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 8 of 22

1. Q141 CBSE 2025
   The ​part of a ​seed which is ​a ​source ​of ​food during its ​germination is :

   1. (a)Radicle
   2. (b)Cotyledon
   3. (c)Plumule
   4. (d)Embryo
   Show answer

   (b) Cotyledon

   Step-by-step solution →
2. Q142 CBSE 2025
   Vegetative propagation ​refers to the ​production ​of ​new ​plants of the same species ​from ​the following ​parts of a plant

   1. (a)stem, flower and fruit
   2. (b)roots, stem and flower
   3. (c)stem, leaves and flower
   4. (d)roots, stem and leaves
   Show answer

   (d) roots, stem and leaves

   Step-by-step solution →
3. Q143 CBSE 2025
   Question Nos. 17 ​to ​20 ​consists ​of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option ​from (a), (b), (c) and (d) ​given below ​:

   Assertion (A): The embryo gets nutrition from the mother's blood with the help of a special tissue called placenta.

   Reason (R): Placenta is a disc which is embedded in the uterine wall.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
   3. (c)Assertion (A) is true, but Reason (R) is false.
   4. (d)Assertion (A) is false, but Reason (R) is true.
   Show answer

   (b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).

   Step-by-step solution →
4. Q144 CBSE 2025
   Two statements are given ​below ​– one labelled as Assertion (A) ​and the ​other labelled as Reason (R). Select the correct answer to this question from ​the options (a), (b), (c) and ​(d) given ​below.

   Assertion (A): Variations are seen in offsprings produced by sexual reproduction.

   Reason (R): DNA copying in a reproducing cell is not completely accurate.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true, but Reason (R) is false.
   4. (d)Assertion (A) is false, but Reason (R) is true.
   Show answer

   (b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

   Step-by-step solution →
5. Q145 CBSE 2025
   Draw ​labelled diagrams ​to ​show ​different stages of budding in ​Hydra.
   Show answer

   Budding in Hydra is shown in four stages: a bud forms, grows, develops mouth and tentacles, then detaches as a new Hydra.

   Budding in Hydra is shown as a sequence of four labelled drawings. Stage 1: A small bud appears as a bulge on one side of the parent's body wall, formed by repeated cell division at that site. Stage 2: The bud enlarges while remaining attached to the parent. Stage 3: The bud develops its own mouth and tentacles and becomes a miniature Hydra. Stage 4: The fully formed bud detaches from the parent and grows into a new, independent Hydra; the parent is unharmed and can bud again. Labels required: parent Hydra, bud, tentacles, mouth, basal disc and new (daughter) Hydra.

   Step-by-step solution →
6. Q146 CBSE 2025
   Give reasons ​:

   1. (a)​The male reproductive organ responsible for formation of ​germ cells ​is located outside the abdominal cavity.
   2. (b)The roles of the glands, present along the path of the ​vas-deferens, are ​very ​significant.
   Show answer

   The testes hang outside the body because sperm formation needs a lower temperature; the glands' secretions carry and nourish the sperms.

   (a) The organ is the testis. Sperms are formed only at a temperature about 2 to 3 ${}^{\circ }$C below normal body temperature, and no site inside the abdominal cavity is that cool; the scrotum, hanging outside the cavity, provides the lower temperature, so the testes are located there. (b) The glands along the vas deferens are the seminal vesicles and the prostate gland. Their secretions form the fluid part of the semen: they provide the medium in which the sperms are carried, nourish them, and make their transport easier so that the sperms become motile - which is why their roles are very significant.

   Step-by-step solution →
7. Q147 CBSE 2025
   Write one function ​each of the ​following, in a ​seed ​:

   1. (i)Seed ​coat ​
   2. (ii)​Cotyledon
   3. (iii)Radicle
   4. (iv)Plumule
   Show answer

   The seed coat protects the embryo, the cotyledon stores food, the radicle forms the root and the plumule forms the shoot.

   (i) The seed coat is the tough outer covering that protects the embryo inside from mechanical injury, drying and micro-organisms; (ii) The cotyledon stores the food that nourishes the embryo and the young seedling until it can photosynthesise; (iii) The radicle is the embryonic root and grows downwards to form the root system, anchoring the plant and absorbing water and minerals; (iv) The plumule is the embryonic shoot and grows upwards to form the stem and the leaves.

