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 6 of 22

1. Q101 CBSE 2026
   “Variation ​is ​useful for the ​survival ​of species over time.” Explain ​this statement ​with the help of an example.
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   Variation lets some individuals survive a drastic change in their surroundings, so the species does not die out.

   Variation means that the individuals of a population differ slightly from one another. If the environment (niche) changes drastically, a population with no variation could be wiped out, but individuals with suitable variations may survive and reproduce, so the species continues. Example: if the water in which a population of bacteria lives becomes warmer, for instance because of global warming, most of the bacteria die, but the few heat-resistant variants survive and grow further. Variation is thus useful for the survival of species over time.

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2. Q102 CBSE 2026
   In a tobacco ​plant, the male gametes have twenty-four ​chromosomes. The number ​of chromosomes in the female gametes ​is also twenty-four. What ​is the number ​of chromosomes in the zygote produced ​? How is the ​chromosome number in the zygote re-established ?
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   The zygote has 48 chromosomes; gametes carry half (24) and fertilisation restores the full number.

   The zygote has $48$ chromosomes ($24$ from the male gamete $+24$ from the female gamete). The number is re-established because the gametes are produced by a special reduction division that halves the chromosome number of the parent plant from $48$ to $24$; when a male and a female gamete fuse at fertilisation the two half sets come together, so the zygote regains the full number of $48$ characteristic of the tobacco plant, and this halving-and-fusing keeps the chromosome number constant from generation to generation.

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3. Q103 CBSE 2026
   State two ​differences between pollination ​and ​fertilization.
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   Pollination transfers pollen to the stigma, whereas fertilisation fuses the male and female germ cells; pollination occurs only in plants.

   1. Pollination is the transfer of pollen grains from the anther to the stigma of a flower, whereas fertilisation is the fusion of the male germ cell with the female germ cell (egg) to form a zygote. 2. Pollination occurs only in plants, whereas fertilisation occurs in both plants and animals. Another acceptable difference: pollination takes place on the stigma, outside the ovary, and transfer between flowers needs agents such as wind, water or insects, whereas fertilisation takes place inside the ovule, after the pollen tube has carried the male germ cell there, and needs no outside agent.

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4. Q104 CBSE 2026
   Draw ​a diagram of ​the longitudinal section of a flower ​and label ​: ​Sepal, Petal, ​Ovary and Stigma.
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   The sepal is outermost, the petal inside it, and the central carpel has the ovary at its base and the stigma at its top.

   The diagram is a longitudinal section of a bisexual flower drawn on its stalk, with the four whorls in order from outside inward: the green Sepal at the base outside everything; the larger coloured Petal just inside it; a stamen on each side, made of a filament and a pollen-bearing anther; and the carpel in the centre, whose swollen base is the Ovary (drawn cut open to show the ovules inside), above which a slender style carries the broad sticky Stigma at the top. Leader lines mark Sepal, Petal and Stigma, each touching only the part it names, and Ovary is written inside the ovary itself. The labelled diagram is given in the figure.

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5. Q105 CBSE 2026
   Draw a neat diagram to show germination ​of pollen on the female reproductive part of the flower. ​Name and label only ​the following parts :

   1. (a)​The ​part that receives the pollen grain.
   2. (b)The structure ​that carries the male germ ​cell to reach the female germ ​cell.
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   The stigma receives the pollen grain, and the pollen tube carries the male germ cell down to the female germ cell in the ovule.

   (a) Stigma: the sticky top of the pistil, which receives the pollen grain. (b) Pollen tube: it grows out of the germinating pollen grain, down through the style, to the ovule, and carries the male germ cell to the female germ cell. The diagram shows the pistil (stigma, style and ovary with an ovule) with pollen grains on the stigma and a pollen tube growing from one of them down to the ovule; only Stigma and Pollen tube are labelled.

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6. Q106 CBSE 2026
   Following ​are the ​diagrammatic representations of different organisms performing ​a ​process. (i) Identify the organisms

   1. (a)and
   2. (b). (ii) Name the process ​commonly shown in both the figures. (iii) ​How is ​this process advantageous to the organisms ?

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   (a) Hydra and (b) Bryophyllum; both show asexual reproduction, which needs one parent and gives genetically identical offspring quickly.

