NCERT Solutions Class 10 Science
The NCERT Solutions in English Language for Class 10 Science Chapter – 8 (How do Organisms Reproduce?) has been provided here to help the students in solving the questions from this exercise.
Chapter – 8 (How do Organisms Reproduce?)
Questions
1. What is the importance of DNA copying in reproduction ?
Answer – DNA – Deoxyribonucleic acid is the genetic material that is present in the cells of all organisms. DNA carries genetic information from one generation to the other, and this helps in producing organisms of its own types. DNA copying is a must for inheriting the traits from parents. Any variations in DNA copying will give rise to origin of new species.
2. Why are variations beneficial to the species but not necessarily for the individual ?
Answer – Variations are useful for the survival of species in changed environment situations. If a population of reproducing organism were suited to a particular niche and if the niche is drastically altered the population could be wiped out. However, some variations are present some species will survive. Thus, variation is useful to species but not the individual.
Questions
1. How does binary fission differ from multiple fission ?
Answer –
| Binary Fission | Multiple Fission |
| 1. Products. It gives rise to two individuals. | 1. It forms several (more than two) individuals. |
| 2. Conditions. Binary fission occurs under favourable conditions. | 2. Multiple fission occurs both under favourable and unfavourable conditions. |
| 3. Nucleus. Nucleus of the parent cell divides only once to form two daughters. | 3. Nucleus of the parent undergoes repeated divisions to form a number of daughter nuclei. |
| 4. Cytoplasm. Cytoplasm undergoes cleavage after each nuclear division. | 4. Cytoplasm does not divide after every nuclear division. |
| 5. Residue. No part of the parent body is left unused. | 5. A part of the body, covering and residual cytoplasm, is left behind. |
| Examples. Amoeba, Paramecium. | Examples. Plasmodium, Amoeba (encysted). |
2. How will an organism be benefited if it reproduces through spores ?
Answer – Following are the ways through which an organism will be benefited if it reproduces through spores:
- Number of spores produced in one sporangium would be large.
- In order to avoid competition at one place, spores can be distributed to faraway places with the help of air.
- In order to prevent dehydration under unfavorable conditions, the spores are covered by thick walls.
3. Can you think of reasons why more complex organism cannot give rise to new individuals through regeneration.
Answer – Organisms at higher complex levels cannot give rise to new individuals through regeneration because they have organization of their organs system at different levels. All these organ systems are interconnected and work in full coordination. They can regenerate a few of their lost body parts like skin, blood, muscles, etc. but can’t give rise to new individuals.
4. Why is vegetative propagation practised for growing some types of plants?
Answer – Vegetative propagation method is used for growing certain plants which do not produce viable seeds. It is also used for growing of plants bearing superior traits, because they produce genetically identical plants. It is also used for growing plants which require longer time to grow and become mature. Plant which require lot of care during early stages of development are also grown by this method.
5. Why is DNA copying an essential part of the process of reproduction ?
Answer – DNA contains information for the inheritance of features from parents to next generation. DNA presents in nucleus of cells are the information source for making protein. If information is different, different protein will be made that lead to altered body design.
Questions
1. How is the process of pollination different from fertilization?
Answer – Distinction between pollination and fertilisation:
| Pollination | Pollination |
| 1. Definition: It is transfer of pollen grains from anther to the stigma of a flower. | 1. It is the fusion of male and female gametes. |
| 2. Step: Pollination precedes fertilization. | 2. Fertilization occurs only after pollination when the pollen grain has germinated and male gametes are carried into ovule. |
| 3. Purpose: It carries the male gamete producing pollen grains to the female sex organ. | 3. It actually brings about fusion of gametes. |
| 4. Process: Pollination is a physical process. | 4. Fertilization is a physico-chemical (biological) process |
| 5. Occurrence: It occurs only in seed plants. | 5. It occurs in both plants and animals of various types. |
2. What is the role of seminal vesicles and the prostate gland ?
Answer – Secretions of seminal vesicles and prostate gland provide fluid medium to sperm to move and also provide nutrition to them.
