NCERT In Text Questions and Solutions: Chapter 8 - How do Organisms reproduce?, Class 10, Science PDF Download

Class Ten Science CBSE

How Do Organisms Reproduce?

NCERT Book - In Text Questions and Solutions

1. What is the importance of DNA copying in reproduction?

Answer: DNA copying is important for reproduction. Additional copies of DNA are made during replication; which is necessary for the new cells formed after cell division. Moreover, some minor alterations during DNA replication are responsible for bringing variations in the long run.

2. Why is variation beneficial to the species but not necessarily for the individual?

Answer: A variation may be beneficial to the species but not necessarily for the individual. This can be understood with the following hypothetical example. Let us recall how giraffe may have evolved from their ancestors who had shorter necks. A giraffe had had to crane its neck longer to reach the uppermost branches. For most of the individual giraffe, it must have been a painful experience. But in the long run, those who could succeed in reaching the uppermost branches survived and others perished. So, developing a longer neck had no foreseeable short term gains but it was beneficial for the species.

3. How does binary fission differ from multiple fission?

Answer:

4. How will an organism be benefited if it reproduces through spores?

Answer: Reproduction through spores gives several advantages to an organism. Some of them are as follows:

1. Spores can remain dormant till favourable conditions become available.
2. Spores help an organism to tide over the bad phase.
3. Spores can be spread through water, air or animals and thus is good for the spread of an organism to more places.

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

Answer: Regeneration happens through mitosis and a particular type of tissue can give rise to its own kind only. In complex organisms, different tissues and organs have altogether different structures. Regenerating a different kind of tissue from another kind is not possible. Hence, complex organisms are unable to give rise to new individuals through regeneration.

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

Answer: Vegetative propagation has some inherent advantages. It takes less time to grow a plant through vegetative propagation. Different traits of a species can be developed on the same plant through this process. Many plants grown through vegetative propagation take less time to give fruits and other beneficial plant produce. These are the reason, vegetative propagation is practiced for growing some types of plants.

7. Why is DNA copying an essential part of the process of reproduction?

Answer: DNAs are the carriers of genetic information. For an organism to produce its own kind, it becomes necessary that the offspring get similar DNAs as in parents. DNA replication is the way through which a cell makes additional copies of DNA so that they can be transferred to the offspring. This explains how DNA copying is an essential part of the process of replication.

8. How is the process of pollination different from fertilisation?

Answer: Transfer of pollen grains from anther to stigma is called pollination. On the other hand, fusion of male and female gametes is called fertilization. Pollination is a physical process in which movement of pollen grains are attained by certain physical factors. Fertilization is a biological process. Ovary is the site of fertilization and embryo is the product of fertilization.

9. What is the role of the seminal vesicles and the prostate gland?

Answer: Prostate gland: Makes the medium of semen alkaline.

Seminal vesicle: Adds fluid content to the semen.

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

Answer: At the time of puberty, secondary sexual characters develop and sexual maturity takes place. This is manifested by many changes in both girls and boys. Some of the changes seen in girls at the time of puberty are as follows:

• Voice becomes thin.
• Breasts enlarge.
• Hips become rounded.
• Hairs grow under the armpit and in pubic area.
• Menstruation begins.