NCERT Exemplar Class 10 Science Solutions for Chapter 8 How Do Organisms Reproduce

NCERT Exemplar Class 10 Science Solutions for Chapter 8 How Do Organisms Reproduce

NCERT Exemplar Class 10 Science Solutions for Chapter 8 How Do Organisms Reproduce

 
There are NCERT Exemplar Class 10 Science Chapter 8 How Do Organisms Reproduce? It is a important study material for class 10.
These Exemplar solutions are prepared according to the CBSE syllabus. I has 27 MCQs, 21 short question answers and 11 long question answers.
 

NCERT Exemplar Problems-

  • Multiple Choice Questions (MCQs)
1. In the list of organisms given below, those that reproduce by the sexual by the asexual method are :
(i) Banana
(ii) Dog
(iii) Yeast
(iv) Amoeba
(a) (ii) and (iv)         
(b) (i), (iii) and (iv)
(c) (i) and (iv) 
(d) (ii), (iii) and (iv) 
Solution : 
(b) (i), (iii) and (iv)
2. In a flower, the parts that produce male and female gametes (germ cells) are :
(i) Stamen and anther
(b) Filament and stigma
(c) Anther and ovary 
(d) Stamen and style
 
Solution :
(c) Anther and ovary
3. Which of the following is the correct sequence of events of sexual reproduction in a flower?
(a) Pollination, fertilization, seedling, embryo
(b) Seedling, embryo, fertilization, pollination 
(c) Pollination, fertilization, embryo, seedling
(d) Embryo, seedling, pollination, fertilisation
 
Solution :
(c) Pollination, fertilization, embryo, seedling
4. Offsprings formed by asexual method of reproduction have greater similarity among themselves because :
(i) Asexual reproduction involves only one parent.
(ii) Asexual reproduction does not involves gametes.
(iii) Asexual reproduction occurs before sexual reproduction.
(iv) Asexual reproduction occurs after sexual reproduction.
(a) (i) and (ii) 
(b) (i) and (iii) 
(c) (ii) and (iv) 
(d) (iii) and (iv)

Solution :
(a) (i) and (ii)
Explanation :
In asexual reproduction, only mitotic divisions occur so the individuals produced are genetically similar to the parental organism and also among themselves.

5. Characters transmitted from parents to offspring are present in :
(a) Cytoplasm
(b) Ribosome
(c) Golgi bodies
(d) Genes

Solution :
(d) Genes

6. Characters that are transmitted from parents to offspring during reproduction show :
(a) Only similarities with parents
(b) Only variations with parents
(c) Both similarities and variations with parents
(d) Neither similarities nor variations

Solution :
(c) Booth similarities and variations with parents.

7. A feature of reproduction that is common to Amoeba, Spirogyra and Yeast is that :
(a) They reproduce asexually.
(b) They are all unicellular.
(c) They reproduce only sexually.
(d) They are all multicellular.

Solution :
(a) They reproduce asexually

8. In spirogyra, asexual reproduction takes place by :
(a) Breaking up of filaments into smaller bits
(b) Division of a cell into two cells
(c) Division of a cell into many cells
(d) Formation of young cells from older cells. 

Solution :
(a) Breaking up of filaments into smaller bits

9. The ability of a cell to divide into several cells during reproduction in Plasmodium is called :
(a) Budding
(b) Reduction division
(c) Binary fission
(d) Multiple fission

Solution :
(d) Multiple fission

10. The correct sequence of reproductive stages seen in flowering plants is :
(a) Gametes, zygote, embryo, seedling

(b) Zygote, gametes, embryo, seedling
(c) Seedling, embryo, zygote, gametes
(d) Gametes, embryo, zygote, seedling

Solution :
(a) Gametes, zygote, embryo, seedling

11. The number of chromosomes in parents and offsprings of a particular species remains constant due to :
(a) Doubling of chromosomes after zygote formation
(b) Halving of chromosomes during gamete formation
(c) Doubling of chromosomes after gamete formation
(d) Halving of chromosomes after gamete formation