   (i) (a) Hydra; (b) Bryophyllum (a leaf of Bryophyllum). (ii) Asexual reproduction: budding in (a) and vegetative propagation in (b). (iii) Only one parent is needed, so no mate has to be found and no gametes or fertilisation are involved; the process is quick and simple, so many offspring are produced in a short time, and every offspring is genetically identical to the parent, so characters that already suit the surroundings are passed on unchanged. Plants raised this way, as in (b), bear flowers and fruits earlier than plants grown from seed, and plants that have lost the capacity to produce seeds can still be multiplied.

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7. Q107 CBSE 2026
   (A) Name ​the reproductive ​and non-reproductive ​parts ​of ​bread mould (Rhizopus). (B) Give any two advantages of sexual reproduction in plants.
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   (A) Sporangia are reproductive, hyphae non-reproductive; (B) sexual reproduction gives variation and seeds that spread and survive.

   (A) The reproductive parts of bread mould are the tiny blob-on-a-stick structures: each is a sporangium — a knob-like case full of spores — borne on an erect stalk, and each spore it releases can grow into a new Rhizopus. The non-reproductive parts are the thread-like hyphae that make up the mycelium: the stolons that spread over the bread and the rhizoids that grow into it, which anchor the mould and absorb food from the bread. (B) Two advantages of sexual reproduction in plants are: (i) It produces variation. The offspring gets genes from two different parents, so it is not a copy of either; these variations help the species survive a changing environment and provide the raw material for evolution. (ii) It produces seeds. A seed carries the embryo with a store of food, can be dispersed by wind, water or animals so that new plants grow away from the parent, and can remain dormant through unfavourable conditions, then develop into a seedling when conditions are suitable.

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8. Q108 CBSE 2026
   State ​the two ​important ​roles of ​male ​sex ​hormone-testosterone.
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   Testosterone regulates the formation of sperms and brings about the changes seen in boys at puberty.

   Testosterone, the male sex hormone secreted by the testes, has these two important roles: (1) It regulates the formation of sperms. The tubules of the testes produce the male gametes, and testosterone controls and maintains that production, so sperms are formed only while the hormone is being secreted. (2) It brings about the changes in appearance seen in boys at the time of puberty, that is, the secondary sexual characters - growth of hair on the face and body, deepening of the voice, broadening of the shoulders and a more muscular build, and enlargement of the penis and the testes.

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9. Q109 CBSE 2026
   Give two ​reasons why secretions of ​prostate ​gland ​and seminal vesicles are of significance in human ​male reproductive ​system.
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   Their secretions form a fluid that makes transport of the sperms easier and also provides nutrition to the sperms.

   The prostate gland and the seminal vesicles add their secretions along the path of the vas deferens, and they matter for these two reasons: (1) The secretions provide a fluid in which the sperms are suspended, and this makes the transport of the sperms easier. Instead of remaining bare cells, the sperms can swim with their tails and be carried along the vas deferens and out through the urethra. (2) The same fluid provides nutrition to the sperms. A sperm is a small cell with a long tail and very little cytoplasm, so it carries almost no food of its own, and the nutrients in the fluid supply the energy it needs for the journey.

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10. Q110 CBSE 2026
    Give reasons for ​the ​following:

    1. (a)Adrenal gland is ​known as the stress gland of ​the body.
    2. (b)Prenatal ​sex determination ​is banned in India.
    3. (c)​Vegetative propagation is advantageous in ​some plants.
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    Adrenaline readies the body for stress; the ban stops female foeticide; vegetative propagation keeps the parent's characters and gives earlier flowering.

    (a) The adrenal glands, one above each kidney, secrete adrenaline straight into the blood whenever the body meets fear, anger or any other stressful situation. Adrenaline makes the heart beat faster so that more oxygen reaches the muscles, raises the breathing rate, and diverts blood from the skin and the digestive system to the skeletal muscles, thus preparing the body to fight or to run. Because it is the gland that readies the body to meet stress, it is called the stress or emergency gland. (b) The techniques were being misused for female foeticide, the selective abortion of female foetuses, which made the child sex ratio fall sharply and threatened the balance of the population. Prenatal sex determination is therefore prohibited by law in India, to stop female foeticide and to protect the girl child. (c) Because only a part of one parent plant is used and no gametes are involved, the new plants are genetically identical to the parent and keep all its desirable characters; plants that have lost the capacity to produce seeds, such as banana, orange, rose and jasmine, can be multiplied only in this way; and since the new plant begins from an already mature part, it bears flowers and fruit earlier than a plant grown from seed.