   Step-by-step solution →
8. Q148 CBSE 2025
   Write the main steps ​to culture ​yeast ​in ​the laboratory.
   Show answer

   Dissolve sugar in water, add yeast, keep it warm for one to two hours, then observe a drop under a microscope.

   Dissolve some sugar in about $20$ mL of water in a clean beaker or test tube to make a dilute sugar solution; add a pinch of dry yeast granules and stir; put a cotton plug on the mouth of the vessel and keep it undisturbed in a warm place at about $25{}^{\circ }\text{C}$ to $30{}^{\circ }\text{C}$ for one to two hours, during which the yeast feeds on the sugar and multiplies; then place a drop of the culture on a clean glass slide, cover it with a cover slip and observe it under a microscope, where yeast cells with buds are seen.

   Step-by-step solution →
9. Q149 CBSE 2025
   1. (a)Define ​fertilisation.
   2. (b)​What ​happens ​to Zygote, Ovule, Ovary and Stamens after ​fertilisation in a ​flowering plant ?
   Show answer

   Fertilisation is the fusion of male gamete and egg; afterwards the zygote becomes the embryo, ovule the seed and ovary the fruit.

   (a) Fertilisation is the fusion of the male gamete, brought by the pollen tube, with the female gamete (egg cell) present in the ovule, to form a single cell called the zygote. (b) Zygote: it divides repeatedly and develops into the embryo of the seed. Ovule: its wall hardens into the seed coat and the whole ovule develops into the seed. Ovary: it grows and ripens to form the fruit, which encloses the seeds. Stamens: their work is over once pollen has been supplied, so they wither and fall off, as do the petals, sepals, style and stigma.

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10. Q150 CBSE 2025
    Differentiate between self-pollination and cross pollination. Which one ​of the two is ​better ​for the survival of ​species ? ​Give reason to justify ​your answer.
    Show answer

    Cross-pollination is better for survival: it brings more variation, so some individuals can survive changed surroundings, unlike self-pollination, which gives similar offspring.

    Self-pollination and cross-pollination differ as follows. Source of pollen: in self-pollination the pollen reaches the stigma of the same flower (or of another flower on the same plant); in cross-pollination it comes from a flower on another plant of the same species. Agent: self-pollination usually needs no outside agent; cross-pollination needs an agent such as insects, wind or water to carry the pollen. Pollen: self-pollination wastes little pollen; in cross-pollination much of the pollen can be lost on the way, so plants produce it in large amounts. Offspring: in self-pollination all the genes come from one parent plant, so the offspring vary little; cross-pollination combines the genes of two plants, so the offspring show more variation. Cross-pollination is better for the survival of the species. It produces more variation, and when the surroundings change (in temperature, water supply or disease, for example) some of the varied individuals are likely to suit the new conditions and survive, so the species continues; a population of nearly identical individuals could be wiped out by the same change.

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11. Q151 CBSE 2025
    Differentiate between ​a gamete ​and a zygote. State ​their significance in ​sexual ​reproduction.
    Show answer

    A gamete has half the chromosomes; the zygote, formed by fusion of two gametes, has the full number and starts the new individual.

    Differences: Gamete: a reproductive (germ) cell, the sperm or the egg; formed in the reproductive organs by a cell division that halves the chromosome number; has half the number of chromosomes and half the DNA of a body cell ($23$ in human beings); fuses with a gamete of the opposite sex. Zygote: the cell formed by the fusion of a male gamete and a female gamete at fertilisation; has the full number of chromosomes ($23+23=46$ in human beings), half from each parent; divides again and again to form the embryo. Significance: Gametes carry half the chromosomes, so their fusion restores the full number in the zygote and keeps the chromosome number and the DNA content constant from one generation to the next. The zygote is the first cell of the new individual and develops into the embryo; because it combines DNA from two parents, it brings a new combination of characters, that is, variation.

