NCERT Solutions for Class 10th Science
Chapter 8 – HOW DO ORGANISMS REPRODUCE
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.1 What is the importance of DNA copying in reproduction?
Ans Reproduction ensures the continuation of similar kinds of individuals, generation after generation i.e. it involves making copies of the blueprints of body design. These features (blueprints of body design) are inherited from parents to next generation in the form of DNA (Deoxyribo Nucleic Acid). Further copying the DNA will have some variations each time due to which the surviving cells are similar to, but subtly different from each other. This inbuilt tendency for variation during reproduction is the basis for evolution. Hence DNA copying is important in reproduction as through this the organisms pass on their body features to their offspring.
Q.2 Why is variation beneficial to the species but not necessarily for the individual?
Ans Variation happens because of the occurrence of errors during the process of DNA copying at the time of cell division. Populations of organisms fill well-defined places, or niches, in the ecosystem, using their ability to reproduce. If a population of reproducing organisms were suited to a particular niche and if the niche were drastically altered, the population could be wiped out. However, if some variations suitable for changed environment were to be present in a few individuals in these populations, there would be some chance for them to survive. The surviving individuals may reproduce and develop a population suitable to the changed niche. Thus, variation is beneficial to the species (for the survival of species over time) but not necessarily for the individual.
Q.3 How does binary fission differ from multiple fission?
Q.4 How will an organism be benefited if it reproduces through spores?
Q.5 Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Q.6 Why is vegetative propagation practised for growing some types of plants?
Ans Vegetative propagation is practised for growing some types of plants because:
1) Plants which have lost the capacity to produce seeds like banana, orange etc. can also be grown.
2) Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds.
3) Plants produced from seeds show variation whereas plants raised by vegetative propagation are genetically similar to the parent plant and gives desired quality product.
Q.7 Why is DNA copying an essential part of the process of reproduction?
Q.8 How is the process of pollination different from fertilisation?
Q.9 What is the role of the seminal vesicles and the prostate gland?
Q.10 What are the changes seen in girls at the time of puberty?
Q.11 How does the embryo get nourishment inside the mother’s body?
Q.12 If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?
Ans No, using a copper-T will not help help in protecting her from sexually transmitted diseases. Copper-T is just a contraceptive device which is placed in the uterus to prevent pregnancy and does not protect against sexually transmitted diseases (bacterial or viral infections).
EXERCISES
Q.1 Asexual reproduction takes place through budding in
(a) amoeba.
(b) yeast.
(c) plasmodium.
(d) leishmania.
Ans (b) yeast.
Q.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
Ans (c) Vas deferens.
The female reproductive system in human beings consists of ovaries, fallopian tubes, uterus and vagina. Vas deferens is a part of male reproductive system in human beings.
Q.3 The anther contains
(a) sepals.
(b) ovules.
(c) carpel.
(d) pollen grains.
Ans (d) pollen grains.
Q.4 What are the advantages of sexual reproduction over asexual reproduction?
Ans Advantages of sexual reproduction over asexual reproduction:
1) Sexual reproduction involves fusion of gametes coming from two different individuals and thus promotes the diversity of characters in the offsprings.
2) Sexual reproduction involves DNA copying mechanism that creates variations which are useful for ensuring the survival of the species. This genetic variation results in the origin of new
Q.5 What are the functions performed by the testis in human beings?
Q.6 Why does menstruation occur?
Q.7 Draw a labelled diagram of the longitudinal section of a flower.
Q.8 What are the different methods of contraception?
Ans Different methods of contraception are:
1) Mechanical Barrier: In this method a barrier is used so that sperm does not reach the egg. Devices such as condoms, diaphragms and cervical caps are used.
2) Hormonal Method: In this method hormonal balance of the body is made to change so that eggs are not released and fertilisation cannot occur. These drugs commonly need to be taken orally as pills.
3) Intrauterine Contraceptive Devices (IUCD): In this method contraceptive devices are placed in the uterus to prevent pregnancy. Commonly used IUCDs are Loop and Copper-T.
4) Surgical Methods: The surgical methods are
a) Vasectomy – In this method, vas deferens in the male is blocked (by cutting and tying) and thus preventing sperm from reaching semen from testes.
b) Tubectomy – In this method, fallopian tube in the female is blocked (by cutting and tying) and thus preventing the egg from reaching uterus.
Q.9 How are the modes for reproduction different in unicellular and multicellular organisms?
Q.10 How does reproduction help in providing stability to populations of species?
Q.11 What could be the reasons for adopting contraceptive methods?