Tuesday, January 10, 2012

Solved CBSE Board Questions 10th Biology- Ch How Do Organisms Reproduce?

Q1)What is the importance of DNA copying in reproduction?
Ans-DNA is the genetic material present in the cells of all organisms. The genetic information from,generation to generation is carried by DNA .It is therefore possible for the organism to produce organism of its own type due to DNA copying only. For the inheritance of traits of the parent,DNA copying is a must.DNA copying also brings about variation ,which forms the basis for the origin of new species.

Q2)What are the changes seen in girls at the time of puberty?
Ans-i) Enlargement of breasts with the darkening of skin of the nipples .
ii) growth of hair in the genital region and in armpits occurs.
iii) onset of menstruation .

Q3)If a woman is using a copper-Twill it help in protecting her from sexually transmitted
diseases(STD’s)?
Ans-No,using copper-T will not protect a woman against catching STD.Copper-T is a device which will only guard her against pregnancy .

Q4)Sexual reproduction is considered advantageous over asexual reproduction? Explain
Ans-Sexual reproduction ensures that large number of variations appear in the daughter organism constituting a population. This is made possible by the appearance of many new gene combinations which are contributed by the two parents. Sexual reproduction also ensures that the rate of appearance of new variations is speed up which is not achieved due to asexual reproduction.

Q5) Mention the changes observed in flower after fertilization.
Ans-a) ovary ripens and developed into fruit.
b) ovules develop into seed.
c) petals and sepals wither and drop.
d)stigma, style and stamens dry up and fall off.

Q6)Give the advantages of vegetative propagation.
Ans-1) it is much easier,lowcost,quicker method compared to sexual reproduction.
2) plants which produce non viable seeds or too few seeds or have lost the ability to produce seeds can be made to reproduce vegetatively to produce daughter organisms.
3) plants produced by vegetatively reproduction are genetically similar to the parent plant and show all the characteristics of the parent.

Q7) What is placenta? Give the significance of placenta
Ans-placenta is a disc like mass of nutritive tissue which develops on the inner wall of uterus where the fertilized egg is implanted. Placenta performs the following functions:
1)it provides all the nutrients such as glucose,proteins,minerals and vitamins to the foetus.
2)ti provides antibodies through the mother’s blood to the foetus.these antibodies provide immunity to the child after its birth against a number of diseases.
3)it also meets the oxygen requirement of the foetus and removes carbondioxide and other metabolic waste generated in the body of the foetus. These metabolic wastes are ultimately removed and excreted by mother’s excretory system.

Q8)Why is reproduction essential for a species?
Ans-reproduction is necessary for species in order to increase their numbers otherwise it will become extinct.

Q9)Name an organism which shows binary fission and another that shows multiple fission.
Ans-binary fission-Amoeba, multiple fission-material parasite.e.,plasmodium

Q10)Name a unicellular organism and also a multi-cellular organism that show budding process.
Ans-Unicellular-yeast, multicellular-hydra.

Q11)How do oral contraceptive pills prevent pregnancy?
Ans-oral pills do not allow release of ovum from the follicle to occur, so fertilization does not take place.

Q12)Which is the most effective contraceptive method which will not allow sexually transmitted diseases(STD’s) to spread?
Ans-mechanical barrier by condoms, cervical caps, etc.

Q13)Give one difference between zygote and embryo.
Ans-Zygote is single celled fusion product of sperm and ovum. Embryo is a multicellular product produced by mitotic divisions from zygote.

14)How does the embryo derive nutrition after getting implanted in the walls of uterus?
ans-the embryo derives nutrition after getting implanted in the walls of uterus through a disc like tissues called placenta which has villi like projections on embryo side and blood spaces on mother’s side. This enables transport of materials like amino acids,glucose and oxygen from mother to child.

Q15)What happens if the ovum does not fertilized in female body?
Ans-when the ovum does not get fertilized it lives for one day.As the preparations of the uterine lining are not needed any more, the lining breaks and comes out along with the unfertilized ovum through the vaginal path in form of blood discharge. This is known as menstruation as it happens once in a month and it lasts for 2-8 days.

Q16)What is the function of seminal vesicles and prostate gland in the male body?
Ans-they add their secretions to sperms in order to make the sperms lie in a fluid which makes their flow and transport easier and also provides nutrition to sperms.

Q17)Why are pair of testes located outside the male body?
Ans-the pairs of testes are located outside the body of the males because a temperature of 2-3 degrees C,less than the body temperature is required for production of sperms.

Q18)Give example of two bacterial and two viral diseases which are transmitted through sexual contact?
Ans-bacterial diseases-gonorrhoea and syphilis, viral diseases-AIDS and genital warts.

Q19)What factors have lead to adoption of contraceptive methods? give at least four factors.
Ans-factors are:
1)growing human population.
2)spread of sexually transmitted diseases like AIDS.
3)gap between children in a family so that both mother and child get proper nutrition.
4)maintenance of sexual health.