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11. Q111 CBSE 2026
    1. (a)How is the process of pollination ​different ​from fertilization ?
    2. (b)Where is ​the ​zygote ​located in the flower after fertilization ?
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    Pollination is pollen transfer to the stigma; fertilization is fusion of germ-cells in the ovule; the zygote lies in the ovule within the ovary.

    (a) Pollination is the transfer of pollen grains from the anther of a stamen to the stigma of a carpel, by agents such as wind, water or insects. Fertilization is the fusion of the male germ-cell, carried down the pollen tube, with the female germ-cell (egg) inside the ovule, forming a zygote. So pollination is a transfer of pollen that ends on the stigma and comes first, while fertilization is a fusion of germ-cells that takes place inside the ovule in the ovary, comes after pollination and produces the zygote. (b) After fertilization the zygote is located inside the ovule, within the ovary of the flower. It develops into the embryo, the ovule becomes the seed and the ovary becomes the fruit.

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12. Q112 CBSE 2026
    1. (a)​Which technique ​would you use for the propagation of ​varieties of grapes and roses ?
    2. (b)​Mention the parts of plants that can grow vegetatively.
    3. (c)State ​the ​role of pollen grains ​in ​a flower.
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    Grafting keeps a variety unchanged; root, stem and leaf can grow vegetatively; pollen grains carry the male gametes that fuse with the egg.

    (a) Grafting. Varieties of grapes and roses are propagated by grafting (layering is also used), an artificial method of vegetative propagation: a shoot cut from the chosen variety is joined onto a rooted plant and grows on as part of it. No gametes are involved, so the grafted shoot keeps every character of its parent and the variety is preserved. (b) The root, the stem and the leaf can grow vegetatively — for example the root of sweet potato and dahlia, the stem of potato, ginger and sugarcane, and the leaf of Bryophyllum, which bears buds in its notches. (c) Pollen grains are produced in the anther and carry the male gametes of the flower. After pollination a grain on the stigma germinates and grows a pollen tube down the style into the ovule, and the male gamete passes through this tube and fuses with the egg to bring about fertilisation, forming the zygote.

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13. Q113 CBSE 2026
    Given below are certain situations. ​Analyse each and ​describe its possible ​impact :

    1. (i)A population of bacteria ​living in temperate waters whose temperature increased by global warming.
    2. (ii)​The sperm ​encounters ​the egg when it reaches the oviduct in human females.
    3. (iii)Self pollination does not occur in a flower that contains only pistil.
    4. (iv)Egg does not get ​fertilised in a human female.
    5. (v)When the seed is placed under appropriate condition of water and air in the soil ?
    Show answer

    Heat-resistant bacteria survive, fertilisation leads to pregnancy, a pistil-only flower needs cross-pollination, an unfertilised egg causes menstruation, and a seed germinates.

    (i) Most of the bacteria would die in the warmer water, but a few variants that are resistant to heat would survive and multiply, so the species survives; this shows the importance of variation. (ii) Fertilisation occurs in the oviduct and a zygote is formed; it divides, gets implanted in the thick lining of the uterus and develops into an embryo, nourished through the placenta, so the woman becomes pregnant. (iii) The flower is unisexual (female) and has no pollen of its own, so it can be pollinated only by cross-pollination, with pollen brought from another flower by wind, water or animals; without that pollen no seeds or fruit form. (iv) The egg lives for about a day; the thick, blood-rich lining of the uterus is not needed, so it breaks down and comes out through the vagina as blood and mucus: menstruation, lasting about two to eight days. (v) The seed germinates: the embryo grows using food stored in the cotyledons, the radicle forms the root and the plumule the shoot, and a seedling develops.

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14. Q114 CBSE 2026
    1. (i)​Name an organ that helps ​in ​the formation of male germ cells in humans and also mention the condition that favours the formation of male germ cells.
    2. (ii)In male reproductive system, write ​the pathway followed to deliver ​male germ cells to the site of fertilisation.
    3. (iii)Mention the main physical feature of the ​male germ ​cell that helps it move towards the female ​germ cell.
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    The testes need a temperature below body temperature; sperms travel testis, vas deferens, urethra, vagina, uterus and oviduct, helped by the long tail.

