Science STD 8 Chapter 6: Reproduction in Animals - Exercises

Science STD 8 Chapter 6: Reproduction in Animals - Exercises

1. Explain the importance of reproduction in organisms.

Reproduction is essential for the continuation of a species. It ensures that similar kinds of individuals continue to exist generation after generation. Without reproduction, a species would eventually cease to exist. It is a fundamental process for the survival and propagation of all living organisms.

2. Describe the process of fertilisation in human beings.

In human beings, fertilisation is the process of fusion of a male gamete (sperm) and a female gamete (ovum). It is a type of internal fertilisation, as it occurs inside the female body. When sperms come in contact with an ovum, one sperm may fuse with the ovum. The nuclei of the sperm and the ovum fuse to form a single nucleus, which results in the formation of a fertilised egg or zygote. The zygote then develops into a new individual, inheriting characteristics from both parents.

3. Choose the most appropriate answer.

  1. (a) Internal fertilisation occurs
    1. in female body.
    2. outside female body.
    3. in male body.
    4. outside male body.
  2. (b) A tadpole develops into an adult frog by the process of
    1. fertilisation
    2. metamorphosis
    3. embedding
    4. budding
  3. (c) The number of nuclei present in a zygote is
    1. none
    2. one
    3. two
    4. four

4. Indicate whether the following statements are True (T) or False (F).

  1. (a) Oviparous animals give birth to young ones.

    F

  2. (b) Each sperm is a single cell.

    T

  3. (c) External fertilisation takes place in frog.

    T

  4. (d) A new human individual develops from a cell called gamete.

    F

  5. (e) Egg laid after fertilisation is made up of a single cell.

    T

  6. (f) Amoeba reproduces by budding.

    F

  7. (g) Fertilisation is necessary even in asexual reproduction.

    F

  8. (h) Binary fission is a method of asexual reproduction.

    T

  9. (i) A zygote is formed as a result of fertilisation.

    T

  10. (j) An embryo is made up of a single cell.

    F

5. Give two differences between a zygote and a foetus.

Zygote Foetus
It is a single cell formed by the fusion of a sperm and an ovum. It is the stage of an embryo in which all the body parts are identifiable.
It is the very first stage of development of a new individual. It is a later stage of development, where the embryo has grown and developed organs.
The zygote undergoes repeated cell division to form an embryo. The foetus is the developed form of the embryo with recognisable body parts.

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

Asexual reproduction is a type of reproduction in which only a single parent is involved to produce new individuals. The offspring produced are genetically identical to the parent. Two methods of asexual reproduction in animals are:

  • **Budding:** In this method, a new individual develops as an outgrowth or bud from a single parent. The bud detaches from the parent and grows into a new organism. This is seen in Hydra.
  • **Binary Fission:** This method of reproduction is seen in microscopic organisms like Amoeba. The parent organism divides into two new individuals. First, the nucleus divides, followed by the division of the body, with each part receiving a nucleus, thus forming two daughter amoebae.

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

The embryo gets embedded in the wall of the **uterus** for further development.

8. What is metamorphosis? Give examples.

Metamorphosis is the biological process by which a larva transforms into an adult through drastic changes. The young ones of some animals look very different from the adults. For example, a tadpole looks very different from an adult frog. During metamorphosis, the tadpole transforms into an adult frog that is capable of jumping and swimming. Other examples of animals that undergo metamorphosis are insects like butterflies and moths.

9. Differentiate between internal fertilisation and external fertilisation.

Internal Fertilisation External Fertilisation
It is the fusion of male and female gametes inside the female body. It is the fusion of male and female gametes outside the female body.
This process occurs in terrestrial animals. This process is common in aquatic animals.
Relatively fewer eggs and sperms are released. A large number of eggs and millions of sperms are released.
Examples: Humans, cows, hens. Examples: Frogs, fish, starfish.

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

Across

1. The process of the fusion of the gametes. FERTILISATION

6. The type of fertilisation in hen. INTERNAL

7. The term used for bulges observed on the sides of the body of hydra. BUDS

8. Eggs are produced here. OVARY

Down

2. Sperms are produced in these male reproductive organs. TESTES

3. Another term for in vitro fertilisation. EXTERNAL

4. These animals lay eggs. OVIPAROUS

5. A type of fission in amoeba. BINARY

Suggested Activities and Projects

1. Visit a poultry farm. Talk to the manager of the farm and try to find out the answers to the following. (a) What are layers and broilers in a poultry farm? (b) Do hens lay unfertilised eggs? (c) How can you obtain fertilised and unfertilised eggs? (d) Are the eggs that we get in the stores fertilised or unfertilised? (e) Can you consume fertilised eggs? (f) Is there any difference in the nutritional value of fertilised and unfertilised eggs?

Outline: This activity involves a field trip to a poultry farm to learn about egg production. You would learn that layers are hens raised for laying eggs, while broilers are raised for meat. Hens can lay unfertilised eggs without a male (rooster) present. The eggs sold in stores are generally unfertilised and are safe to eat. Fertilised eggs, however, can be incubated to hatch a chick. There is no significant nutritional difference between fertilised and unfertilised eggs.

2. Observe live hydra yourself and learn how they reproduce by doing the following activity: During the summer months collect water weeds from ponds or ditches along with the pond water and put them in a glass jar. After a day or so you may see several hydra clinging to the sides of the jar. Hydra is transparent, jelly-like and with tentacles. It clings to the jar with the base of its body. If the jar is shaken, the hydra will contract instantly into a small blob, at the same time drawing its tentacles in. Now take out few hydras from the jar and put them on a watch glass. Using a hand lens or a binocular or dissection microscope, observe the changes that are taking place in their body. Note down your observations.

Outline: This is a hands-on activity to observe asexual reproduction in Hydra. By collecting and observing live Hydra, you would see the formation of small bulges or buds on the parent body. These buds would grow and eventually detach to form new individuals. This visual observation would help you understand the process of budding in animals.

3. The eggs we get from the market are generally the unfertilised ones. In case you wish to observe a developing chick embryo, get a fertilised egg from the poultry or hatchery which has been incubated for 36 hours or more. You may then be able to see a white disc-like structure on the yolk. This is the developing embryo. Sometimes if the heart and blood vessels have developed you may even see a red spot.

Outline: This activity is about observing the early stages of embryo development. By examining a fertilised, incubated egg, you would be able to see a small, white disc on the yolk, which is the embryo. This project provides a unique opportunity to observe the early stages of life and understand the process of embryo development in oviparous animals.

4. Talk to a doctor. Find out how twinning occurs. Look for any twins in your neighbourhood, or among your friends. Find out if the twins are identical or non-identical. Also find out why identical twins are always of the same sex? If you know of any story about twins, write it in your own words.

Outline: This activity involves researching and interviewing a doctor to understand the biological process of twinning. You would learn that identical twins result from a single fertilised egg splitting into two, so they are always the same sex. Non-identical twins result from two separate eggs being fertilised by two separate sperms, so they can be of different sexes. The project would also involve a small survey of twins in your neighbourhood to identify whether they are identical or non-identical.