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How do Organism Reproduce : NCERT Intext Questions


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Page 128, Page 133, Page 140
Page 128

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

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.

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

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 133

Q.1      How does binary fission differ from multiple fission?

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 :

(ii)   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.


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

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.

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

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.

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

Vegetative propagation is practiced for growing some types of plants because of following advantages -
It is used to grow a plant in which viable seeds are not formed or very few seeds are produced.
      eg:- Orange, Banana, Pineapple.
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.
It is more rapid, easier and cheaper method.
By this method a good quality of a race or variety can be preserved.

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

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 140

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

Pollination - In this process pollen grains are transferred from anther to stigma of same flower or another flower.
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.
Fusion of 2 cells, male gamete and female gametes, take place.

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

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.

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

Changes seen in girls at the time of puberty are:
Mammary glands develop and increase in size.
Menstruation starts.
Hairs grow in armpits and pubic regions.
Extra fat deposited in thighs and hips and in other body parts.

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

The embryo gets nourishment through placenta inside the mother's body.
Placenta is disc-shaped tissue which connects the mother body and embryo.

Q.5      If a woman is using a copper- T, will it help in protecting her from sexually transmitted disease?
Sol.        No, using a copper-T will not help a woman in protecting her from sexually transmitted disease.


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