How Does the Organism Reproduce NCERT Solutions For Class 10th Science

CHAPTER -8

HOW DOES ORGANISMS REPRODUCE ?

 

IN TEXT QUESTIONS WITH ANSWERS

Page No. 128

Q1. What is the importance of DNA copying in reproduction?
Ans. Importance of DNA copying in reproduction are as follows –
(i) DNA copying is the basis of inheritance of traits from parents to offspring.
(ii) During copying of DNA, sometimes slight variations occur which form the basis for evolution.

Q2. Why is variation beneficial to the species but not necessarily for the individual ?
Ans. Variation is beneficial to the species but not necessarily for the individual because sometimes variation in an individual may results in death of that individual but for species variation results in the existence of that species. For example, if there is a population of certain bacteria living in normal climatic conditions and the temperature increases due to global warming, then most of these bacteria will not be able to tolerate excessive heat and hence die. But some bacteria which had variations to resist heat would survive and grow further. So, we can say, variation is beneficial to species but not necessarily for the individual.

Page No. 133

Q1. How does binary fission differ from multiple fission?
Ans.
Binary fission :
It is the process of asexual reproduction, in which parent organism divides to form two new organisms.
For eg. Amoeba-Amoeba reproduces by binary fission.

Multiple fission :
It is the process of asexual reproduction, in which parent organism divides to form many new organisms.
for eg. Plasmodium- Plasmodium reproduces by multiple fission.

Q2. How will an organism be benefited if it reproduces through spores?
Ans. The spores are covered by thick wall that protects them from unfavorable conditions like lack of food, water or high temperature. But as the conditions become favorable these spores can grow to produce new plant.
So, an organism will be benefited if it reproduces through spores.

Q3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Ans. Complex organisms have highly differentiated tissues and organs and not a single cell of a tissue is able to produce another type of tissue. For example, a dog is a complex multicellular organism and if we cut dog into two parts, then the cells of one part are not able to produce cells of other body part to produce a complete dog but in case of hydra (simple organism), regeneration takes place because cells in the cut body part are able to produce cells of other body parts.

Q4. Why is vegetative propagation practiced for growing some types of plants?
Ans. Vegetative propagation is practiced for growing some types of plants because of following advantages –
(i) It is used to grow a plant in which viable seeds are not formed or very few seeds are produced.
eg:- Orange, Banana, Pineapple.
(ii) It helps to introduce plants in new areas where the seed germination fails to produce mature plant
due to change in environmental factors and the soil.
(iii) It is more rapid, easier and cheaper method.
(iv) By this method a good quality of a race or variety can be preserved.

Q5. Why is DNA copying an essential part of the process of reproduction?
Ans. DNA contains the genetic information which transfers from parents to offspring and copying of DNA is the process in reproduction due to which genetic information transfers.

Page No. 140

Q1. How is the process of pollination different from fertilization?
Ans. Pollination – In this process pollen grains are transferred from anther to stigma of same flower or another flower.
(i) In this process no fusion of 2 cells take place.
Fertilization – It is defined as the fusion of male and female gametes to form zygote.
(ii) Fusion of 2 cells, male gamete and female gametes, take place.

Q2. How is the role of seminal vesicles and prostate gland?
Ans. Seminal vesicles and prostate gland are the part of male reproductive system and their functions are-
(i) Both add their secretions to vas deferens which carries sperms from the testes, thus makes the transport of sperms easier.
(ii) Provide nutrition to the sperms.

Q3. What are the changes seen in girls at the time of puberty?
Ans. Changes seen in girls at the time of puberty are:
(i) Mammary glands develop and increase in size.
(ii) Menstruation starts.
(iii) Hairs grow in armpits and pubic regions.
(iv) Extra fat deposited in thighs and hips and in other body parts.

Q4. How does the embryo get nourishment inside the mother’s body?
Ans. The embryo gets nourishment through placenta inside the mother’s body.
Placenta is disc-shaped tissue which connects the mother body and embryo.

Q5. If a woman is using a copper- T, will it help in protecting her from sexually transmitted disease?
Ans. No, using a copper-T will not help a woman in protecting her from sexually transmitted disease.

 

TEXTBOOK EXERCISE

Q1. Asexual reproduction takes place through budding in
(a) Amoeba
(b) Yeast
(c) Plasmodium
(d) Leishmania.
Ans. (b) Yeast

Q2. 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

Q3. The anther contains
(a) Sepals
(b) Ovules
(c) Carpel
(d) Pollen grains.
Ans. (d) Pollen grains.

Q4. What are the advantages of sexual reproduction over asexual reproduction?
Ans. Sexual reproduction leads to variation due to recombination of genetic material DNA. These variations are essential for the survival of species. On the contrary, asexual reproduction does not bring about variations.

Q5. What are the functions performed by the testis in human beings?
Ans. In human beings, testes perform a dual function:
(i) Production of sperms
(ii) Secretion of the male hormone testosterone.

Q6. Why does menstruation occur?
Ans. When in a human female if the egg is not fertilized, it lives for about one day. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilized egg. Thus, its lining becomes thick and spongy. This would be required for nourishing the embryo if had fertilized. However, this lining is not required any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucus. This cycle takes roughly every month and is known as menstruation.

Q7. Draw a labeled diagram of the longitudinal section of a flower.
Ans.

Q8. What are the different methods of contraception?
Ans. Various methods used for regulation of childbirth can broadly categories as:
(i) Barrier methods: In this method, physical devices such as a condom, diaphragm, cervical cap and Copper-T are used.
(ii) Chemical method: use of spermicidal jelly by a woman, oral pills, and vaginal pills.
(iii) Surgical method: In surgical method, a small portion of vasdeferens in male and the oviduct of female, is surgically removed or ligated. It is called vasectomy in male and tubectomy in females.

Q9. How are the modes of reproduction different in a unicellular and multicellular organism?
Ans. In unicellular organisms, cell division, or fusion leads to the creation of new individuals.
In multicellular organisms with simple body organization budding, fragmentation may work but in complex multicellular organisms, only sexual reproduction takes place.

Q10. How does reproduction help in providing stability to populations of species?
Ans. The consistency of DNA copying during reproduction is important for the maintenance of body design features that allow the organism to use the particular niche. Reproduction is, therefore, linked to the stability to populations of species.

Q11. What could be the reasons for adopting contraceptive methods?
Ans. The sexual act always has the potential to lead to pregnancy. Pregnancy will make major demands on the body and the mind of the woman and if she is not ready for it, her health will adversely affect. Therefore, adopting contraceptive methods are essential. Some contraceptive methods like condom also prevent spread of STDs and lethal diseases like HIV-AIDS.

 

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