Class 10 Science · Chapter 7

How do Organisms Reproduce?

185 Class 10 Science questions on How do Organisms Reproduce? from the NCERT textbook, NCERT Exemplar and CBSE board papers 2024–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 3 of 10

1. Q41 Exemplar · Multiple Choice Questions
   Which among the following ​statements ​are ​true for sexual reproduction in flowering ​plants?

   1. (i)It requires ​two ​types of gametes
   2. (ii)​Fertilisation is a compulsory event
   3. (iii)It ​always results in formation of zygote
   4. (iv)Offspring formed are clones

   1. (a)(i) and (iv)
   2. (b)(i), (ii) and (iv)
   3. (c)(i), (ii) and (iii)
   4. (d)(i), (ii) and (iv)
   Show answer

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

   Step-by-step solution →
2. Q42 Exemplar · Multiple Choice Questions
   In Figure 8.1, the parts ​A, ​B ​and ​C are ​sequentially

   1. (a)cotyledon, plumule and radicle
   2. (b)plumule, radicle and cotyledon
   3. (c)plumule, cotyledon and radicle
   4. (d)radicle, cotyledon and plumule
   Show answer

   (c) plumule, cotyledon and radicle

   Step-by-step solution →
3. Q43 Exemplar · Multiple Choice Questions
   Offspring ​formed as a result ​of ​sexual reproduction ​exhibit more ​variations ​because

   1. (a)sexual reproduction is a lengthy process
   2. (b)genetic material comes from two parents of the same species
   3. (c)genetic material comes from two parents of different species
   4. (d)genetic material comes from many parents
   Show answer

   (b) genetic material comes from two parents of the same species

   Step-by-step solution →
4. Q44 Exemplar · Multiple Choice Questions
   Reproduction is essential ​for ​living ​organisms in ​order to

   1. (a)keep the individual organism alive
   2. (b)fulfill their energy requirement
   3. (c)maintain growth
   4. (d)continue the species generation after generation
   Show answer

   (d) continue the species generation after generation

   Step-by-step solution →
5. Q45 Exemplar · Multiple Choice Questions
   During adolescence, several changes ​occur ​in the ​human body. ​Mark ​one change associated with sexual maturation ​in boys

   1. (a)loss of milk teeth
   2. (b)increase in height
   3. (c)cracking of voice
   4. (d)weight gain
   Show answer

   (c) cracking of voice

   Step-by-step solution →
6. Q46 Exemplar · Multiple Choice Questions
   In human ​females, an ​event that reflects onset ​of ​reproductive ​phase ​is

   1. (a)growth of body
   2. (b)changes in hair pattern
   3. (c)change in voice
   4. (d)menstruation
   Show answer

   (d) menstruation

   Step-by-step solution →
7. Q47 Exemplar · Multiple Choice Questions
   In ​human ​males, the testes lie ​in the ​scrotum, because ​it helps ​in the

   1. (a)process of mating
   2. (b)formation of sperm
   3. (c)easy transfer of gametes
   4. (d)all the above
   Show answer

   (b) formation of sperm

   Step-by-step solution →
8. Q48 Exemplar · Multiple Choice Questions
   Which among ​the following is not ​the function of testes ​at puberty?

   1. (i)formation of germ cells
   2. (ii)​secretion ​of testosterone
   3. (iii)development of ​placenta
   4. (iv)secretion ​of ​estrogen

   1. (a)(i) and (ii)
   2. (b)(ii) and (iii)
   3. (c)(iii) and (iv)
   4. (d)(i) and (iv)
   Show answer

   (c) (iii) and (iv)

   Step-by-step solution →
9. Q49 Exemplar · Multiple Choice Questions
   The ​correct ​sequence ​of ​organs in the male reproductive system for transport ​of sperms is

   1. (a)testis → vasdeferens → urethra
   2. (b)testis → ureter → urethra
   3. (c)testis → urethra → ureter
   4. (d)testis → vasdeferens → ureter
   Show answer

   (a) testis → vasdeferens → urethra

   Step-by-step solution →
10. Q50 Exemplar · Multiple Choice Questions
    Which ​among ​the ​following ​diseases is not sexually ​transmitted?

