NCERT Solutions Class 10 Science Chapter 8

Q.1 Asexual reproduction takes place through budding in

1. amoeba.
2. yeast.
3. plasmodium.
4. leishmania.

b. Yeast

Explanation: Out of the four organisms mentioned, only in yeast asexual reproduction takes place though budding. Asexually Amoeba and Leishmania reproduce through binary fission and Plasmodium reproduces by multiple fission method.

Q.2 Which of the following is not a part of the female reproductive system in human beings?

1. Ovary
2. Uterus
3. Vas deferens
4. Fallopian tube

Vas deferens

Explanation: Ovary, uterus and fallopian tube are the parts of the female reproductive system in human beings whereas vas deferens is the part of male reproductive system in human beings.

Q.3 The anther contains

1. sepals.
2. ovules.
3. carpel.
4. pollen grains.

d) Pollen grains

Explanation: The anther contains pollen grains. Sepals are generally green in colour and protect flower in bud stage. Ovules are present in ovary of the carpel (female reproductive organ of plant).

Q.4 What are the advantages of sexual reproduction over asexual reproduction?

Advantages of sexual reproduction over asexual reproduction are:

1. Sexual reproduction is responsible for variations in a population.
2. Variations in individuals are responsible for survival of a species in an ecosystem.
3. Sexual reproduction plays an important role in origin of new species and is a beginning for evolution.
4. Sexual reproduction helps in providing stability to populations of species.

Q.5 What are the functions performed by the testis in human beings?

Testes are the male reproductive organs in human beings. Functions of testis are:

1. It produces male gametes i.e., sperms.
2. It also produces male hormone called testosterone that regulates the formation of sperms and is responsible for secondary sexual characters in human males at the time of puberty.

Q.6 Why does menstruation occur?

Menstruation is a process in which blood and mucosal tissues are discharged periodically from the inner lining of uterus through the vagina. In human female, every month one egg is released from one ovary. Simultaneously the uterus prepares itself for pregnancy. During this phase, the inner lining of the uterus gets thickened and new blood vessels are formed that will nourish the future embryo. If pregnancy does not occur, then the lining of the uterus breaks down slowly and the content is released in the form of blood and mucus through the vagina and the process is known as menstruation.

Q.7 Draw a lebelled diagram of the longitudinal section of a flower.

Q.8 What are the different methods of contraception?

The different methods of contraception are:

1. Barrier method: In this method, the meeting of ovum with sperm is checked with the help of a mechanical barrier. Mechanical barrier such as condoms are made of thin and flexible rubber. The mechanical barrier is available for both males and females. These are used to cover penis in males and vagina in females and prevent sperms from entering the uterus during sexual intercourse to avoid pregnancy.
2. Oral contraceptive: This is method in which hormones are introduced in the female partner to prevent the release of egg to avoid pregnancy. The hormones are taken orally in the form of tablets or pills.
3. Intrauterine devices (IUDs): Contraceptive devices such as the loop or Copper T are placed in the uterus that prevent sperms from reaching the egg and prevent pregnancy to occur.
4. Surgical methods: Transfer of gametes can be blocked by using surgical methods. Surgical method is an irreversible method of contraception. Surgically, in males, vas deferens is blocked to stop the sperm transfer. This process is known as vasectomy. In females, surgically fallopian tubes are blocked to carry the eggs to the uterus. This surgical procedure in females is called tubectomy.

Q.9 How are the modes for reproduction different in unicellular and multicellular organisms?

Unicellular organisms have single cell. Generally, unicellular organisms reproduce by asexual methods like binary fission, multiple fission, budding, etc. For example, Amoeba reproduces by binary fission, yeast reproduces by budding, and Plasmodium reproduces by multiple fission method. Multicellular organisms are made up of either simple cells or complex tissues and organs. Some of their cells are specialised to perform the function of reproduction. Multicellular organisms can employ the asexual methods of reproduction as well as sexual methods of reproduction. Asexual methods include budding, fragmentation, spore formation and vegetative propagation. Complex multicellular organisms possess a well developed reproductive system having specialised reproductive organs.

Q.10 How does reproduction help in providing stability to populations of species?

In an ecosystem, organisms of different species use their ability of reproduction to survive and maintain their populations in their niches.

In an ecosystem, every individual of a species struggle for food, shelter and protection for their survival and existence. Factors like death at the end of natural life cycle, competition, predation, migration and sudden environmental changes keep on reducing population of species on a regular basis. The process of reproduction is the only way to overcome this continuous depletion of individuals from the populations of diverse species. Therefore, reproduction helps in providing stability to populations of species.

Q.11 What could be the reason for adopting contraceptive methods?

Contraceptive methods are mainly adopted because of the following reasons:

1. These devices prevent unwanted pregnancies to occur.
2. These devices not only help in restricting the number of children but also help in maintaining age gap between children. The age gap between children help parents in good bringing up of their children and less number of children ensures the improved living standards of a family.
3. These devices also prevent the spread of sexually transmitted diseases (STDs).
4. These devices play a role in controlling increase in human population and help in reducing pressure on life supporting natural resources such as food, air, water, fuel, etc.