Solution :
(b): Sexual reproduction involves gametogenesis followed by fertilization

12. In Rhizopus, tubular thread like- structures bearing sporangia at their tips are called :
(a) Filaments
(b) Hyphae
(c) Rhizoids
(d) Roots

Solution :
(b) Hyphae

13. Vegetative propagation refers to formation of new plants from :
(a) Stem, roots and flowers
(b) Stem, roots and leaves
(c) Stem, flowers and fruits
(d) Stem, leaves and flowers

Solution :
(a) Stem, roots and flowers

14. Factors responsible for the rapid spread mould on slices of bread are :
(i) Large number of spores
(ii) Availability of moisture  and nutrients in bread
(iii) Presence of tubular branched hyphae
(iv) Formation of round shaped sporangia
(a) (i) and (iii)
(b) (ii) and (iv) 
(c) (i) and (ii) 
(d) (iii) and (iv)

Solution :
(c) (i) and (ii)

15. Length of pollen tube depends on the distance between :
(a) Pollen grain and upper surface of stigma. 
(b) Pollen grain on upper surface of stigma and ovule.
(c) Pollen grain in anther and upper surface of stigma.
(d) Upper surface of stigma and lower part of style.

Solution :
(b) Pollen grain on upper surface of stigma and ovule,

16. Which of the following statements are true for flowers?
(i) Flowers are always bisexual.
(ii) They are the sexual reproductive organs
(iii) They are produces in all groups in plants.
(iv) After fertilisation they give rise to fruits
(a) (i) and (iv)
(b) (ii) and (iii) 
(c) (i) and (iii)
(d) (ii) and (iv)

Solution :
(d) (ii) and (iv)

17. Which among the following statements are true for unisexual flowers?
(i) They possess both stamen and pistil.
(ii) They possess either stamen or pistil.
(iii) They exhibit cross pollination
(iv) Unisexual flowers possessing only stamens cannot produce fruits.
(a) (i) and (iv) 
(b) (ii), (iii) and (iv)
(c) (iii) and (iv) 
(d) (i), (iii) and (iv) 

Solution :
(b) (ii), (iii) and (iv)

18. Which among the following statements are true for sexual reproduction in flowering plants?
(i) It requires two types of gametes.
(ii) Fertilization is a compulsory event
(iii) It always result in formation of zygote.
(iv) Offspring formed are clones.
(a) (i) and (iv)
(b) (i), (ii) and (iv)
(c) (i), (ii) and (iii)
(iv) (i), (ii) and (iv)

Solution :
(c) (i), (ii) and (iii)

19. In figure, the parts A, B and C are sequentially :

(a) Cotyledon, plumule and radicle
(b) Plumule, radicle and cotyledon
(c) Plumule, cotyledon and radicle
(d) Radicle, cotyledon and plumule

Solution :
(c) Plumule, cotyledon and radicle

20. Offsprings formed as a result of sexual reproduction exibhit more variations because :
(a) Sexual reproduction is a lengthy process.
(b) Genetic material comes from two parents of the same species.
(c) Genetic material comes from two parents of different species.
(d) Genetic material comes from many parents.

Solution :
(b) : In sexual reproduction, variations appear at the time of crossing over during prophase-I of meiosis and the chance fusion of gametes of two different parents.

21, Reproduction is essential for living organisms in order to :
(a) Keep the individual organism alive.
(b) Fulfill their energy requirement.
(c) Maintain growth.
(d) Continue the species generation after generation.

Solution :
(d) Continue the species generation after generation.

22. During, adolescence, several changes occur in the human body. Mark ine change associateed with sexual maturation in boys :
(a) Loss of milk teeth
(b) Increase in height
(c) Cracking of voice
(d) Weight gain

Solution :
(c) Cracking of voice

23. In human females, an event that reflects on set of reproductive phase of :
(a) Growth of body.
(b) Changes in hair pattern.
(c) Change in voice.
(d) Menstruation.
Solution :
(d) : Puberty if human female is characterized by beginning of ovulation and mensturation as the primary follicles remain immature upto puberty.

