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NCERT Exemplar Class 10 Science Chapter 8 How do Organisms Reproduce? Solutions

NCERT Exemplar Solutions for Class 10 Science Chapter 8 How do Organisms Reproduce covers all the important questions and answers as well as advanced level questions. It helps in learning about the sexual and asexual reproduction, pollination, reproduction in flowers, fertilization, genetics and human reproductive system.

The NCERT Exemplar solutions for class 10 science is very important for board exams. NCERT Exemplar Solutions for Class 10 Science Chapter 8 How do Organisms Reproduce is provided by our experts. They prepared the best solutions which help the students in understanding the solutions in an easy way. This chapters also covers the other topics like chromosomes, physical barriers, sexually transmitted diseases.


Chapter Name

Chapter 8 How do Organisms Reproduce

Book Title

NCERT Exemplar for Class 10 Science

Related Study

  • NCERT Solutions for Class 10 Science Chapter 8 How do Organisms Reproduce
  • Revision Notes for Class 10 Science Chapter 8 How do Organisms Reproduce
  • MCQ for Class 10 Science Chapter 8 How do Organisms Reproduce
  • Important Questions for Class 10 Science Chapter 8 How do Organisms Reproduce

Topics Covered

  • MCQ
  • Short Answers Questions
  • Long Answers Questions

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

Multiple Choice Questions

1. In the list of organisms given below, those that reproduce 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) 

Dog reproduce sexually, yeast reproduce by budding, Amoeba reproduce sexually and cultivated banana also reproduce asexually.


2. In a flower, the parts that produce male and female gametes (germ cells) are
(a) 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, fertilisation, seedling, embryo
(b) seedling, embryo, fertilisation, pollination
(c) pollination, fertilisation, embryo, seedling
(d) embryo, seedling, pollination, fertilization

Solution
(c) pollination, fertilisation, embryo, seedling

Pollination leads to fertilization. After this embryo is formed. Seedling comes out from the embryo.


4. Offspring formed by asexual method of reproduction have greater similarity among themselves because
(i) asexual reproduction involves only one parent
(ii) asexual reproduction does not involve 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)

Single parent is involved in asexual reproduction and thus there will be no exchange of gametes. This is the reason why offspring looks similar to their parent..


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) both 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 

Amoeba reproduces by binary fission, Spirogyra reproduces by fragmentation and yeast reproduces by budding.

 

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

Spirogyra reproduces by fragmentation. Upon maturation, the spirogyra simply breaks up into smaller pieces. These pieces or fragments grow into new individuals.


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

Plasmodium divides into many daughter cells by binary multiple fissions. In multiple fission nucleus of the cell divides multiple times by mitosis and then separates to create multiple daughter cells.


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

During fertilization, gametes fuse to form a zygote. Embryo will be formed after fertilization which leads to seedling in plants.


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) halving of chromosomes during gamete formation

The number of chromosome is halved during gamete formation. The number of chromosome remains the same as that in somatic cell of an organism.


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 

Tiny blob-on-a-stick like structures involved in reproduction are called hyphae. The blobs are called sporangia, which contain cells, or spores, that can eventually develop into new rhizopus individuals.


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
(b) stem, roots and leaves

Vegetative propagation is a type of asexual reproduction which occurs in plants. Anew plant is produced from the vegetative parts of the plants such as roots, stem, leaf and buds. The plants produced in vegetative reproduction are genetically similar enough to the parent plant.


14. Factors responsible for the rapid spread of bread 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) 

Large number of spores ensures that a few of them survive even in adverse conditions. Availability of moisture and nutrients in the bread provides necessary environment for spore to grow into mould.


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
(d) upper surface of stigma and lower part of style

The length of the pollen tube ensures that the pollens reach the stigma to conduct pollination.


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 produced in all groups of 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) 

Flowers are not always bisexual. Only angiosperms produce flowers.


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)

Unisexual flowers possess either stamen or pistil, hence cross pollination is necessary. Fruit is a mature ovary, hence the flowers possessing only stamens cannot produce fruits.


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

(a) (i) and (iv)
(b) (i), (ii) and (iv)
(c) (i), (ii) and (iii)
(d) (i), (ii) and (iv)

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

Off-springs produced by sexual reproduction cannot be clones.


19.In Figure 8.1, 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. Offspring formed as a result of sexual reproduction exhibit 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) genetic material comes from two parents of the same species 

Zygote is formed by gametes produced by a male and a female in sexual reproduction. Zygote on fertilization produces new offspring. Offsprings incur more variations as there is contribution from two 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

Reproduction is essential to the lineage of a species whereas other life processes are essential to keep the organism alive.


22. During adolescence, several changes occur in the human body. Mark one change associated 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

During adolescence the following changes occur in boys:

  • Growth of hairs in armpits, between thighs, near genital organ, thin hairs on face, legs and on arms.
  • Creaking of voice
  • Skin becomes oily and pimples start appearing.


