CBSE Class 10 Science
Ch-8 How Do Organisms Reproduce?
NCERT Solutions for Class 10th Science Chapter 8 How Do Organisms Reproduce?
Question 1. What is the importance of DNA copying in reproduction?
Answer: DNA copying in reproduction is important for maintenance of body designs and features. Moreover, DNA copying leads to variations. Variation is useful for the survival of species.
Question 2. Why is variation beneficial to the species but not necessarily for the individual?
Answer: Population of organisms reside in well-defined places or niches in the ecosystem. However, niches can change because of reasons beyond the control of the organisms, e.g., temperature changes, water level changes, etc. If population of reproducing organisms suited to particular niche and if the niche is drastically altered, the population can be wiped out. However, if some variations are present in a few inAividuals in these populations, there will be chances for their survival. The surviving individual can further reproduce and develop a population according to the changed niche, Thus, variation is beneficial to the species but not necessarily for the individual.
Question 1. How does binary fission differ from multiple fission ?
Answer: When two new daughter cells are formed as a result of fission. It is called binary fission, e.g., Amoeba.When many daughter cells are formed as a result of fission, this is called multiple fission, e.g., Malarial parasite.
Question 2. How will an organism be benefited if it reproduces through spores?
Answer: Spore formation is an asexual mode of reproduction. Spores formed are covered by
thick walls that protect them from adverse conditions. During favourable condition thick resistant wall breaks down and new organism grows from it.
Spores are very light weight and they easily get dispersed through winds which give them more variations and thus better chances of survival.
Question 3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer: Complex organisms are not simply a random collection of cells where sPecialized cells are
organised as tissues, and tissues ale organised into organs which then have to be placed at definite
positions in the body. In such a carefully organised situation, it is not easy to develoP organism
Question 4. Why is vegetative propagation practised for growing some type of plants?
Answer: Vegetative propagation makes possible for the propagation of plants such as banana, orange, rose and jasmine that have lo6t the capacity to Produce seeds. Moreover, all plants produced through vegetative propagation are genetically similar to the parent plant.
Question 5. Why is DNA copying an essential part of the process of reproduction?
Answer: The process of reproduction results in the production of off springs which resemble to their parents. This means during the reproduction there must be a transfer of the blueprint of the body design from parent to the off springs. As we know DNA contains all the information that passes from parents to the next generation, so before reproduction, DNA is copied in the parent cell. Out of these two copies, one copy is passed to the newly formed individual.
Question 1. How is the process Of pollination different from fertilization ?
Answer: Pollination is the transfer of pollen grains from the anther to the stigma Of a flower whereas fertilization is the fusion Of male gamete with female gamete (egg).
Question 2. What is the role of the seminal vesicles and the prostate gland ?
Answer: Seminal vesicles and the prostate gland add their secretions so that the sperms are in a fluid (semen) which makes their transport easier and this fluid also provides nutrition.
Question 3. What are the changes seen in girls at the time Of puberty ?
Answer: Changes seen in girls at the time of puberty are :
1. Breast size begins to increase.
2. Girls begin to menstruate.
3.Growth Of pubic hair.
4.Skin becomes oily.
Question 4. How does the embryo get nourishment inside the Mother’s body?
Answer: embryo gets nutrition from mother’s blood with the help Of a special tissue called placenta. Through placenta, glucose and oxygen pass from mother to the embryo. Moreover, waste substance of embryo are removed through placenta into the
Question 5. If a woman is using a copper-T will it help in protecting her from sexually transmitted diseases?
Answer: No, copper-Twill not protect her from Only Barrier methods protect from sexually transmitted diseases.
Question 1. Asexual reproduction takes place through budding in :
Answer: (b) Yeast.
Question 2. Which of the following is not a pan Of the female reproductive system in human beings ?
(c) Vas deferens
(d) Fallopian tube
Answer: (c) Vas deferens.
Question 3. The anther contains :
(d) Pollen grains.
Answer: (d) Pollen grains
Question 4. What are the advantages of sexual reproduction over asexual reproduction?
Answer: Sexual reproduction leads to new combination Of genes as it involves two parents and meiosis. This produces variation in offspring. Variations are the basis for evolution.
Question 5. What are the functions performed by the testes in human beings?
Answer: Functions Of testes are .
(i) Testes produce sperms.
(ii) Testosterone (male sex hormone) is also produced by testes.
Question 6. Why does menstruation occur?
Answer: If the egg is not fertilized and uterus does not get zygote, the developed lining slowly breaks and menstruation occur.
Question 8. What are the different methods of contraception?
Answer: There are three main methods of contraception :
- Barrier methods,
- Chemical methods, and
- Surgical methods.
1. Barrier methods: In barrier methods, physical devices such as condom, diaphragm and cervical caps are used. They prevent the entry Of sperms in the female genital tract during copulation.
2. Chemical methods: The chemical methods make use of specific drugs by females. There are two types of such drugs, Oral pills and vaginal pills. Oral pills are mainly hormonal preparation, and are called oral contraceptives (OCS).
3. Surgical methods: In the surgical methods, a small portion of vas deferens in male, and the fallopian tube in female, in surgically removed or ligated (tied). It is called vasectomy in males and tubectomy in females.
Apart from these three methods the intrauterine contraceptive devices are used to prevent pregnancies. The use of Intra Uterine Contraceptive Devices (IUCDs) is also very effective and popular. A copper-T is placed safely inside the uterus by a practising doctor or a skilled nurse. IUCDs prevent implantation in the uterus.
Question 9. How are the modes for reproduction different in unicellular and multicellular organisms ?
Answer: Unicellular organisms reproduce asexually whereas multicellular organisms reproduce manly by n 1 reproduction.
Question 10. How does reproduction help in providing stability to populations Of species?
Answer: The rate Of birth and death in a given population determine its stability. The rate of birth should be approximately equal to the rate of death. So, by checking birth rate, which is increasing at an alarming rate, stability to population of species can be provided
Question 11. What could be the reasons for adopting contraceptive methods?
Answer: Frequent pregnancies have an adverse effect on the health of a woman. Frequent and unwanted pregnancies can be avoided by adopting contraceptive methods. Also, these methods check population growth by controlling child birth rate.