24. In human males, the testes lie in the scrotum, because it helps in the :
(a) Process of mating.
(b) Formation of sperm.
(c) Easy transfer of gametes.
(d) All of the above.

Solution :
(b) Formation of sperm.

25. Which among the following is not the function of testes at puberty?
(i) Formation of germ cells.
(ii) Secretion of testosterone.
(iii) Development of placenta.
(iv) Secretion of estrogen.
(a) (i) and (ii) 
(b) (ii) and (iii)
(c) (iii) and (iv) 
(d) (i) and (iv)

Solution :
(c) (iii) and (iv)

26. The correct sequence of organs in the male reproductive system for transport of sperm is :
(a) Testis, vas deferens, urethra
(b) Testis, ureter, urethra
(c) Testis, urethra, ureter
(d) Testis, vas deferens, ureter

Solution :
(a) Testis, vas deferens, urethra

27. Which among the following diseases is not sexually transmitted?
(a) Syphilis
(b) Hepatitis
(c) HIV- AIDS
(d) Gronorrhoea

Solution :
(b) Hepatitis

  • Short Answer Questions

1. In a bisexual flower inspite of the young stamens being removed artificially, the flower produces fruit. Provide a suitable explanation for the above situation.

Solution :
Because as the carpels are intact so fertilization may occur by cress-pollination. This leads to fertilization and formation fruit.
 
2. Can you consider cell division as a type of reproduction in unicellular organism? Give one reason.
Solution :
In Amoeba, Paramecium and Euglena, new individuals are formed by binary fission which involves karyokinesis and cytokinesis, the processes involved in cell division.
 
3. What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?
Solution :
A clone is the group of genetically similar individuals. Since the members of a clone are formed by mitotic division during asexual reproduction se are genetically similar ans exhibit remarkable similarity.
 
4. Explain hoe, offspring and parents of organisms reproducing sexually have the same number of chromosomes?
Solution :
Reduction division (meiosis) during gamete formation halves the chromosomes number in both male and female gametes. Since these two gametes fuse during fertilisation, the original number of chromosomes (as in the parent) is restored in the offspring. 
 
5. Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this.
Solution :
Sugar provides energy for sustaining all life activities in yeasts. In water, it fails to reproduce because of inadequate energy in its cells.
 
6. Why does bread mould grow profusely in a moist slice of bread rather than on a dry slice of bread?
Solution :
Moisture is an important factor for the growth of hyphae. Moistened bread slice offers both moisture and nutrients to the bread mould, hence it grows profusely, Dry slice of bread offers nutrients but not moisture hence hyphae fail to grow.
 
7. Give two reasons for the appearance of variations among the progeny formed by sexual reproduction. 
Solution :
(a) Different combination of genes are formed during crossing over of meiosis which occurs during formation of gametes.
(b) Fertilization is chance fusion of gametes so combines the genetic material of two different parents so producing new gene combinations.
 
8. Would a planaria cut vertically into two halves regenerate into two individuals? Complete figure D and E by indicating the regenerated regions. 
Solution :


Yes. Each half of Planaria will develop the missing half as shown in the figure.


9. From the internet, gather information about the chromosomes numbers of five animals and five plants. Correlate the number with the size of organism and answer the following questions:
(a) Do larger organisms have more number of chromosomes/ cells?
(b) Can organism with fewer chromosomes reproduce more easily than organisms with more number of chromosomes ? 
(c) More the number of chromosomes/ cells greater is the DNA content. justify.
Solution :
(a) No, there is no relationship between size of organism and its chromosomes number.
(b) No, process of reproduction follows a common pattern and is not dependent on the number of chromosomes.
(c) Yes, since the major component of chromosome is DNA, if there are more chromosomes in a cell the quantity of DNA will also be more.