    (i) Testes. Sperm formation needs a temperature lower than the normal body temperature, so the testes lie outside the abdominal cavity, in the scrotum, which is about $2$ to $2.5{}^{\circ }\text{C}$ cooler than the inside of the body. (The testes also secrete the hormone testosterone, which regulates the formation of sperms.) (ii) In the male reproductive system: Testis $\to$ vas deferens (sperm duct) $\to$ urethra, the common passage for urine and sperms, through the penis. Along the vas deferens the seminal vesicles and prostate gland add fluid that carries and nourishes the sperms. The sperms are deposited in the vagina and swim through the cervix and uterus to the oviduct (fallopian tube), where fertilisation takes place. (iii) The long tail of the sperm, which helps it swim towards the female germ cell.

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15. Q115 CBSE 2026
    Observe the given diagram and answer the ​questions ​that follow :

    1. (i)​Give ​the name of the structure and type of ​reproduction shown in the above diagram.
    2. (ii)State one advantage and one disadvantage of the above mentioned method of reproduction.
    3. (iii)Give reason : ​Asexual reproduction lacks genetic ​variation.
    4. (iv)Why have higher organisms resorted to sexual reproduction in spite of its complexity ?

    Show answer

    Bryophyllum leaf buds show vegetative propagation; asexual reproduction gives identical offspring, whereas sexual reproduction gives variation that helps survival and evolution.

    (i) The structure is the leaf of Bryophyllum, with adventitious buds in the notches of its margin; the type of reproduction is vegetative propagation, a form of asexual reproduction. (ii) Advantage: the new plants are genetically similar to the parent, so all its characters are kept, and many plants are raised quickly (they also flower and fruit earlier than plants grown from seeds). Disadvantage: the offspring show no variation, so they cannot adapt if the environment changes, and one disease can destroy all of them. (iii) Only one parent is involved and there is no fusion of gametes; each offspring receives a copy of the parent's DNA made during cell division, so apart from tiny copying errors it is genetically identical to the parent. (iv) Sexual reproduction combines DNA from two parents through gametes that each carry half the DNA, so every offspring has a new combination of characters. This variation helps the species survive changes in the environment and is the basis of evolution, which outweighs the complexity of the process.

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16. Q116 CBSE 2026
    (i) In an ​angiospermic flower, fertilization is said to take place when male gametes carried in the pollen tube fuse with the female gamete, present in the embryo sac. This results in lot of changes in different parts of the flower. State ​the changes taking place ​in ​the following structures of flower ​post ​fertilization :

    1. (a)Zygote
    2. (b)Ovule
    3. (c)Ovary
    4. (d)Sepals (ii) ​Define germination.
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    Zygote becomes embryo, ovule becomes seed, ovary becomes fruit and sepals fall off; germination turns the embryo into a seedling.

    (i)(a) Zygote: it divides repeatedly and develops into the embryo, which lies inside the ovule. (i)(b) Ovule: it develops a tough coat and is gradually converted into the seed, holding the embryo and its stored food. (i)(c) Ovary: it grows rapidly and ripens to form the fruit, whose wall encloses the seeds. (i)(d) Sepals: they usually shrivel and fall off, along with the petals, stamens, style and stigma; in some plants, such as brinjal, they stay attached to the fruit. (ii) Germination is the process in which the embryo inside a seed develops into a seedling under appropriate conditions of water, air (oxygen) and suitable temperature.

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17. Q117 CBSE 2026
    In flowering plants, the process of pollination leads to fertilization.

    1. (i)Explain with the help of a ​well-labelled diagram how the male ​germ cell from the pollen grain reaches the female germ cell ​located in the ovule.
    2. (ii)Differentiate between self-pollination and ​cross-pollination.
    3. (iii)Identify and name the ​parts ‘R’ ​and ‘S’ in ​the given diagram of ​seed.

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    Pollen tube carries the male germ cell to the egg; self-pollination is within a flower, cross-pollination between plants; R is plumule, S radicle.

