Class 10 Science · Chapter 7

How do Organisms Reproduce?

434 Class 10 Science questions on How do Organisms Reproduce? from the NCERT textbook, NCERT Exemplar and CBSE board papers 2017–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 18 of 22

1. Q341 CBSE 2019
   List ​in proper ​sequence ​four ​steps of ​obtaining ​germinating dicot ​seeds.
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   Soak the seeds, then the radicle emerges, the cotyledons split, and finally the plumule emerges.

   (i) Soaking of the seeds: soak the dicot seeds (for example gram) in water overnight, then drain the excess water and keep them covered with a wet cloth so that they stay moist. (ii) Emergence of the radicle: after a day or so the seed coat bursts and the radicle (future root) comes out first. (iii) Splitting of the cotyledons: the swollen seed splits open and its two cotyledons separate. (iv) Emergence of the plumule: the plumule (future shoot) grows out from between the cotyledons.

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2. Q342 CBSE 2019
   A ​student wants ​to germinate dicot ​seeds. Write the four steps ​in ​correct sequence that will help him to perform the experiment in the ​right way.
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   Soak the seeds overnight, drain the water, keep them wrapped in wet cloth, and keep them warm and moist until they germinate.

   1. Soak a few healthy dicot seeds (gram, pea or bean) in water overnight. 2. The next day, drain off the excess water. 3. Wrap the seeds in a wet cotton cloth, or place them on wet cotton or blotting paper in a petri dish, and cover them. 4. Keep them in a warm place for two to three days, sprinkling water daily so that they stay moist but not under water. The seeds germinate: the radicle comes out first and then the plumule.

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3. Q343 CBSE 2019
   Draw a ​labelled diagram ​in proper ​sequence ​to ​show ​budding in hydra.
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   A bud forms on the parent Hydra, grows, develops tentacles and a mouth, and detaches as a new Hydra.

   Labelled diagram in sequence (see the figure): (1) Parent Hydra: a small bud appears as an outgrowth on the body wall, formed by repeated cell division at one site. (2) The bud grows larger. (3) The bud develops a mouth and tentacles at its free end and becomes a tiny Hydra, still attached to the parent. (4) The mature bud detaches from the parent and lives as a new, independent Hydra. Labels: bud, parent Hydra, tentacles, basal disc, new Hydra.

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4. Q344 CBSE 2019
   After examining a prepared slide under the high power ​of ​a compound microscope, a student ​concludes that ​the given slide shows the various stages of binary ​fission in ​a unicellular organism. Write two observations on the basis of which ​such ​a conclusion may be drawn.
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   The nucleus is seen elongated or divided into two, and a deepening constriction splits the cell into two nearly equal daughter cells.

   (i) The nucleus is seen elongated in some cells and divided into two nuclei in others - the nucleus divides first. (ii) A constriction appears in the cytoplasm (cell membrane) across the middle of the cell and deepens, dividing the cell into two nearly equal daughter cells, each with a nucleus.

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5. Q345 CBSE 2019
   List two ​observations on ​the ​basis of which it may be concluded ​that ​the given slide shows binary fission in Amoeba.
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   The nucleus is elongated or has divided into two, and a constriction across the middle divides the cell into two nearly equal halves.

   (1) The nucleus is elongated (dumb-bell shaped) and dividing into two, or two nuclei are seen in one cell. (2) A constriction appears in the cell membrane and cytoplasm across the middle of the cell, dividing it into two nearly equal halves, each with a nucleus.

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6. Q346 CBSE 2019
   Draw ​labelled diagram ​to show ​the following ​parts in ​an embryo ​of a ​pea seed : Cotyledon, Plumule, Radical
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   Draw the pea embryo with two cotyledons, the plumule between them and the radicle as the projecting pointed tip.

   Labelled diagram of the embryo of a pea seed (see the figure): two cotyledons (the seed leaves, which store food) are attached to a small embryo axis; the upper end of the axis is the plumule (the future shoot, with tiny leaves), lying between the cotyledons, and the lower end is the radicle (the future root, printed 'Radical'), a pointed tip that projects out of the seed.

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7. Q347 CBSE 2019
   A student observed a ​permanent slide showing asexual reproduction in Hydra. Draw labelled diagram in proper sequence of the observations ​that must have ​been ​made ​by the student. Name ​the ​process of reproduction also.
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   Budding: a bud forms on the parent Hydra, grows, develops tentacles and a mouth, then detaches as a new Hydra.

   Labelled diagrams in proper sequence (see the figure): (1) A small bud (outgrowth) appears on the side of the parent Hydra, formed by repeated cell division at one spot. (2) The bud grows larger. (3) It develops tentacles and a mouth and becomes a tiny Hydra, still attached to the parent. (4) It separates from the parent and lives as a new, independent Hydra. The process of reproduction is budding.

