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NCERT Exemplar · Class 10 Science How do Organisms Reproduce?

58 questions · 58 still being checked

Short Answer Questions 28–37 (part 4 of 6)

  1. Exercise 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.

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    NCERT’s answer
    The pistil is intact. Cross pollination has occurred leading to fertilisation and formation of fruit.
    Emasculation removes only the flower's own stamens; the carpel remains functional and receptive. Pollen from another flower is carried to the stigma by wind, insects or water, germinates and fertilises the ovule, so fruit still forms. Answer: Pollen reaching the stigma from a different flower (cross-pollination) fertilised it, so the emasculated flower still set fruit.

  2. Exercise 29

    Can you consider cell division as a type of reproduction in unicellular organism? Give one reason.

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    NCERT’s answer
    Yes, because it results in the formation of two daughter cells, that is, it results in the production of more individuals of the organism.
    Yes. In a unicellular organism the single cell is the whole organism, so when it divides (binary fission or budding) each daughter cell becomes a separate, complete new individual, directly increasing the number of organisms. Answer: Yes — the division of that one cell itself creates new individual organisms.

  3. Exercise 30

    What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?

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    NCERT’s answer
    Clone refers to offspring of an organism formed by asexual method of reproduction. Since they possess exact copies of the DNA of their parent, clones exhibit remarkable similarity.
    A clone is a group of genetically identical individuals produced from a single parent by asexual reproduction. Only mitosis is involved — no gametes fuse, so no genetic material from a second parent is added — and each offspring's DNA is simply a copy of the one parent's. Answer: Clone = genetically identical asexual offspring; the similarity follows from single-parent, mitotic copying with no gamete fusion.

  4. Exercise 31

    Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes?

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    NCERT’s answer
    Reduction division (meiosis) during gamete formation halves the chromosome 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.
    Meiosis halves the parent's chromosome number while forming gametes; fertilisation then fuses two gametes, restoring the full number in the zygote. \[\text{Parent}\;(2n) \xrightarrow{\text{meiosis}} \text{Gamete}\;(n) \] \[\text{Gamete (male)}\;(n) + \text{Gamete (female)}\;(n) \xrightarrow{\text{fertilisation}} \text{Zygote}\;(2n) \] Answer: Meiosis halves the chromosome number to \(\displaystyle n\) in each gamete; fusion of two such gametes restores \(\displaystyle 2n\) in the offspring, equal to each parent.

  5. Exercise 32

    Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this.

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    NCERT’s answer
    Sugar provides energy for sustaining all life activities in yeasts. In water, it fails to reproduce because of inadequate energy in its cells.
    Yeast reproduces by budding, which needs an energy and carbon source. Sugar solution supplies fermentable sugar for respiration and growth, while plain water offers no nutrients, so budding and multiplication cannot proceed in water. Answer: Sugar solution supplies the food yeast needs to bud and multiply; water does not.

  6. Exercise 33

    Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?

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    NCERT’s answer
    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.
    Bread-mould spores need moisture to absorb water, swell and germinate, and the growing hyphae need water to draw nutrients from the bread. A dry slice cannot supply this, so spores stay dormant and growth is poor. Answer: Moisture lets spores germinate and hyphae absorb nutrients from the bread; a dry slice lacks the water this needs.

  7. Exercise 34

    Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.

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    NCERT’s answer
    (a)
    Sexual reproduction involves two parents with different sets of characters
    (b)
    The gene combinations are different in gametes.
    (1)
    During meiosis, crossing over and independent assortment shuffle genes and chromosomes, giving each gamete a new combination. ($\displaystyle 2$) The zygote receives DNA from two different parents, so paternal and maternal traits combine differently in each offspring; occasional copying errors add further variation.
    Answer: Recombination during meiosis and the mixing of two parents' DNA at fertilisation together produce variation among sexually-reproduced offspring.

  8. Exercise 35

    Would a Planaria cut vertically into two halves regenerate into two individuals? Complete Figure 8.2\displaystyle 8.2 D and E by indicating the regenerated regions. NCERT_Question_Class10_Science_Exemplar_Ch8_Q35

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    NCERT’s answer
    Yes, shaded part in Figures D and E represent the regenerated halves. NCERT_Solution_Class10_Science_Exemplar_Ch8_Q35_ncert
    Yes — Planaria has very high regenerative power. Undifferentiated cells lying below the cut surface of each half divide and differentiate to regrow the missing side. So the single cut individual becomes two separate, complete Planaria, each identical in body plan to the original.Answer: Both halves regenerate their missing sides and grow into two independent Planaria.

  9. Exercise 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.

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    NCERT’s answer
    (a)
    No, there is no relationship between size of organism and its chromosome 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.
    \[2n:\ \text{fruit fly } 8,\ \text{housefly } 12,\ \text{human } 46,\ \text{chimpanzee } 48,\ \text{dog } 78 \]
    \[2n:\ \text{pea } 14,\ \text{onion } 16,\ \text{maize } 20,\ \text{rice } 24,\ \text{Ophioglossum} \approx 1260 \]
    (a)
    No — dog ($\displaystyle 78$) exceeds human ($\displaystyle 46$); a small fern has about $\displaystyle 1260$ against rice's 24.
    (b)
    No — reproduction follows the same pattern whatever the chromosome number.
    (c)
    Chromosomes are largely DNA:
    \[\text{chromosomes per cell}\uparrow \Rightarrow \text{DNA per cell}\uparrow,\qquad \text{cells}\uparrow \Rightarrow \text{total DNA}\uparrow \]
    Answer: (a) No. (b) No. (c) More chromosomes or more cells mean more DNA.

  10. Exercise 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?

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    NCERT’s answer
    Number of chromosomes in female gamete is $\displaystyle 24$ Number of chromosomes in zygote is $\displaystyle 48$
    Gametes of a species are haploid, so both male and female gametes of tobacco carry the same chromosome number. \[n_{\text{male gamete}} = n_{\text{female gamete}} = 24 \] Fertilisation restores the diploid number. \[2n_{\text{zygote}} = n_{\text{male}} + n_{\text{female}} = 24 + 24 = 48 \]Answer: Female gamete has $\displaystyle 24$ chromosomes; the zygote has 48.