    1. (a)Syphillis
    2. (b)Hepatitis
    3. (c)HIV - AIDS
    4. (d)Gonorrhoea
    Show answer

    (b) Hepatitis

    Step-by-step solution →
11. Q51 Exemplar · Short Answer Questions
    In ​a bisexual ​flower ​inspite of the young stamens ​being removed artificially, the ​flower produces fruit. ​Provide a suitable explanation for the ​above situation.
    Show answer

    The pistil is intact, so cross-pollination by insects or wind, followed by fertilisation, lets the ovary ripen into fruit.

    The stamens are the male part, so removing them stops only self-pollination; the pistil was left untouched. Pollen carried from another flower by an insect or by the wind landed on the stigma, which is cross-pollination. A pollen tube then grew down the style and the male gamete fertilised the egg in the ovule, and the fertilised ovary ripened into the fruit.

    Step-by-step solution →
12. Q52 Exemplar · Short Answer Questions
    Can ​you consider ​cell ​division ​as a ​type of reproduction in unicellular ​organism? ​Give one reason.
    Show answer

    Yes, because a unicellular organism's whole body is one cell, so dividing produces two new individuals, as in Amoeba.

    Yes. In a unicellular organism the whole body is one cell, so when that cell divides the parent itself becomes two new individuals: an Amoeba dividing by binary fission gives two Amoebae. Cell division therefore produces new individuals of the same kind, which is what reproduction means.

    Step-by-step solution →
13. Q53 Exemplar · Short Answer Questions
    What ​is ​a clone? ​Why ​do ​offsprings formed by asexual reproduction exhibit ​remarkable similarity?
    Show answer

    A clone is a group of genetically identical individuals from one parent; asexual offspring are alike because mitosis copies the parent's DNA.

    A clone is a group of individuals that are morphologically and genetically identical to one another and to the single parent they came from. Offspring of asexual reproduction form such a clone because they are produced from one parent by mitotic divisions alone: no gametes are made and no fusion takes place, so the DNA handed on is a copy of the very same parental DNA. The only differences are the very small variations produced by occasional inaccuracies in DNA copying.

    Step-by-step solution →
14. Q54 Exemplar · Short Answer Questions
    Explain ​how, ​offspring and parents of ​organisms reproducing sexually ​have the same ​number of ​chromosomes?
    Show answer

    Meiosis halves the chromosome number in gametes and fertilisation doubles it again, so parents and offspring both have $2n=46$.

    Because the halving at gamete formation is exactly cancelled by the doubling at fertilisation. Germ cells of each parent divide by meiosis, which halves the number, so every gamete is haploid at $n=23$ against the parents’ $2n=46$. At fertilisation one male gamete fuses with one female gamete, so the zygote is diploid again at $23+23=46$. The zygote then divides only by mitosis, which copies the chromosomes exactly, so every body cell of the offspring carries the same $2n=46$ as the parents.

    Step-by-step solution →
15. Q55 Exemplar · Short Answer Questions
    Colonies ​of yeast fail to ​multiply ​in ​water, but ​multiply ​in sugar solution. Give ​one ​reason for this.
    Show answer

    Yeast cannot make its own food; water has no nutrients, whereas sugar solution gives it glucose for energy and growth, so it multiplies.

    Yeast is a saprophytic fungus and cannot make its own food, so it has to take in ready-made organic nutrients. Plain water supplies none, so with no source of energy or of carbon the cells can neither grow nor bud and the colony does not multiply. A sugar solution supplies glucose, which the yeast respires to release energy and uses as raw material for new cell material, so the cells bud and the colony multiplies.

    Step-by-step solution →
16. Q56 Exemplar · Short Answer Questions
    Why does bread mould ​grow ​profusely on a ​moist ​slice of bread ​rather than on a dry ​slice of bread?
    Show answer

    Moisture lets spores germinate and hyphae digest and absorb food, so mould grows profusely on moist bread, not dry bread.

