NCERT Solutions for Class 10 Science Chapter 7 - How Do Organisms Reproduce?

Question 1:

What is the importance of DNA copying in reproduction?


Organisms look similar because their body designs are similar. If body designs are to be similar, the blueprints for these designs should also be similar. Thus, DNA copying during reproduction involves making copies of the blueprints of body design.

Question 2:

Why is variation beneficial to the species but not necessarily for the individuals?


The DNA copies generated in reproducing cells are similar but may not be exactly identical to the original. Thus, the cells will be subtly different from each other. This inbuilt tendency for variation to occur during reproduction is the main cause of formation of new species. Hence, variations are beneficial to the species but not necessarily for the individual.

Question 3:

How does binary fission differ from multiple fission?



Question 4:

How will an organism be benefited if it reproduces by spores?


The spores are covered with thick walls that protect them until they come into contact with another moist surface and begin to grow. Thus, it is beneficial for the organisms such as Rhizopus to reproduce through spores.

Question 5:

Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?


More complex organisms have a very high degree of organization in their body, that is, specialized cells make up tissues, tissues make up organs, organs make up organ systems and organ systems make up organisms. Hence, they cannot be reproduced from their cut body parts by the process of regeneration. Organisms such as Hydra, Planaria can reproduce through regeneration as they have relatively simple body organization consisting of only a few specialized cells.

Question 6:

Why is vegetative propagation practised for growing some types of plants?


(a) Vegetative propagation is a means of propagating such plants which do not produce viable seeds.
(b) It is a rapid method of producing young ones.
(c) It helps in retaining useful characters from generation to generation.

Question 7:

Why is DNA copying essential part of the process of reproduction?


(a) DNA copying provides cellular apparatus in the daughter cells. (b) DNA in daughter cells will be able to control the functioning of daughter cells. (c) DNA copies will retain the traits.

Question 8:

How is process of pollination different from fertilisation?


Pollination is the process in which pollen grains are transferred from anther to the stigma of a flower. Fertilisation is the process in which fusion of male gamete with female gamete takes place to form zygote.

Question 9:

What is the role of seminal vesicles and prostate gland?


Seminal vesicles secrete a viscous secretion containing fructose and prostaglandins. The fructose is source of energy for sperm and prostaglandins stimulate uterine contraction and thus help the sperm to move towards the female’s oviduct.

Prostate gland secretes an alkaline and milky fluid that aids in sperm motility. The fluid contains small amount of citric acid, some lipids and a few enzymes. It also contains bicarbonate ions which makes the semen alkaline.

Question 10:

What are the changes seen in girls at the time of puberty?


The following changes are seen in girls at the time of puberty:
(a) Growth of breast and external genitalia. (b) Darkening of nipple skin.
(c) Broadening of pelvis. (d) Growth of pubic and axillary hair.
(e) Increase in subcutaneous fat. (f ) Initiation of menstruation and ovulation. Changes at puberty occur under the influence of FSH (Follicle stimulating hormone) and estrogen hormone.

Question 11:

How does embryo get nourishment inside the mother’s body?


Embryo gets nourishment through placenta inside the mother’s body. Placenta is a disc-like special tissue embedded in the wall of uterus. It contains villi on the embryo side of tissue. On the mother side are blood spaces which surround villi. Placenta brings the foetal and maternal blood close enough to permit exchange of materials between the two.

Question 12:

If a woman is using a copper-T, will it help her in protecting sexually transmitted diseases?


Copper-T can prevent unwanted pregnancy but cannot protect women from acquiring sexually transmitted diseases (if her partner has such a disease).

Question 13:

Asexual reproduction takes place through budding in:

  1. Amoeba
  2. Yeast
  3. Plasmodium
  4. Leishmania

(b) Yeast

Question 14:

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

(c) Vas deferens

Question 15:

The anther contains:

  1. Sepals
  2. Ovules
  3. Pistil
  4. Pollen grains

(d) Pollen grains

Question 16:

What are the advantages of sexual reproduction over asexual reproduction?


The advantages of sexual reproduction over asexual reproduction are:
(a) Sexual reproduction introduces variations in offspring, hence it is of evolutionary significance.
(b) As a result of new character combination, better offspring are produced which results in the formation of better varieties.

Question 17:

What are the functions performed by the testis in human beings?


The following functions are performed by the testis in human beings:
(a) Testis produce haploid and motile male gametes called sperms.
(b) Leydig’s cells which lie scattered in interstitial spaces between seminiferous tubules secrete male sex hormone called testosterone which controls the development of secondary sexual characters in males.

Question 18:

Why does menstruation occur?


If a sperm is not available at the time of ovulation, then fertilization of ovum does not take place. As a result, the thick and soft uterus lining having a lot of blood capillaries in it is not required. The unfertilized ovum dies within a day and the uterus lining also breaks down. Since the thick and soft uterus lining contains a lot of blood vessels, the breaking of the uterus lining produces blood alongwith other tissues. The blood comes and other tissues come out of the vagina in the form of menstrual flow.

Question 19:

Draw a labelled diagram of longitudinal section of flower.



Question 20:

What are different methods of contraception?



Question 21:

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


Unicellular organisms mostly reproduce by asexual reproduction. The multicellular organisms reproduce mostly by sexual reproduction.

Question 22:

How does reproduction help in providing stability to population of species?


Reproduction gives rise to more organisms with the same basic characteristics as their parents. If however, some species of the living organism cannot reproduce due to certain reasons, then the organisms of this species will gradually die out and disappear from the earth. Hence, reproduction is the only method which helps in providing stability to population of species.

Question 23:

What could be the reasons for adopting contraceptive methods?


Some of the reasons for adopting contraceptive methods are:
(a) These methods prevent pregnancy in women.
(b) These methods also prevent transmission of sexually transmitted diseases.