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

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

You will find NCERT Solutions for Class 10 Science Chapter 8 How do Organisms Reproduce on this page through which you can prepare your own answers by taking help from these NCERT Solutions. It will help in developing skills and and helpful in understanding the concepts in better way. Whenever you have any doubts in any question, you can take help from these given Class 10 Science NCERT Solutions.

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

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


In Text Questions

Page No: 128

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

Solution

DNA is a self-replicating material which is present in nearly all living organisms as the main constituent of chromosomes and as a carrier of genetic information. It is an essential part of reproduction because additional copies of DNA made during the process of replication is necessary for the formation of new cells formed after the cell division. Without replication, each cell lacks enough genetic material to provide instructions for creating proteins essential for bodily function.

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

Solution

Variations are differences among individuals produced as a result of errors caused during DNA copying at the time of cell division. Sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult. For example, if the temperature of water increases suddenly, then most of the bacteria living in that water would die. Only few variants that are resistant to heat would be able to survive. However, if these variants were not there, then the entire species of bacteria would have been destroyed. Thus, all variations are not necessarily beneficial for the individual organisms.

Page No: 133

1. How does binary fission differ from multiple fission?

Solution

Binary Fission Multiple Fission
It forms two daughter individuals in which nucleus of the parent body divides only once. It produces a number of daughter individuals in which nucleus of the parent body divides repeatedly.
No protective wall or coat is formed during fission around the cell. A protective wall or a coat is formed around the cell.
Nucleus and cytoplasm divides simultaneously. The nucleus divides into many nuclei first then each nucleus is is surrounded by cytoplasm and daughter cells are released by rupturing of the parent cell.
It occurs under a favourable condition. It occurs under an unfavourable adverse condition.
Examples are Amoeba and Bacteria. Example is Plasmodium.

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

Solution

Advantages of spore formation:
• Spores are thick walled which protect the organism from unfavourable condition and remain dormant till favourable conditions become available.
• Large numbers of spores are produced in one sporangium.
• Spores are distributed easily by air to far-off places to avoid competition at one place.
• Spores are light weighted so they can easily be transfer from one plant to other for germination.

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

Solution

In complex multicellular organisms, specialised cells make up tissues; tissues make up organs; organs make up organ systems, and finally organ systems make up organisms. Since complex multicellular organisms have a very high degree of organisation in their body, they cannot be reproduced from their cut body parts by the process of regeneration.

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

Solution

Vegetative propagation is practiced for growing certain types of plants because:
(i) It is the only method of reproduction in those plants which have lost their capacity to produce seeds like banana, pineapple, orange etc.
(ii) Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds.
(iii) Plants produced by this method are genetically similar enough to the parent plant to have all its characteristics.
(iv) Vegetative propagation is used in methods such as layering or grafting to grow many plants like sugarcane, roses, or grapes for agricultural purposes.

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

Solution

DNA copying is an essential part of reproduction as it passes genetic information from parents to offspring. It also helps to generates variations during sexual reproduction and leads to evolution. This explains how DNA copying is an essential part of the process of replication.

Page No: 140

1. How is the process of pollination different from fertilization?

Solution

Pollination is the transfer of pollen grains from the anther of stamen of a flower to the stigma of a carpel in the same flower or another flower of the same species while fertilisation occurs when the male gamete present in the pollen grain joins with the female gamete present in ovule to form a zygote.

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

Solution

Both the seminal vesicles and the prostate gland add their secretions so that the sperms are in fluid which makes their transportation easier. These secretion also provides nutrient in the form of fructose, calcium, and some enzymes. 

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

Solution

The changes seen in girls at the time of puberty are:
→ Increase in breast size and darkening of skin of the nipples present at the tips of the breasts.
→ Appearance of hair in the genital area.
→ Appearance of hair in other areas of skin like underarms, face, hands, and legs.
→ Increase in the size of uterus and ovary.
→ Beginning of menstrual cycle.
→ More secretion of oil from the skin, which results in the appearance of pimples.

4. How does the embryo get nourishment inside the mother's body?

Solution

The embryo gets nutrition from the mother's blood with the help of a special tissue called placenta . Placenta contains Villi on the embryo’s side of the tissue and blood spaces on mother’s side surrounding the villi. Placenta brings the foetal and maternal blood close enough so they exchange their materials. 

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

Solution

Copper-T can prevent unwanted pregnancy but cannot protect women from acquiring sexually transmitted diseases.

Exercise

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


Solution

(b) yeast.

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


Solution

(c) Vas deferens

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


Solution

(d) pollen grains.

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

Solution

The advantages of sexual reproduction over asexual reproduction are:
(i) Variation: In sexual reproduction, male and female gametes combines to give rise to variation which ensures survival of species in a population.
(ii) Evolution: The new formed individual has characteristics of both the parents which results in the formation of better varieties.

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

Solution

The functions performed by the testis in human beings:
(i) It helps in the production of haploid and motile male gametes called sperms which takes part in sexual reproduction.
(ii) It assists in the secretion of the testosterone hormone, which plays a key role in the development of secondary sexual characters in male.

6. Why does menstruation occur?

Solution

Menstruation is normal vaginal bleeding that occurs as part of a woman's monthly cycle. Every month, one egg is released by an ovary and if the egg is not fertilised, it lives for about one day. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilised egg. If the egg does not get fertilised, then the lining of the uterus breaks down slowly and gets released in the form of blood and mucous from the vagina.

7. Draw a labelled diagram of the longitudinal section of a flower.

Solution

diagram of the longitudinal section of a flower

8. What are the different methods of contraception?

Solution

(i) Barrier Method: It is a method that actually creates barriers for the sperm and prevents it from reaching the egg. Example is Condom.
(ii) Oral contraceptives: In this method, pills or drugs are taken orally which contain small doses of hormones that prevent the release of eggs and thus fertilization cannot occur.
(iii) Surgical method: This method is applicable to both male and female. If the vas deferens in the male is blocked, sperm transfer will be prevented (vasectomy). If the fallopian tube in the female is blocked, the egg will not be able to reach the uterus (tubectomy). In both cases fertilisation will not take place. Surgical methods can be used to create such blocks.
(iv) Intrauterine devices (IUDs): It is T-shaped device which is placed inside the uterus. It blocks the sperms to enter into the fallopian tube. e.g., Copper-T is placed in the uterus to prevent pregnancy.

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

Solution

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

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

Solution

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.

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

Solution

(i) These methods prevent pregnancy in women.
(ii) These methods also prevent transmission of sexually transmitted diseases.

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