a single nucleus. This results in the formation of a fertilized egg or zygote.The Zygote develops into an embryo, the embryo continues to develop in the uterus. It gradually develops 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 fetus.
 Zygote is single- celled.The Fetus is multi-celled.

Question 6.
Define asexual reproduction. Describe two methods of asexual reproduction in animals.

Answer:
The type of reproduction in which only a single parent is involved is called asexual reproduction.

Budding: The asexual reproduction in which an individual develops from buds, which is detached from a parent body is known as budding. For example, Hydra reproduces by this method. Many bulges are found in the parent body of hydra. These bulges called buds to develop into new individuals.
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Budding fission: It is a type of asexual reproduction in which an animal reproduces by dividing into two individuals. This type of reproduction is observed in the microscopic organism, amoeba. The reproduction in Amoeba begins by a division of its nucleus into two nuclei. This is followed by a division of its body into two with each part receiving a nucleus. Finally, two amoebae are produced from a single Amoeba.

Question 7.
In which female reproductive organ does the embryo get embedded?

Answer:
The embryo gets embedded in the wall of the uterus (of the female) for further development.

Question 8.
What is metamorphosis? Give examples.

Answer:
The drastic change which takes place during the development of an animal is called metamorphosis.
The animals that undergo metamorphosis are

  • Silkworm (egg → larva or caterpillar → pupa  → adult)
  • Frog (egg → tadpole larva → adult), etc.

Question 9.
Differentiate between internal fertilization and external fertilization.

Answer:

Internal fertilizationExternal fertilization
The fertilization that takes place inside the formal body is called internal fertilization.The fertilization that takes place outside the formal body is called external fertilization.
Few eggs are produced.Production of a large number of Eggs and sperms is necessary to ensure the fertilization of at least a few of them.
This is observed in human beings and other animals such as hen, cows, dogs, etc.This is observed in frogs, fish, starfish, etc.

Question 10.
Complete the crossword puzzle using the hints given below :

Across
1. The process of the fusion of the gametes.
6. The type of fertilization in the 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 fertilization.
4. These animals lay eggs.
5. A type of fission in Amoeba.

Answer:
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InText Questions and Answers

9.1 Modes of Reproduction

Question 1.
Have you seen the young ones of different animals? Try to name some of the young ones by completing Table 9.1 (Textbook page 100), shown in examples at S. No. 1 and 5.

Answer:

S.No.AnimalsYoung one
1.HumanBaby
2.CatKitten
3.DogPuppy
4.ButterfliesCaterpillars/Pupa
5.HenChick
6.CowCalf
7.FrogTadpole

Question 2.
Can you tell how chicks and caterpillars are born?

Answer:
The chicks and caterpillars are born out of sexual reproduction and hatched from the eggs so they are oviparous animals.

Question 3.
How are kittens and puppies born?

Answer:
These are also born out of sexual reproduction and born as babies so they are viviparous animals.

Question 4.
Do you think that these young ones looked the same before they were born as they do now?

Answer:
No. I don’t think so.

9,2 Sexual Reproduction

Question 5.
You will remember that plants that reproduce sexually have male and female reproductive parts. Can you name these parts?

Answer:
Yes, the stamen is the male reproductive part and the pistil is the female reproductive part of sexually reproducing plants.

Question 6.
What purpose does the tail in a sperm serve?

Answer:
The tail helps sperm to swim in the oviduct and to reach the egg for fertilization.

Activity 9.1

Question 1.
Have you ever seen a frog’s egg? Write down the color and size of the eggs.

Answer:
Yes, I have seen the color of the eggs is dull white and the size is less than a centimeter to a few centimeters.

Activity 9.2

Question 1.
Try to observe the eggs in some organisms. Make drawings of the eggs that you have observed.

Answer:
I have collected the eggs of frog, duck, butterfly, and hen. Drawings of these eggs are as under :
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Question 7.
Can you give some more examples of viviparous and oviparous animals?

Answer:
Examples of viviparous animals:

  • Elephant
  • Horse
  • Cow
  • Buffalo
  • Donkey
  • Monkey, etc.

Examples of oviparous animals :

  • Duck
  • Crow
  • Pigeon
  • Peacock
  • Cuckoo
  • Swan, etc.

Question 8.
Don’t the tadpoles look so different from the adults?

Answer:
Yes, they look quite different from the adults.

Question 9.
The caterpillars or the pupa of silkworm looks very different from the adult moth. The features that are present in the adult are not found in these young ones. Then, what happens to the tadpoles or caterpillars thereafter?

Answer:
In the case of a tadpole, a big young frog is developed in due course and they are capable of jumping and swimming. In the case of a caterpillar, it is first converted into a cocoon, from which a beautiful moth comes out.