10. In tobacco plant, the male gametes have twenty four chromosomes. What is the number of chromosomes in the female gamete?
What is the number of chromosomes in the zygote?  

Solution :
(a) Number of chromosomes in the female gamete = 24.
(b) Number of chromosomes in the zygote = 48.

11. Why cannot fertilisation take place in flowers if pollination does not occur ?
Solution :
If pollination does not occur then fertilisation cannot take place because male gamete will not be available. For fertilisation, both male and female gametes must be present.

12. Is the chromosome number of zygote, embryonal cells and adult of a particular organism always constant? How is the constancy maintained in these three stages?
Solution :
Chromosomes number in zygote, embryonal cells and adult of a particular organism is always same because embryonal cells and adult are formed by mitotic divisions of zygote.

13. Where the zygote located in the flower after fertilization?
Solution :
Zygote is located inside the ovule present inside the ovary of carpel.

14. Reproduction is linked ti stability of population of a species. justify the statement.
Solution :
In reproduction, DNA passes from one generation to the next. Copying of a DNA takes place with consistency but with minor variations. This consistency leads to stability of species. 

15. How are general growth and sexual maturation different from each other ? (CBSE Sample Paper-II : 02 Marks)
Solution :
General growth refers to different types of developmental processes in the body like increase in height, weight gain, changes in shape and size of the body but sexual maturation is specific to changes reflected at puberty like cracking of voice, new hair patterns, development of breast in female etc.

16. Trace the path of sperm during ejaculation and mention the glands and their functions associated with the male reproductive system.
Solution :
(a) Path of sperm : Testis, Epididymis, Vas deferens, Urethra, Ejaculated.
(b) Male reproductive glands : (i) Prostate gland; (ii) Seminal vesicles and Cowper’s glands. Secretion of these glands provides nutrition to sperms and helps in transfer to sperms into vagina.

17. What changes are observed in the uterus if fertilisation does not occur ?
Solution :
The thick and spongy lining of the uterus slowly breaks and comes out through the vagina with blood and mucus.

18. What changes are observed in the uterus subsequent to implantation of young embryo?
Solution :
The uterine wall thickens that is richly supplied with blood. A special tissue and called placenta develops which connects embryo to the uterine wall that provides nutrients and oxygen to it.

19. What are the benefits of using mechanical barriers during sexual act?
Solution :
Mechanical barriers like condoms have following benefits :
(a) Prevent the deposition of sperms in vagina so avoid pregnancy.
(b) Prevent the transmission of STDs like syphilis, AIDS, etc.

20. In the given Figure, label the parts that mention their functions :
(a) Production of egg
(b) Site of fertilisation
(c) Site of implantation
(d) Entry of the sperms

Solution :
(a) Ovary
(b) Fallopian tube
(c) Uterine endometrium
(d) Vagina

21. What would be the ratio of chromosomes number between an egg and its zygote? How is sperm genetically different from the egg ?
Solution :
(a) Ratio of chromosomes : 
Egg : Zygote
1 : 2
(b) Sperm has either X and Y sex chromosome while female egg always has an X-chromosome.

  • Long Answer Questions

1. Why are budding, fragmentation and regeneration all considered as asexual types of reproduction? With neat diagrams explain the process of regeneration in planaria.
Solution :
(i) Budding, fragmentation and regeneration all are considered as asexual modes of reproduction as :
(a) All are uniparental.
(b) There is no formation and fusion of gametes.
(ii) Regeneration in Planaria

2. Write two points of difference between asexual and sexual types of reproduction. Describe why variations are observed in the offspring formed by sexual reproduction.
Solution :
(i) Differences :
(a) Asexual reproduction is always uniparental while sexual reproduction is generally biparental.
(b) sexual reproduction involves formation of gametes by meiosis followed by fusion of gametes called fertilization. But in asexual reproduction there is no formation and fusion of gametes and only mitotic divisions occur.
(ii) In sexual reproduction, variations appear due to formation of new combinations of genes during :
(a) Crossing over in meiosis during gameto-genesis.
(b) Fertilization involves chance fusion of gametes.