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8. Q348 CBSE 2018
   Write one main difference between ​asexual and sexual ​mode of ​reproduction. Which species is likely to have comparatively better ​chances ​of ​survival – the one reproducing ​asexually or the one reproducing sexually ? Give reason to justify your answer.
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   Sexual reproduction (two parents, gametes) gives more variation, so a sexually reproducing species is more likely to survive environmental change.

   Difference: in asexual reproduction only one parent is involved and no gametes are formed, whereas in sexual reproduction two parents (a male and a female) are involved, and male and female gametes are formed and fuse. The species reproducing sexually has comparatively better chances of survival. Reason: sexual reproduction combines DNA from two individuals and so generates more variation among the offspring. When the environment changes, some of these variants are likely to suit the new conditions; they survive and reproduce, so the species is not wiped out.

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9. Q349 CBSE 2018
   (a) Write the function of ​following parts in human ​female reproductive system ​:

   1. (i)Ovary ​
   2. (ii)​Oviduct ​
   3. (iii)Uterus (b) Describe in brief ​the structure and function of placenta.
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   The ovary releases the egg, the oviduct carries it, the uterus holds the developing embryo; the placenta exchanges food, oxygen and wastes.

   (a) (i) Ovary: produces and releases the egg (ovum), the female gamete, one egg every month; it also secretes female hormones such as oestrogen. (ii) Oviduct (fallopian tube): carries the egg from the ovary to the uterus; fertilisation takes place in the oviduct. (iii) Uterus: the fertilised egg is implanted in its thick, blood-rich lining, and the embryo develops there into a foetus. (b) Structure: the placenta is a disc embedded in the uterine wall. It has villi on the embryo's side, and blood spaces containing the mother's blood on the mother's side, which surround the villi and give a large surface area. Function: glucose and oxygen pass from the mother's blood to the embryo through the placenta, providing its nourishment, and the wastes of the embryo pass into the mother's blood to be removed.

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10. Q350 CBSE 2018
    1. (a)​What is variation ? How is variation ​created in a population ? ​How ​does the ​creation of ​variation in a species promote survival ?
    2. (b)Explain how, offspring and parents of organisms reproducing sexually have the same number ​of chromosomes.
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    Variation, from DNA-copying errors and sexual reproduction, helps a species survive change; halved gametes and fertilisation keep the chromosome number constant.

    (a) Variation is the occurrence of differences in the characters of the individuals of a species; offspring resemble their parents but are not identical to them or to one another. It is created in two ways: the copying of DNA during reproduction is not absolutely accurate, so small copying errors arise; and sexual reproduction combines the DNA of two parents, giving new combinations of variations. The variations accumulate over generations. If the surroundings change drastically, a population without variation could be wiped out, but individuals whose variations suit the new conditions survive and reproduce, so the species survives. For example, when the water they live in becomes much warmer, heat-resistant variants of bacteria survive while the others die. (b) The gametes (sperms and eggs) are formed by a special cell division that halves the chromosome number, so each gamete carries only one chromosome of each pair (23 in human beings instead of 46). At fertilisation a male and a female gamete fuse, so the zygote receives half from each parent and the original number is restored ($23+23=46$). Hence the offspring has the same number of chromosomes as its parents in every generation.

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11. Q351 CBSE 2018
    Describe in ​brief the ​role ​of the ​following parts in human male ​reproductive ​system ​:

    1. (i)Testis
    2. (ii)Seminal ​vesicle
    3. (iii)Vas deferens
    4. (iv)Urethra
    5. (v)Prostate glands
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    Testis makes sperms and testosterone, seminal vesicle and prostate add nourishing fluid, vas deferens carries sperms, and urethra is the common passage out.

    (i) Testis: produces the male gametes, the sperms, and secretes the male sex hormone testosterone (which regulates the formation of sperms and brings about the changes of puberty in boys). (ii) Seminal vesicle: secretes a fluid that forms part of the seminal fluid; it helps in the movement (mobility) of the sperms and also nourishes them. (iii) Vas deferens: carries (transports) the sperms formed in the testis to the urethra. (iv) Urethra: provides a common passage for both the sperms and the urine, and carries them out of the body through the penis. (v) Prostate gland: its secretion is added to the seminal fluid and provides nutrition to the sperms (it also makes their transport easier).

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12. Q352 CBSE 2018
    What ​is Pollination ? How does ​it occur in ​plants ? ​Explain how ​pollination leads to ​fertilisation.
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    Pollination moves pollen from anther to stigma; the pollen tube carries the male germ cell to the ovule, where fertilisation forms the zygote.

