NCERT Solutions How do Organisms Reproduce
1.What is the importance of DNA copying in reprod
uction? Ans.DNA contains information for the inheritance of features from parents to next generation. DNA presents in nucleus of cells are th e information source for making protein. If information is different, different pro tein will be made that lead to altered body design.
2.Why is variation beneficial to the species but not necessarily for the individual?
Ans.Variations are useful for the survival of speci es 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 b e wiped out. However, some variations are present some species will survive. T hus, variation is useful to species but not the individual.
page no.133
1. How does binary fission differ from multiple fis sions?
Ans.
2. How will an organism be benefited if it reproduc e through spores?
Ans.he spores are covered by thick walls that prot ect them until they come into contact with suitable moist surface and can begin to grow.
3. Can you think of reasons why more complex organi sm cannot give rise to new individuals through regeneration?
Ans.The reason is that complex organisms are not me rely random collection of cells. Specialized cells are organized in them as tissues are organized in organs. These organs have to be placed at definite positions in t he body. So, regeneration is not possible in multicellular organism.
4. Why is vegetative propagation practiced for grow ing some types of plants?
Ans.) Plants raised by vegetative propagation can bear flower and fruits earlier than those produced from seeds.
(ii) Such methods also make possible the propagati on of plants such as banana, orange, rose and jasmine that have lost the capacit y to produce seeds.
(iii) All plants produced by this method are genet ically similar enough to the parent plant to have its all characteristics.
5. Why is DNA coping essential part of the process of reproduction?
Ans.NA contains information for the inheritance of features from parents to next generation. DNA presents in nucleus of cells are th e information source for making protein. If information is different, different pro tein will be made that lead to altered body design.
Page no.140
1. How is process of pollination different from fe rtilization?
Ans.
2. What is the role of the seminal vesicles and th e prostate gland?
Ans.Secretions of seminal vesicles and prostate glan d 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?
Ans.During puberty breast size begins to increase wi th 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?
Ans.The embryo gets nutrition from the mother’s bloo d with the help of a special tissue called placenta. This is a disc which is embedded i n the wall of uterus. It contains finger-like projections villi on the embryo’s side of the tissue. On mother’s sides are blood spaces, which surround the villi. This provid es a large surface area for glucose and oxygen to pass the mother to the embryo and was te products from embryo to mother.
5. If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?
Ans. Copper-T cannot protect the woman from acquiring sexually transmitted disease. It will protect her from only unwanted pregnancy.
TExt book exercise question and answers
4. What are the advantages of sexual reproduction o ver asexual reproduction?
Ans.exual reproduction leads to variation due to r ecombination of genetic material DNA. These variations are essential for survival of species. On the contrary, asexual reproduction does not bring about variations.
5. What are the functions performed by the testis i n human beings?
Ans. In human beings, testes performs dual function: (i) Production of sperms (ii) Secretion of male hormone testosterone.
6. Why does menstruation occurs.
Ans.When in human female if the egg is not fertiliz ed, 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 fertilize d. However, this lining is not required any longer. So, the lining slowly breaks a nd comes out through the vagina as blood and mucous. This cycle takes roughly every month and is known as menstruation.
7. Draw a labeled diagram of the longitudinal secti on of a flower.
Ans.
8. What are the different methods of contraception?
Ans.Various methods used for regulation of child bir th can broadly categories as:
(i) Barrier methods: In this method, physical devic es such as condom, diaphragm, cervical cap and copper-T are used.
(ii) Chemical method: use of spermicidal jelly by w oman, oral pills and vaginal pills.
(iii) Surgical method: In surgical method, a small portion of vas deferens in male and the oviduct of female, is surgically removed or lig ated. It is called vasectomy in male and Tubectomy in females.
9. How are the modes of reproduction different in u nicellular and multicellular organism?
Ans.n unicellular organisms, cell division, or fusi on leads to the creation of new individuals. In multicellular organisms with simple body organiz ation budding, fragmentation may work but in complex multicellular organisms onl y sexual reproduction takes place.
10. How does reproduction help in providing stabili ty to populations of species?
Ans.The consistency of DNA copying during reproduct ion is important for the maintenance of body design features that allow the organism to use the particular niche. Reproduction is, therefore, linked to the st ability to populations of species.
11. What could be the reasons for adopting contrace ptive metho
Ans.he 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 affected. Therefore, adop ting contraceptive methods are essential. Some contraceptive methods like condom a lso prevent spread of STDs and lethal diseases like HIV-AIDS.
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