3. What are the changes seen in girls at the time of puberty ?
Answer – During puberty breast size begins to increase with darkening of the skin of the nipples at the tip of breasts. Also, girls begin to menstruate at around this time.
4. How does the embryo get nourishment inside the mother’s body ?
Answer – Embryo gets nourishment from mother’s body with the help of placenta through a cord called umbilical cord. Placenta contains many finger-like villi from the chorion covering of the embryo. They occur in contact with blood sinuses of the mother present in the endometrial lining of uterus. All nutrients (glucose, amino acids, vitamins, etc.) diffuse from mother’s blood into villi and from there to embryo through the umbilical cord.
5. If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases ?
Answer – No, sexually transmitted diseases occur due to fluid to fluid contact that takes place in the vagina.
Exercises
1. Asexual reproduction takes place through budding in
(a) Amoeba
(b) Yeast
(c) Plasmodium
(d) Leishmania.
Answer – (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.
Answer – (c) Vas deferens
3. The anther contains
(a) Sepals
(b) Ovules
(c) Carpel
(d) Pollen grains.
Answer – (d) Pollen grains.
4. What are the advantages of sexual reproduction over asexual reproduction ?
Answer – Asexual reproduction is monoparental, with no gametes, no meiosis and very little variations. Sexual reproduction is generally biparental involving fusion of gametes, meiosis and lot of variations.
5. What are the functions performed by testis in human beings ?
Answer – The testes are the male reproductive organs that are located outside the abdominal cavity within a pouch called scrotum.
Functions of testes:
- Produce sperms
- Produce a hormone called testosterone, which brings about secondary sexual characters in boys.
6. Why does menstruation occur ?
Answer – Menstruation occurs in response to low level of estrogen and progesterone hormones which causes constriction of blood vessels in uterine wall, stoppage of nourishment to overgrown endometrium that sloughs off, passing out broken mucosal membrane, blood and mucus.
7. Draw a labelled diagram of L.S. flower.
Answer –
8. What are the different methods of contraception ?
Answer –
- Mechanical Barriers like condoms, cervical cap, diaphragm.
- Oral Contraceptives or oral pills like Mala D, Saheli
- Intrauterine Contraceptive Devices (IUCD) like loop, bow, Cu-T.
- Surgical Methods like vasectomy in males and tubectomy in females.
9. How are the modes for reproduction different in unicellular and multicellular organisms ?
Answer –
| Unicellular Organisms | Multicellular Organisms |
| 1. Reproductive Cell. The same cell which functions as the body of the organism also gets transformed into reproductive cell. | 1. Specific cells take part in reproduction. |
| 2. Technique. Techniques of reproduction are simple. | 2. Techniques of reproduction are commonly complex. |
| 3. Asexual Reproduction. It occurs through fission, budding and spore formation. | 3. It occurs by several methods like fragmentation, regeneration, budding, spore formation, vegetative reproduction, etc. |
| 4. Sex Organs. No special sex cell or sex organ is present. | 4. They are present. |
| 5. Sexual Reproduction. It occurs through isogamy to heterogamy. | 5. It is commonly oogamous. |
10. How does reproduction help in providing stability to population of species ?
Answer – Living organisms reproduce for the continuation of a particular species. It helps in providing stability to the population of species by producing a new individual that resembles the parents. This is the reason why cats give birth to only cats or dogs give birth to only dogs. Therefore, reproduction provides stability to populations of dogs or cats or any other species.
11. What could be the reasons for adopting contraceptive methods ?
Answer – Contraceptive methods are mainly adopted because of the following reasons:
(i) To prevent unwanted pregnancies.
(ii) To control population rise or birth rate.
(iii) To prevent the transfer of sexually transmitted diseases.
