CLASS 10 SCIENCE NCERT SOLUTION FOR CHAPTER – 8 How do Organisms Reproduce

How do Organisms Reproduce

NCERT Questions

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

Answer.
DNA or deoxy ribonucleic acid is the genetic material present in the chromosomes. It is responsible for the body design of an organism. Hence, DNA copying is very important for reproduction. During reproduction, additional copies of DNA are made so that each new daughter cell formed has its own DNA.

However, during DNA copying, some minor alterations occur. This results in bringing variations in the long run.

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

Answer.
Organisms are normally adapted to live in a particular kind of niche. In case of alteration in the ecological condition of that niche, the organism would not be able to survive. Only the variants of the organisms resistant to changes would survive and grow further. Thus, variation is beneficial but not necessarily for the individual.

Question 3.
Why is DNA copying an essential part of the process of reproduction?

Answer.
DNA copying is essential for inheritance of features from parents to the next generation.

Question 4.
Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

Answer.
(a) The body of complex organisms consist of several organ systems which perform
specific functions.
(b) Regeneration is carried out by specialised cells which are not present in complex organisms.

Question 5.
How does binary fission differ from multiple fission?

Answer.

Binary fissionMultiple fission
1. In this process of reproduction, the cytoplasm of a parent cell divides equally along with the division of nucleus to form two daughter cells.1. In this process of reproduction, many daughter cells are formed by the division of a parent cell. 
2. Amoeba and bacteria divide by this process.2. Plasmodium divides by this process. 

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

Answer.
Vegetative propagation is the only method of reproduction of such plants which do not form viable seeds. It allows the plant to grow quickly. It takes less time to produce fruits or other beneficial plant produce.

Question 7.
How is the process of pollination different from fertilisation?

Answer.
Pollination is the physical process of transfer of pollen grains from anther to the stigma of the same flower or another flower of the same species whereas fertilisation is a biological process in which fusion of male and female gametes takes place.

Question 8.
What is the role of the seminal vesicles and the prostate gland?

Answer.
The prostate gland makes the medium of semen alkaline as sperms require an alkaline medium to thrive. The seminal vesicle adds fluid content to the semen.

Question 9.
What are the changes seen in girls at the time of puberty?

Answer.
Some of the changes seen in girls at the time of puberty are:

  1.  The breasts enlarge in size.
  2.  The hips accumulate fat.
  3.  Hairs’grow in the armpits and pubic area.
  4.  The voice becomes thin.
  5.  Girls begin to menstruate.

Question 10.
How does the embryo get nourishment inside the mother’s body?

Answer.
The embryo gets nourishment through placenta. It is a cluster of tissues embedded in the uterine wall of the mother’s body.

Question 11.
If a woman is using a copper-T, will it help in protecting her from sexually transmitted disease?

Answer.
No, because the copper-T just hampers the process of implantation of embryo in the uterine wall but not provides protection against sexually transmitted diseases.

Question 12.
How will an organism be benefited if it reproduces through spores?

Answer.
There are several advantages if the organism reproduces by spares:

  1.  There are large numbers of spores formed from one sporangium.
  2.  The spores can remain in dormant state till the favourable conditions are available.
  3.  The spores have thick covering called cyst which helps them to survive in unfavourable conditions.
  4.  The spores are very light and can spread easily through water, air or through the animals.

Chapter End Questions

Question 1.
Asexual reproduction takes place through budding in
(a)
 amoeba
(b) yeast
(c) plasmodium
(d) leishmania

Answer.
(b) yeast

Question 2.
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

Answer.
(c) Vas deferens

Question 3.
The anthers contains
(a)
 sepals
(b) ovules
(c) carpel
(d) pollen grains

Answer.
(d) pollen grains

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

Answer.
(a) Sexual reproduction provides opportunity – for new recombination of genes thus causes genetic variations, which is not applicable to asexual reproduction.
(b) Sexual reproduction plays an important role in evolution of new species but the asexual reproduction does not.

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

Answer.
(a) They form sperms from the germinal cells present in the seminiferous tubules.
(b) The hormone testosterone secreted by the Leydig cells induces secondary sexual characters in male.

Question 6.
Why does menstruation occur?

Answer.
In every month as one of the ovaries releases ovum and tfie uterine wall thickens and prepares itself for receiving the developing zygote. When the egg is not fertilised, the level of progesterone starts decreasing, due to which nourishment to the endometrium is stopped.

As a result, the lining of uterine wall slowly breaks and the discharge of unfertilised egg along with ruptured endometrium and mucus causes menstruation in a human female.

Question 7.
Draw a labeled diagram of the longitudinal section of a flower.

Answer.

NCERT Solutions for Class 10 Science Chapter 8 How do Organisms Reproduce 1

Question 8.
What are the different methods of contraception?

Answer.

Methods of Contraception

  1.  Barrier Methods: Physical devices which prevent the entry of sperms into the female reproductive tract come under barrier methods. Condoms, diaphragms and cervical caps can be used as barrier method.
  2.  Chemical Methods: In these methods, specific drugs are used by the females to avoid pregnancy. These drugs change the hormonal balance of the body so that eggs are not released and fertilisation does not occur. These drugs are taken orally as pills, and therefore, called Oral Contraceptives (OCs).
  3.  IUCDs (Intra Uterine Contraceptive Devices): Lippe’s loop or copper-T are contraceptive devices which are placed inside the uterus to prevent implantation of the embryo.
  4.  Surgical Methods: Vasectomy in males and tubectomy in females are surgical methods of population control.
    1.  In males, a small portion of the vas deferens is surgically removed and then cut-ends are tied to prevent the transfer of sperm. This is called vasectomy.
    2.  In females, a small portion of the fallopian tube is surgically removed and the cut-ends are tied to prevent the passage of egg in the uterus. This is called tubectomy.

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

Answer.
The unicellular organisms reproduce generally by asexual reproduction like budding, binary and multiple fission. However, some unicellular forms also exhibit primitive types of sexual reproduction like conjugation found in some types of bacteria.

The multicellular organisms have a complex body structure and reproduce sexually by the distinct sexual body parts. However, some lower multicellular organisms such as hydra reproduces sexually in poor feeding conditions.

Question 10.
How does reproduction help in providing stability to population of species?

Answer.
Every species has to struggle for its existence. A large number of the population of a particular species is removed by the predators or by the unfavorable environmental conditions. Reproduction is the only way to replenish the lost section of the population. If the organisms of species do not reproduce, their species will foil to exist.

Question 11.
What could be the reasons for adopting contraceptive methods?

Answer.
Contraceptive methods are adopted to:
(a) prevent unwanted conception
(b) have sufficient gap between the successive births.

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