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12. Q152 CBSE 2025
    1. (i)Differentiate between self-pollination ​and ​cross-pollination.
    2. (ii)Explain the events taking place ​in a ​flower ​after a pollen lands on ​a suitable stigma, till fruit-formation.
    Show answer

    Self-pollination stays within one flower, cross-pollination goes between flowers; after fertilisation the ovule becomes the seed and the ovary the fruit.

    (i) Self-pollination is the transfer of pollen from the anther to the stigma of the same flower; it can take place without an outside agent, and the offspring vary less. Cross-pollination is the transfer of pollen from one flower to the stigma of another, by agents such as wind, water or animals; between flowers of different plants it combines germ-cells from two parents and gives more variation. (ii) The pollen grain germinates on the stigma and a pollen tube grows out of it, travels through the style and reaches the ovule in the ovary. The male germ-cell carried by the tube fuses with the female germ-cell in the ovule (fertilisation) to form a zygote. The zygote divides to form an embryo, the ovule develops a tough coat and becomes the seed, and the ovary grows and ripens into the fruit; the petals, sepals, stamens, style and stigma may shrivel and fall off.

    Step-by-step solution →
13. Q153 CBSE 2025
    1. (i)​What is the site of fertilisation of egg in a female reproductive tract ​?
    2. (ii)Fertilised ​egg on implantation in ​uterus lining continues ​to grow and develop to ​become a foetus. Explain how it ​gets nourishment and removes metabolic wastes during ​this period.
    Show answer

    Fertilisation occurs in the oviduct; the embryo gets glucose and oxygen and loses wastes through the placenta.

    (i) Fertilisation takes place in the oviduct (fallopian tube): the egg released by the ovary passes into the oviduct, and the sperms, travelling up through the cervix and the uterus, meet it there. (ii) After implantation the embryo is nourished through the placenta, a disc-like tissue embedded in the uterine wall. It has villi on the embryo's side and blood spaces of the mother around the villi, giving a large surface area. Glucose and oxygen pass from the mother's blood into the embryo's blood through the placenta, which nourishes it, and the wastes the embryo produces, such as carbon dioxide, pass the other way into the mother's blood, to be removed by her body.

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14. Q154 CBSE 2025
    (a) State in brief what ​happens ​when in ​a human female

    1. (i)an egg is not fertilised and
    2. (ii)fertilisation takes place. (b) List ​three ​techniques/devices used ​by human females to avoid pregnancy. Mention the ​side-effects ​caused by each method.
    Show answer

    An unfertilised egg leads to menstruation; fertilisation leads to an embryo nourished by the placenta; pills, Copper-T and tubectomy each have side effects.

    (a)(i) If the egg is not fertilised it lives for about a day and dies. The lining of the uterus, which had become thick and spongy and richly supplied with blood to receive a fertilised egg, is then no longer needed; it breaks down slowly and is shed through the vagina as blood and mucous. This is menstruation, which lasts about two to eight days and occurs about every month. (a)(ii) If fertilisation takes place, the zygote formed divides repeatedly into a ball of cells, the embryo, which travels down and is implanted in the thick lining of the uterus. It is nourished through the placenta, a special tissue with villi on the embryo's side and blood spaces on the mother's side, through which glucose and oxygen pass from the mother to the embryo and wastes are removed; the child develops for about nine months and is born by rhythmic contractions of the uterine muscles. (b) Three methods used by females: (1) Oral contraceptive pills, which change the hormonal balance so that eggs are not released; side effects are nausea, weight gain, headache and irregular menstrual bleeding. (2) An intra-uterine contraceptive device such as the Copper-T or loop placed in the uterus, which prevents implantation; side effects are irritation of the uterus, pain, excessive or irregular bleeding and risk of infection. (3) The surgical method tubectomy, in which the fallopian tubes are blocked so that the egg cannot meet the sperm; side effects are infection and inflammation if the operation is not done properly, and it is not easily reversed.

    Step-by-step solution →
15. Q155 CBSE 2025
    1. (i)​Write ​the functions of the ​following parts of human female reproductive system : (I) Ovary (II) ​Fallopian tube (III) Uterus
    2. (ii)State ​briefly two contraceptive methods used by ​human males.
    Show answer

    Ovary makes the ovum and hormones, fallopian tube is the site of fertilisation, uterus nourishes the foetus; condom and vasectomy are male methods.