    (i) Pollination brings the pollen grain to the stigma of the carpel, while the female germ cell lies inside an ovule in the ovary. The pollen grain that lands on a suitable stigma germinates and puts out a pollen tube, which grows through the tissue of the stigma and downward through the style until it reaches the ovary and enters the ovule. The male germ cell travels down this pollen tube and is released inside the ovule, where it fuses with the female germ cell, that is, with the egg. This fusion is fertilisation and it forms the zygote, which divides to form the embryo; the ovule then becomes the seed and the ovary becomes the fruit. The diagram should show the stigma with a germinating pollen grain, the pollen tube growing down the style with the male germ cell in it, the ovary, the ovule and the female germ cell inside it, all labelled. (ii) Self-pollination: pollen grains are transferred from the anther to the stigma of the same flower; cross-pollination: pollen grains are transferred from the anther of one flower to the stigma of a different flower, usually a flower on another plant of the same species. Self-pollination usually needs no outside agent; cross-pollination needs an agent such as wind, water, insects or birds. The progeny of self-pollination show little variation; cross-pollination between different plants brings together genes from two individuals, so its progeny show more variation. (iii) R is the plumule, the part of the embryo above the attachment of the cotyledons, which grows into the shoot; S is the radicle, the part below it, which grows into the root.

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18. Q118 CBSE 2026
    1. (i)Sugarcane and roses are ​mostly grown by vegetative ​propagation. Define this mode of reproduction.
    2. (ii)​List two advantages ​of vegetative ​propagation.
    3. (iii)Distinguish between unisexual and ​bisexual flowers. Give one example of ​each kind.
    Show answer

    Vegetative propagation raises plants from vegetative parts; its advantages are earlier flowering and seedless plants; unisexual flowers have one whorl, bisexual flowers both.

    (i) Vegetative propagation is the mode of **asexual** reproduction in plants in which new plants are produced from the vegetative parts of a plant — the root, stem, leaf or a bud — without the involvement of gametes, fertilisation or seeds. Since only one parent is involved, the new plants are genetically identical to it. (ii) Any two: plants raised in this way bear flowers and fruits **earlier** than those grown from seeds; plants such as banana, orange, rose and jasmine, which have lost the capacity to produce viable seeds, can still be grown; and every plant produced is genetically identical to the parent, so a desirable variety is preserved unchanged. (iii) A **unisexual** flower contains only one reproductive whorl — either the stamens or the pistil — so it can be cross-pollinated only; a **bisexual** flower contains both the stamens and the pistil in the same flower, so it may be self-pollinated as well. Example of a unisexual flower: papaya (also watermelon). Example of a bisexual flower: Hibiscus or China rose (also mustard).

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19. Q119 CBSE 2026
    Name ​the most suitable method of raising a banana plant. Is this ​mode ​of ​reproduction sexual or ​asexual ​? List ​any three advantages ​of growing plants by such a method.
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    A banana is raised by asexual vegetative propagation; advantages are earlier flowering and fruiting, propagation of seedless plants and offspring like the parent.

    Method: vegetative propagation. A banana plant is raised from a sucker - a young shoot that grows from the underground stem of an existing plant - because the cultivated banana has lost the capacity to produce seeds. Mode: asexual, because only one parent is involved and no gametes fuse. Three advantages: (1) plants raised this way bear flowers and fruits earlier than those grown from seeds; (2) plants that have lost the capacity to produce seeds, such as banana, orange, rose and jasmine, can still be propagated; (3) all the plants produced are genetically similar to the parent plant, so they keep all its desirable characteristics.

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20. Q120 CBSE 2026
    Given ​below are certain situations. Analyse and describe what would ​happen when :

    1. (i)Spores are liberated ​from ​blob-like structures of the bread mould?
    2. (ii)​Leaves of bryophyllum fall on wet ​soil ?
    3. (iii)A pollen from different species land on the stigma of totally unrelated species ​?
    4. (iv)Copper-T is placed in the uterus ​of a human female ?
    5. (v)Spirogyra breaks into smaller fragments upon maturation ?
    Show answer

    Spores, Bryophyllum buds and Spirogyra fragments each grow into new individuals; unrelated pollen fails to fertilise, and Copper-T prevents pregnancy.

    (i) The blob-like structures are sporangia; the spores released from them are carried by air, and on reaching a moist surface such as bread each spore germinates into a new bread mould (spore formation). (ii) Buds in the notches along the leaf margin develop roots and shoots and grow into new Bryophyllum plants (vegetative propagation). (iii) The pollen does not germinate, or its pollen tube does not grow down to the ovule, on the stigma of an unrelated species, so fertilisation does not occur and no seed forms. (iv) The copper-T, a contraceptive device, prevents pregnancy; it may cause side effects due to irritation of the uterus. (v) Each fragment grows into a new Spirogyra filament, a new individual (fragmentation).

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