Q20)How do sperms reach the female genital tract? where does fertilization and implantation of the embryo takes place. For how long does the embryo remain attached to uterine walls.
Ans-sperms travel upwards through uterus to oviduct where they may meet an ovum and hence fertilize it. Fertilization takes place in oviduct to give rise to single celled zygote. The zygote divides to become multicellular embryo which gets fixed in uterus. The embryo remains attached in uterine walls throughout gestation period which is 40 weeks in humans.

Q21)How do variations help a genera to evolve?
Ans-variations are better for a species rather than an individual because the variations enable the organism to survive competently in changing environment. When these variations are passed to many organisms of same species it helps the new species to originate, as variations occur in their DNA which is the genetic material and controls entire metabolism.

Q22)What is the need for DNA to replicate during the process of reproduction?
Ans-the need for DNA to replicate is due to the DNA being an important molecule which controls all metabolism of the body by producing proteins. No parent can give its own genetic material, needs to replicate and get transferred to the germ cell which will carry the information. When germ cells of two parents fuse to give rise to zygote.

Q23)What are the basic principles for contraception? Explain at least 3 principles with example of the device used?
Ans-the basic principles are;
i)not allowing the sperm to unite with ovum-MECHANICAL barrier,e.g.condoms,cervical caps.
Ii)not allowing the ovum to be released-CHEMICAL barriers,e.g. oral pills.
iii)creating a block in a path of ovum or sperm-SURGICAL barriers,e.g.vasectomy on males and tubectomy in females.
iv)preventing pregnancy by not allowing implantation to take place by copper-T and loops.

Q24)Why must pollination occur before fertilization? How is pollination different from fertilization? What does a pollen contain inside?
Ans-pollination must occur before fertilization as it has to reach the male gametes present in pollen grain which will germinate to form a pollen tube and carry the male gametes to the ovum. Pollination is different from fertilization Because here the pollen grain with its male gametes just reaches the stigma, whereas fertilization of male gamete to ovum results in formation of diploid zygote which is the foundation of new generation.

Q25)Give differences between asexual and sexual modes of reproduction.
Ans-asexual reproduction
1.only one parent is involved to form an offspring.
2.it does not lead to variations.
3.generally occurs in unicellular organisms ,plants and sponges, like hydra
4.exact replicas of parents produced –can be called clones.
Sexual reproduction
1.two parent male and female are involved to give rise to an offspring.
2.it gives rise to variations.
3.occurs in higher animals which are multicellular and well developed.
4.theoffsprings are not exact replicas,they differ from their parents.

Q26)What is vegetative propagation? Give examples of plants which can be propagated by their: a)stems b)roots c)leaves
Ans-vegetative propagation is a method of reproduction in higher plants in which their vegetative parts are capable of giving rise to new plants .vegetative propagation can be natural or artificial.
1.Stems-potato,onion,ginger
2.roots- banana, asparagus
3.leaves- Bryophyllum

Q27)Give the functions of the following A)ovaries b)testes c)uterus d)vas deferens e)fallopian tube
Ans: a)ovaries produce ovum; once every month alternatively. they produce estrogen and progesterone hormone.
b) testes produce sperms and testosterone hormone.
c) uterus walls become thick to help in attachment of embryo,i.e.,implantation to occurs.
d)vas deferens- help to carry sperms from testes to seminal vesicles.
e) fallopian tube-fertilization tube- fertilization occurs here as sperms travel to reach vum.

Q28)what is binary fission?
Ans)Many bacteria and protozoa simply split into two equal halves during cell division. This process is called binary fission. In organisms such as Amoeba, the splitting of the two cells during division can take place in any plane.

Q29) what is multiple fission? Name the organism that shows this mode of reproduction.
Ans)Some single-celled organisms, such as the malarial parasite, Plasmodium, divide into many daughter cells simultaneously.This process is called multiple fission.

Q30) Define fragmentation?
Ans)In multi-cellular organisms with relatively simple body organisation,simple reproductive methods can still work. Spirogyra, for example,simply breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals.

Q31) Define regeneration?
Ans)Many fully differentiated organisms have the ability to give rise to new individual organisms from their body parts. That is, if the individual is somehow cut or broken up into many pieces, many of these pieces grow into separate individuals. For example, simple animals like Hydra and Planaria can be cut into any number of pieces and each piece grows into a complete organism. This is known as regeneration

Q32)Explain budding in Hydra.
Ans) Organisms such as Hydra use regenerative cells for reproduction in the process of budding. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals.

Q33) How does bryophyllum multiply asexually?
Ans)Buds produced in the notches along the leaf margin of Bryophyllum fall on the soil and develop into new plants.

Q34)Explain the reproduction in Rhizopus.
Ans) In Rhizopus,the tiny blob-on-a-stick structures are involved in reproduction. The blobs are sporangia, which contain cells, or spores, that can eventually develop into new Rhizopus individuals.The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.

Related study material:

10th Science SA-2 Chapter wise Test Papers Links
1. Carbon and Its Compounds                    
7. Our Environment                                   
3. How Do Organisms Reproduce?            
9. Science  Sample papers                            

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