Class Ten Science NCERT Solutions Chapter 8

Chapter 8: How Do Organisms Reproduce?

Text Book Exercises

Q.13. Asexual reproduction takes place through budding in :

(a) Amoeba (b) Yeast

(c) Plasmodium (d) Leishmania

Ans. (b) Yeast

Q.14. Which of the following is not a part of the female reproductive system in human beings?

(a) Ovary (b) Uterus

(c) Vas deferens (d) Fallopian tube.

Ans. (c) Vas deferens.

Q.15. The anther contains

(a) sepals (b) ovules

(c) carpel (d) pollen grains.

Ans. (d) Pollen grains.

Q.16. What are the advantages of sexual reproduction over asexual reproduction?

Ans. Sexual reproduction leads to variations due to the recombination of genetic material during DNA copying or cell division. These variations are essential for the survival of species. On the contrary, asexual reproduction does not bring about variations.

Q.17. What are the functions performed by the testis in human beings?

Ans. Functions of testes

(i) Produce sperms, which contain a haploid set of chromosomes from father.

(ii) Produce a hormone called testosterone, which brings about secondary sexual characters in boys.

Q.18. Why does menstruation occur?

Ans. In the human female, if the egg is not fertilised, it lives for about one day. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilised egg. Thus, its lining becomes thick and spongy. This would be required for nourishing the embryo if it had fertilised. However, this lining is not required any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle takes place every 28 days and is known as menstruation.

Q. 20. What are the different methods of contraception?

Ans. The contraceptive methods can be broadly divided into the following types :

(i) Natural method: It involves avoiding the chances of the meeting of sperms and ovum. In this method, the sexual act is avoided from day 10 to 17th of the menstrual cycle because, during this period, ovulation is expected and therefore, the chances of fertilisation are very high.

(ii) Barrier method: In this method, the fertilisation of ovum and sperm is prevented with the help of barriers. Barriers are available for both males and females. Condoms are bar­riers made of thin rubber that are used to cover penis in males and vagina in females.

(iii) Oral contraceptives: In this method, tablets or drugs are taken orally. These contain small doses of hormones that prevent the release of eggs and thus fertilisation cannot occur.

(iv) Implants and surgical methods: Contraceptive devices such as the loop or Copper-T are placed in the uterus to prevent pregnancy. Some surgical methods can also be used to block the gamete transfer. It includes the blocking of vas deferens to prevent the transfer of sperms known as vasectomy. Similarly, fallopian tubes of the female can be blocked so that the egg will not reach the uterus known as tubectomy.

Q.21. How are the modes of reproduction different in unicellular and multicellular organisms?

Ans. In unicellular organisms, reproduction occurs by the division of the entire cell. The modes of reproduction in unicellular organisms can be fission, budding, etc. whereas, in multicellular organisms, specialised reproductive organs are present. Therefore, they can reproduce by complex reproductive methods such as vegetative propagation, spore formation, etc. In more complex multicellular organisms such as human beings and plants, the mode of reproduction is sexual reproduction.

Q. 22. How does reproduction help in providing stability to populations of species?

Ans. Reproduction is the process of producing new individuals of the same species by existing organisms of a species, so it helps in providing stability to the population of species by giving birth to new individuals as the rate of birth must be at par with the rate of death to provide stability to the population of a species.

Q. 23. What could be the reasons for adopting contraceptive methods?

Ans. The sexual act always has the potential to lead to pregnancy. Pregnancy will make major demands on the body and the mind of the woman and if she is not ready for it, her health will adversely be affected. Therefore, adopted contraceptive methods are essential. Some contraceptive methods like condom also prevent the spread of STDs and lethal diseases like HIV-AIDS.