23. In human females, an event that reflects onset of reproductive phase is
(a) growth of body
(b) changes in hair pattern
(c) change in voice
(d) menstruation
Solution
(d) menstruation

During adolescence following changes occur in boys:
  • Growth of hairs in armpits, between thighs, near genital organ, thin hairs on face, legs and on arms.
  • Creaking of voice
  • Skin gets oily and pimples appear.

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 the above
Solution
(b) formation of sperm 

Testes ensure that the temperature of the testes remains lower than the body temperature which helps in sperm production.

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)
Testis is the male reproductive organ but estrogen is produced in females. Placenta is formed in females during pregnancy.

26. The correct sequence of organs in the male reproductive system for transport of sperms is
(a) testis → vasdeferens → urethra
(b) testis → ureter → urethra
(c) testis → urethra → ureter
(d) testis → vasdeferens → ureter
Solution
(a) testis → vasdeferens → urethra
Sperm is produced in the testis and from there it is transferred into epididymis through the vasdeferns. Finally from vasdeferens the sperm is taken to urethra.

27. Which among the following diseases is not sexually transmitted?
(a) Syphillis
(b) Hepatitis
(c) HIV - AIDS
(d) Gonorrhoea
Solution
(b) Hepatitis
Hepatitis spreads through contaminated water and food. 

Short Answer Questions

28. 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
The pistil remains intact. Cross pollination might have occurred leading to fertilisation and formation of fruit.

29. Can you consider cell division as a type of reproduction in unicellular organism? Give one reason.
Solution
Cell division can be considered as a type of reproduction in unicellular organisms because it results in the formation of two daughter cells. That is it results in the production of more individuals of the organism.

30. What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?
Solution
The offspring of an organism formed by asexual method of reproduction is referred to as a clone. Clones exhibit remarkable similarity as they possess exact copies of the DNA of their parent.

31. Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes?
Solution
During gamete formation, deduction division (meiosis) halves the chromosome number in both male and female gametes. As these two gametes fuse during fertilisation, the original number of chromosomes (as in the parent)is restored in the offspring.

32. Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this.
Solution
In yeasts, sugar provides energy for sustaining all life activities. Yeast fails to reproduce in because of inadequate energy in its cells. 

33. Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?
Solution
For the growth of hyphae moisture is an important factor. Moistened bread slice offers both moisture and nutrients to the bread mould, hence it grows profusely. Hyphae fail to grow on dry slice of bread as it offers nutrients but not moisture. 

34. Give two reasons for the appearance of variations among the progeny formed by sexual reproduction. 
Solution
  • Two parents with different sets of characters are involved in sexual reproduction.
  • In gametes, the gene combinations are different.

35. Would a Planaria cut vertically into two halves regenerate into two individuals? Complete Figure 8.2 D and E by indicating the regenerated regions.
Solution
The shaded part in Figures D and E represent the regenerated halves.

36. From the internet, gather information about the chromosome 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

Animals

Chromosome numbers

Plants

Chromosome numbers

Man

46

Corn

20

Cat

38

Cotton

52

Horse

64

Garden pea

14

Rabbit

44

Mango

40

Elephant

56

Onion

16

(a) There is no relationship between size of organism and its chromosome number. 
(b) The process of reproduction follows a common pattern and is not dependent on the number of chromosomes.
(c) As the major component of chromosome is DNA, so if there are more chromosomes in a cell, the quantity of DNA will also be more.

37. 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
Number of chromosomes in female gamete is 24.
Number of chromosomes in zygote is 48.

38. Why cannot fertilisation take place in flowers if pollination does not occur?
Solution
Flower fertilisation requires both male and female gametes. Therefore, if pollination does not occur, male gamete won’t be available and hence fertilisation cannot take place.

39. 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
Yes, the constancy is maintained as the cells in all these three structures undergo only mitotic divisions.

40. Where is the zygote located in the flower after fertilization ? 
Solution
Zygote is located inside the ovule which is present in the ovary. 

41. Reproduction is linked to stability of population of a species. Justify the statement.
Solution
In the process of reproduction, DNA passes from one generation to the next. DNA copying takes place with consistency but with minor variations. This consistency leads to stability of species. 

42. How are general growth and sexual maturation different from each other ? 
Solution
Different types of developmental process in the body like increase in height, weight gain, changes in shape and size of the body are referred to as general growth but sexual maturation is specific to changes reflected at puberty like cracking of voice, new hair patterns, development of breast in female etc.

43. Trace the path of sperm during ejaculation and mention the gland and their functions associated with the male reproductive system.
Solution
From the testis the sperms come into the vas deferens and then pass through the urethra before ejaculation. The secretions from the seminal vesicle and prostrate glands provide nutrition to the sperms and facilitate their transport.

Gland associated with male reproductive system

Function

Testes

Secretion of testosterone

Prostate gland

Makes the medium of semen alkaline

Seminal vesicle

Addition of fluid content to semen

Cowper’s gland

Urethra lubrication and neutralizes acidic traces of urine.