    Pollination: the transfer of pollen grains from the anther of a stamen to the stigma of a carpel (pistil). How it occurs: in self-pollination the pollen reaches the stigma of the same flower; in cross-pollination the pollen is carried from one flower to the stigma of another flower by agents such as wind, water, insects and birds. How pollination leads to fertilisation: a pollen grain that lands on a suitable stigma germinates, and a pollen tube grows out of it. The tube grows down through the style into the ovary and reaches an ovule, carrying the male germ cell. In the ovule the male germ cell fuses with the female germ cell (egg); this fusion is fertilisation and forms the zygote. The zygote develops into the embryo, the ovule into the seed and the ovary into the fruit.

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13. Q353 CBSE 2018
    Draw diagrams ​showing ​reproduction in ​yeast ​in ​proper sequence.
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    Yeast reproduces by budding: a bud forms on the parent, receives a daughter nucleus, grows, and separates as a new cell.

    The diagrams are the four stages in the figure at step 4, in this order: (i) A mature parent yeast cell with a nucleus. (ii) A small outgrowth, the bud, appears on one side of the cell, and the nucleus divides into two. (iii) One daughter nucleus passes into the bud, which grows bigger. (iv) The bud separates from the parent as a new yeast cell, or stays attached and buds again, forming a chain of buds.

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14. Q354 CBSE 2018
    When ​a student observes a slide ​showing ​different stages of binary fission in ​Amoeba, he generally observes four stages of the ​process. Describe these stages in ​a proper sequence.
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    The rounded parent Amoeba divides its nucleus into two, a constriction forms between the nuclei, and the cell splits into two daughter Amoebae.

    (i) A single parent Amoeba with one nucleus; it withdraws its pseudopodia and becomes rounded. (ii) The nucleus elongates and divides into two daughter nuclei. (iii) A constriction appears in the cytoplasm (cell membrane) in the middle of the cell, between the two nuclei, and deepens. (iv) The cytoplasm divides at the constriction, forming two daughter Amoebae, each with one nucleus.

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15. Q355 CBSE 2018
    Name the process ​by which an ​amoeba ​reproduces. ​Draw the various ​stages ​of its reproduction ​in a proper ​sequence.
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    Amoeba reproduces by binary fission: the nucleus elongates and divides, then the cytoplasm constricts and splits into two daughter amoebae.

    Amoeba reproduces by binary fission (a kind of asexual reproduction). Stages, in sequence (diagram): (a) A mature amoeba with one nucleus. (b) The nucleus elongates and divides into two. (c) A constriction appears in the cytoplasm between the two nuclei and deepens. (d) The cell splits into two daughter amoebae, each with its own nucleus.

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16. Q356 CBSE 2018
    A student is ​viewing under ​a microscope ​a permanent slide ​showing various stages of asexual reproduction by budding ​in ​yeast. Draw diagrams of ​what he observes. (in ​proper sequence)
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    Budding in yeast is drawn in four stages: single cell, small bud, larger bud, and a chain of buds that separate.

    Diagrams of budding in yeast, in sequence: (a) A single yeast cell with a nucleus. (b) A small bud appears as an outgrowth on the cell; the nucleus divides and one nucleus passes into the bud. (c) The bud grows larger while still attached to the parent cell. (d) The bud forms another bud, giving a chain of buds; the buds finally separate and grow into new yeast cells.

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17. Q357 CBSE 2017
    Name the ​type of reproduction in which two individuals are formed ​from ​a single parent and the identity of the parent is lost. Write ​in brief about ​the ​first and ​the final stage of ​the process of this reproduction.
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    It is binary fission: the nucleus divides first, and finally the cytoplasm divides to give two daughter cells.

    Binary fission (for example, in Amoeba). First stage: the nucleus of the parent cell lengthens and divides into two nuclei. Final stage: the cytoplasm constricts between the two nuclei and divides, so the parent splits into two daughter cells, each with its own nucleus; the parent no longer exists as a separate individual.

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18. Q358 CBSE 2017
    Name ​a unicellular ​organism ​which ​reproduces by ​multiple ​fission.
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    Plasmodium, the malarial parasite, reproduces by multiple fission.

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19. Q359 CBSE 2017
    Name the method by which ​spirogyra ​reproduces ​under favourable ​conditions. Is ​this method ​sexual ​or asexual ?
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    Spirogyra reproduces by fragmentation, which is an asexual method.

    Under favourable conditions Spirogyra reproduces by fragmentation: the mature filament breaks up into small pieces (fragments), and each fragment grows into a new filament. The method is asexual, because only one parent is involved and no gametes are formed or fused.

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20. Q360 CBSE 2017
    How does ​Planaria ​reproduce. ​Is this ​method ​sexual ​or ​asexual ?
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    Planaria reproduces by regeneration, which is an asexual method.

    Planaria reproduces by regeneration: when its body breaks or is cut into pieces, each piece grows the missing parts and develops into a complete new Planaria. This method is asexual, because a single parent is involved and no gametes are formed or fused.

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