    (i)(I) The ovary produces the female gametes, releasing one mature ovum about every month from puberty onwards, and it also secretes the female sex hormones oestrogen and progesterone, which bring about the secondary sexual characters and control the monthly changes in the uterine lining. (II) The fallopian tube (oviduct) collects the ovum from the ovary and carries it towards the uterus, and it is the site of fertilisation, where a sperm fuses with the ovum to form the zygote, which the tube then passes on to the uterus. (III) The uterus receives the embryo, whose implantation in its thickened lining begins pregnancy, and it nourishes and protects the developing embryo and foetus through the placenta until birth; if there is no fertilisation the lining is shed as menstruation. (ii) Two contraceptive methods used by human males are, first, the condom, a barrier method in which a thin sheath worn on the penis collects the semen so that the sperms are never deposited in the female reproductive tract, which also lowers the risk of sexually transmitted infections; and second, vasectomy, a surgical method in which a small portion of each vas deferens is cut out and the ends tied, so that sperms cannot pass from the testes into the semen and the semen released contains no sperms at all.

    Step-by-step solution →
16. Q156 CBSE 2025
    1. (i)​Identify the parts ‘X’ and ​‘Y’ in the figure given below ​:
    2. (ii)Name the yellowish ​coloured structures produced by the part labelled as ‘Y’.
    3. (iii)Write the name of the process by ​which these are transferred to the part ​labelled as ‘X’.
    4. (iv)​Explain the process of seed formation in a flowering plant.

    Show answer

    X is the stigma, Y the anther; pollen from Y reaches X by pollination, and fertilisation follows, turning the ovule into the seed.

    (i) ‘X’ is the stigma (the top of the pistil) and ‘Y’ is an anther (the swollen tip of a stamen). (ii) The yellowish structures produced by the anther are pollen grains. (iii) They are carried to the stigma by pollination. (iv) Seed formation: after pollination the pollen grain on the stigma germinates and grows a pollen tube down through the style until it reaches an ovule in the ovary. The male germ cell carried in the tube fuses with the egg inside the ovule — this is fertilisation — and a zygote is formed. The zygote divides repeatedly to form the embryo. The ovule then develops a tough coat around the embryo and becomes the seed, while the ovary grows and ripens into the fruit; the petals, sepals, stamens, style and stigma usually wither and fall off.

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17. Q157 CBSE 2025
    1. (i)List two roles of each ​of the ​following in human reproductive system : (I) Seminal vesicles ​and Prostate glands (II) Oviduct (III) ​Testis
    2. (ii)What ​happens in a human female when (I) fertilisation takes place, ​and ​(II) an egg is not ​fertilised ?
    Show answer

    Glands feed and carry sperms, the oviduct hosts fertilisation, the testis makes sperms and testosterone; fertilisation starts pregnancy, otherwise menstruation follows.

    (i)(I) Seminal vesicles and prostate glands: (1) their secretions are added to the sperms in the vas deferens and provide a fluid medium in which the sperms are transported — sperms plus these fluids make up the semen; (2) the secretion nourishes the sperms (it supplies fructose as an energy source) and, being alkaline, neutralises the acidity of the urethra and of the female tract so that the sperms remain alive and active. (II) Oviduct (fallopian tube): (1) it receives the ovum released by the ovary and carries it towards the uterus by ciliary action and muscular contraction; (2) it is the **site** where fertilisation takes place — the sperm meets and fuses with the egg here, and the oviduct then carries the zygote to the uterus. (III) Testis: (1) it produces the male gametes, the sperms; (2) it secretes the male sex hormone testosterone, which brings about the secondary sexual characters at puberty and regulates the formation of sperms. (ii)(I) When fertilisation takes place: the zygote formed in the oviduct divides to form a ball of cells, the embryo; the embryo travels to the uterus and is implanted in its thick, spongy lining; a placenta develops through which the embryo takes nutrition and oxygen from the mother's blood; the uterine lining is retained so menstruation stops; and the embryo develops into a foetus over about nine months, at the end of which the baby is born. (II) When an egg is not fertilised: the egg lives only about one day and then dies; the thick uterine lining prepared to receive it is no longer needed, so it breaks down and is shed through the vagina as blood and mucus — this is menstruation, which lasts about two to eight days and recurs about every twenty-eight days.