3. Distinguish between pollination and fertilization. Mention the site and product of fertilization in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule. (CBSE Sample Paper-I : 05 Marks)
Solution :
(a) Pollination involves transfer of pollens from anther to stigma of same or different flower, while fertilisation involves fusion of male and female gametes to form diploid zygote.
(b) Site of fertilisation is ovule inside the ovary and the fusion product is called zygote.
(c) See Fig. in of the chapters

4. Distinguish between a gamete and zygote. Explain their role in sexual reproduction.
Solution :
(a) Gamete is the sex cell of an individual and is sperm in male and ovum in female.
(b) Gametes are haploids as are formed the genes and character of two different parents to form a diploid zygote, while zygote is first cell of next generation and grows by mitosis to develop into new individual.

5. Draw the diagram of a flower and label the four whorls. Write the names of gamete-producing organs in the flower.
Solution :
(a) Diagram of the flower.
(b) Male gamete-producing organ is stamen/ Anther.
(c) Female gamete producing organ is pistil/ovary/ovule.

6. What is placenta? Mention its role during pregnancy?
Solution :
(a) Placenta in an intimate mechanical and physiological connection between the foetal and maternal tissue.
(b) Role during pregnancy :
(i) Embryo produces finger-like processes, called villi, in the endometrial tissue.Villi increase surface area of exchange of materials.
(ii) It helps in nutrition, respiration, excretion, etc. of the foetus.
(iii) It secretes human chorionice gonadotropin, (HCG) which maintains pregnancy.

7. What are various ways to avoid pregnancy? Elaborate any one method.
Solution :
Pregnancy can be avoided by following methods :
(a) Mechanical barriers like condoms, cervical caps and Intra-uterine devices (IUDs).
(b) Chemical methods like Mala-D, Saheli and i-pill.
(c) Surgical methods like vasectomy in male, tubectomy in female, castration in male, ovariectomy in female, etc.
(d) Natural methods e.g. intercourse during one week after and one week before the menstrual phase.
Chemical methods of birth Control :
(a) Spermicidal tablets, creams or pastes to be introduced in vagina before intercourse to kill the sperms.
(b) Combined birth control pills like Mala-D, Saheli, etc. are taken orally and inhibit ovulation from the ovary.


8. How does fertilisation take place? Fertilisation occurs once in month. Comment.
Solution :
(i) Mechanism of fertilization : (a) Semen is deposited in vagina during intercourse.
(b) Sperms swim upward and reach Fallopian tube through uterus.
(c) Ovulation occurs and ovum is trapped by Fallopian funnel.
(d) Ovum reaches fallopian tube by peristalsis.
(e) Sperm enters ovum with the help of enzyme hyaluronidase.
(ii) Because only one ovum us released by human ovary in a month.

9. Reproduction is essentially a phenomenon that is not for survival of an individual but for the stability of a species. justify.(CBSE Sample Paper-I : 05 Marks)
Solution :
(a) Organisms need energy for survival which they obtain from life processes such as nutrition and respiration.
(b) Reproduction needs a lot of energy.
(c) Genetic material is transferred from one generation to the next as a result of reproduction through DNA copying.
(d) DNA copying tales place with high constancy and considerable variations, that is, advantages to the species for stability in the changing environment.

10. Describe sexually transmitted diseases and mention the ways to prevent them.
Solution :
(a) Sexually-transmitted diseases (STDs) are infectious and communicable diseases which are transmitted during unsafe sexual act.
(b) Bacterial STDs are : Syphilis, Gonorrhoea, Chlamydiosis, etc.
(c) Viral STDs are : Hepatitis-B, AIDS, Genitalherpes, Genital warts, etc.
(d) STDs can be prevented by using condoms and avoiding prositution.

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