44. What changes are observed in the uterus if fertilisation does not occur?
Solution
Following changes occur in the uterus if fertilization does not occur 
  • Slowly the thick and spongy lining of the uterus breaks and comes out through the vagina as blood and mucus.
  • Unfertilized egg gets discharged 
  • Menstruation takes place 

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

46. What are the benefits of using mechanical barriers during sexual act?
Solution
Mechanical barriers like condom prevent the sperms from reaching the egg. Thereby it is an effective method to avoid pregnancy. It also prevents transmission of infections during sexual act.

47. In the given Figure 8.3 label the parts and mention their functions 
(a) Production of egg 
(b) Site of fertilisation 
(c) Site of implantation 
(d) Entry of the sperms
Solution
(a) Ovary 
(b) Oviduct 
(c) Uterus 
(d) Vaginal passage

48. What would be the ratio of chromosome number between an egg and its zygote? How is the sperm genetically different from the egg?
Solution
The ratio of chromosome number between an egg and its zygote is 1 : 2. Sperms contain either X or Y chromosome whereas an egg will always have an X chromosome

Long Answer Questions

49. Why are budding, fragmentation and regeneration all considered as asexual types of reproduction? With neat diagrams explain the process of regeneration in Planaria.
Solution
Budding, fragmentation and regeneration involve only one parent and gametes are not involved in reproduction. Hence they are considered as asexual type of reproduction.
Regeneration of Planaria
Here the body of planaria cut into pieces and each piece has the ability to grow into new organism. In the figure above planaria body is cut into 3 pieces which regenerates into 3 individual cells.

50. 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 

Sexual reproduction

Asexual reproduction

Two parents are involved

Single parent is involved

Gametes are formed

Gametes are not formed

Sexual reproduction produces offsprings with more variations as compared to asexual mode of reproduction. The reasons for the same are as follows:
  • Both the parents contribute to the gene pool.
  • Crossing over during meiosis results in more variation.
  • DNA replication also contributes for the variation.

51. Distinguish between pollination and fertilisation. Mention the site and product of fertilisation in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule. 
Solution

Pollination

Fertilization

It is the transfer of pollen grains from the anther to the stigma of a flower.

It is the fusion of male gamete with female gamete.

Achieved by agents like a wind, water or animals.

Achieved by the growth of pollen tube so that the mail gamete reaches the female germ cells.

Leads to fertilization

Lead to formation of seeds

Pollination is an external process

Occurs in the ovary of female.

Ovary is the site of fertilization and pollination occurs externally

52.  Distinguish between a gamete and zygote. Explain their roles in sexual reproduction.
Solution

Gamete

Zygote

Formed after Meiosis

Formed by fusion of two gametes.

Gametes produces haploid number of chromosomes

Produces diploid number of chromosomes

Male and female parts produces gametes

Zygote formation takes place in female

Gametes are required for sexual reproduction

Zygote is the precursor for embryo formation


53. Draw the diagram of a flower and label the four whorls. Write the names of gamete producing organs in the flower.
Solution
Ovary produces female gametes whereas anthers produce male gametes

54. What is placenta? Mention its role during pregnancy?
Solution
A disc like structure embedded in the uterine wall is known as the placenta.
It contains villi on the embryo’s side of the tissue. There are blood spaces surrounding the villi on the mother’s side. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The embryo gets nutrition from the mother’s blood with the help of placenta. The waste generated by the developing embryo is removed by transferring it into the mother’s blood through the placenta.

55. What are various ways to avoid pregnancy? Elaborate any one method. Various ways to avoid pregnancy are given below
a) Physical barrier
b) Copper-T
c) Hormone Pills
d) Surgical procedure
Solution
Various ways to avoid pregnancy are as follows:
  • Physical barrier
  • Copper-T
  • Hormone Pills
  • Surgical procedure
Barrier method: Physical devices such as diaphragm (or cap) and condoms are used in this method. Diaphragm (or Cap) is used by females whereas condoms are used by males.

56. How does fertilisation take place? Fertilisation occurs once in a month. Comment.
Solution
One egg is released from either of the ovaries once in a month. From the ovaries the eggs get transferred to fallopian tube. The sperms swim towards the fallopian tube. At a time, only one sperm can penetrate the egg. This is known as fertilization. A menstrual cycle is composed of approximately 28 days. That is in one menstrual cycle only one egg is available for fertilization. Hence, it can be said that fertilization can occur only once in a month.

57. Reproduction is essentially a phenomenon that is not for survival of an individual but for the stability of a species. Justify.

Solution
The species would get extinct if there is no reproduction. Thus reproduction is linked to the population of a species. New individuals carries lineage of their parents. More number of organisms produced counter balances the mortality that arises due to various factors. In this way reproduction helps in maintaining the stability of a species

58. Describe sexually transmitted diseases and mention the ways to prevent them.
Solution
Sexually transmitted diseases are the diseases that get spread from person to person through sexual means. These include bacterial infections such as gonorrhoea and syphilis, and viral infections such as warts and HIV-AIDS. Few methods to prevent sexually transmitted diseases are:
  • Use of condoms or other physical barriers.
  • Avoiding sexual contacts with unknown partners.
  • Avoid sharing towels or underclothing.
  • Get a vaccination for hepatitis B.
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