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18. Q158 CBSE 2025
    1. (i)​What is regeneration? Give one example ​of an organism ​that ​shows this process and one organism that does ​not. Why does ​regeneration not occur in the latter?
    2. (ii)Water in a pond appears dark ​green and contains filamentous structures. Name these structures and the method by which they reproduce. Explain the ​process.
    Show answer

    Regeneration occurs in Planaria but not in humans, whose cells are too specialised; the green pond filaments are Spirogyra, which reproduce by fragmentation.

    (i) Regeneration is the ability of a fully differentiated simple organism to grow a complete new individual from a piece of its body: if it is cut or broken into pieces, many of those pieces develop into separate whole organisms. It is carried out by specialised cells, which multiply and then change into the various cell types and tissues. Planaria (or Hydra) shows regeneration; a human being does not. Regeneration does not occur in a human being because the human body is highly differentiated: its cells are specialised for single functions and organised into interdependent tissues, organs and organ systems, so they can no longer divide freely and turn into every other cell type, and a fragment therefore cannot rebuild the missing organs or the whole body plan. (ii) The green filamentous structures are Spirogyra, a filamentous green alga. They reproduce by fragmentation, a form of asexual reproduction. On maturing, the filament simply breaks up into two or more fragments; each fragment then divides and grows into a new complete Spirogyra filament. Since the body is only a chain of similar cells with no division of labour, every piece can grow into a whole organism, and because a single parent is involved with no fusion of gametes the new filaments are identical to the parent.

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19. Q159 CBSE 2025
    1. (a)Define Puberty. List any two changes ​seen in boys ​at the time of ​puberty.
    2. (b)Why are testes in ​human males located outside the abdominal cavity in scrotum ?
    3. (c)List any three techniques of contraception used by ​humans. Which one of these is not meant ​for ​males ?
    Show answer

    Puberty is when the reproductive organs mature; the scrotum keeps the testes cooler for sperm formation; oral pills are not meant for males.

    (a) Puberty is the period during adolescence at which the reproductive organs mature and become functional, so that the body becomes capable of sexual reproduction. Two changes seen in boys are the growth of thick hair on the face as a beard and moustache, and in the armpits and pubic region; and the cracking and deepening of the voice as the larynx enlarges. (b) The formation of sperms requires a temperature about two to three degrees Celsius below the normal body temperature. The scrotum, lying outside the abdominal cavity, is cooler than the interior of the body and so provides that lower temperature. (c) Three techniques are the barrier method, such as the condom; the chemical or hormonal method, that is oral contraceptive pills; and the surgical method, that is vasectomy in males or tubectomy in females. Of these, the oral contraceptive pill is not meant for males, since it is taken only by females.

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20. Q160 CBSE 2025
    Name the ​parts marked ​as ‘A’ and ‘B’ in the given diagram. Write in detail the ​changes ​that take ​place in a flower when the ​product of ‘B’ reaches ​‘A’ till a fruit is formed.

    Show answer

    A is the stigma, B the anther; after pollination and fertilisation the ovule becomes a seed and the ovary a fruit.

    A is the stigma and B is the anther. The product of the anther is pollen. (1) Pollination: pollen grains are carried from the anther to the stigma — within the same flower in self-pollination, from another flower in cross-pollination, by agents such as wind, water or animals. (2) On the stigma the pollen grain germinates: a pollen tube grows out of it and travels through the style to reach the ovule in the ovary, carrying the male germ-cell. (3) Fertilisation: in the ovule the male germ-cell fuses with the female germ-cell to form a zygote. (4) The zygote divides several times to form an embryo within the ovule. (5) The ovule develops a tough coat and is gradually converted into a seed. (6) The ovary grows rapidly and ripens to form the fruit, while the petals, sepals, stamens, style and stigma may shrivel and fall off.

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