    Bread mould, Rhizopus, is a saprophytic fungus. Its spores germinate only when moisture is present, and its hyphae feed by secreting digestive enzymes onto the bread and absorbing the digested food in solution, both of which need water. A moist slice supplies that water, so the spores germinate and the mycelium spreads profusely. A dry slice has too little water, so the spores stay dormant, the enzymes cannot act and nothing dissolves, and the mould hardly grows.

    Step-by-step solution →
17. Q57 Exemplar · Short Answer Questions
    Give two ​reasons ​for the ​appearance ​of variations ​among ​the ​progeny formed ​by sexual reproduction.
    Show answer

    Meiosis gives each gamete a different combination of genes, and chance fertilisation joins any male gamete with any female gamete.

    (i) Gametes are made by meiosis, in which the maternal and paternal chromosomes exchange segments (crossing over) and are then assorted into the gametes independently of one another, so every gamete carries a different combination of the parent’s genes. (ii) Fertilisation is a chance event between two different parents: any one of the many genetically different male gametes may fuse with any one of the female gametes, so each zygote receives a fresh combination of DNA, half from each parent.

    Step-by-step solution →
18. Q58 Exemplar · Short Answer Questions
    Would ​a ​Planaria cut ​vertically ​into two halves regenerate into ​two individuals? Complete Figure 8.2 D ​and E ​by indicating the regenerated ​regions.

    Show answer

    Yes; each half regenerates the missing half from dividing cells, so one Planaria gives two whole individuals.

    Yes. Planaria has a very high power of regeneration because its body carries large numbers of unspecialised, actively dividing cells. A vertical cut leaves each half with part of the head and one eyespot, half the pharynx and part of every organ system, along with those cells. A mass of dividing cells forms over each cut surface and grows into the missing half, so each half becomes a complete worm and one animal gives two individuals. In the figure, D and E are completed by drawing in the missing half of each animal, the second eyespot and the other half of the pharynx and the body, so that D and E become two whole Planaria.

    Step-by-step solution →
19. Q59 Exemplar · Short Answer Questions
    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.

    1. (a)Do larger ​organisms have more number ​of chromosomes/cells?
    2. (b)Can organism with fewer chromosomes reproduce more ​easily than organisms with more number of chromosomes?
    3. (c)More the number of chromosomes/cells greater is the DNA content. Justify.
    Show answer

    Larger organisms do not have more chromosomes and fewer chromosomes do not ease reproduction; more chromosomes mean more DNA only within a species.

    (a) No. There is no correlation between body size and chromosome number. Among animals the fruit fly has $2n=8$, the frog $26$, the human $46$, the elephant $56$ and the much smaller dog $78$; among plants pea has $14$, onion $16$, maize $20$, rice $24$ and potato $48$. The dog is far smaller than the elephant yet carries more chromosomes. (b) No. How easily an organism reproduces depends on its mode of reproduction, its generation time, the age at which it matures and the number of gametes and offspring it produces, not on its chromosome number. All the homologous pairs are dealt with together in one meiosis, so extra pairs do not slow it. (c) The statement holds only within one species. DNA is carried on the chromosomes, so for cells of the same species more chromosomes does mean more DNA: a human body cell with $46$ holds twice the DNA of a gamete with $23$. Across species it fails, because chromosomes differ enormously in size — a lily has $24$ very long chromosomes while the small fern Ophioglossum reticulatum has over $1200$ short ones. So it is justified as a comparison of ploidy within a species, not as a general rule.

    Step-by-step solution →
20. Q60 Exemplar · Short Answer Questions
    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?
    Show answer

    The female gamete has 24 chromosomes and the zygote has $24+24=48$ chromosomes.

    The female gamete also has $24$ chromosomes, because both gametes of a species are haploid. The zygote has $24+24=48$ chromosomes, the diploid number of the tobacco plant.

    Step-by-step solution →