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 1 of 10

1. Q1 NCERT · Exercises
   Asexual reproduction ​takes ​place ​through ​budding ​in

   1. (a)Amoeba.
   2. (b)Yeast.
   3. (c)Plasmodium.
   4. (d)Leishmania.
   Show answer

   (b) Yeast.

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2. Q2 NCERT · Intext Questions (Page 114)
   What ​is ​the importance ​of ​DNA copying ​in ​reproduction?
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   DNA copying passes the body design to offspring, keeping populations stable, and its inexact copying creates variation, the basis of evolution.

   DNA copying is important for two reasons. (i) It passes on the body design. The DNA in the nucleus is the information source for making proteins, and the proteins settle the body design of the organism. Before a cell divides it therefore builds a copy of its DNA, so that each new cell receives a complete blueprint and can build the same body design as the parent. This is what makes the offspring belong to the same species and is why reproduction gives stability to populations of a species. The copy is accompanied by the creation of an additional cellular apparatus, since a DNA copy pushed out on its own would have no cellular structure for maintaining life processes and would simply die. (ii) It produces variation. Copying is carried out by chemical reactions, and no bio-chemical reaction is absolutely reliable, so the copies are similar but not identical to the original. Very drastic changes kill the new cell, but milder ones survive, so the daughter cells are similar to yet subtly different from each other. This inbuilt tendency for variation during reproduction is the basis of evolution and it lets some members of a species survive when the niche changes.

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3. Q3 NCERT · Exercises
   Which ​of the following is ​not ​a part of the ​female ​reproductive system ​in human beings?

   1. (a)Ovary
   2. (b)Uterus
   3. (c)Vas deferens
   4. (d)Fallopian tube
   Show answer

   (c) Vas deferens

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4. Q4 NCERT · Intext Questions (Page 114)
   Why ​is variation beneficial ​to ​the ​species ​but not necessarily for the individual?
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   A variation seldom helps an individual in its usual surroundings, but when conditions change drastically, varied members may survive and keep the species going.

   Variation appears in a single individual, but survival is counted over a whole population. For the individual, a variation is usually of no advantage: in the conditions the population already lives in, the parent's body design works, so a difference from it brings nothing extra, and a drastic variation may even leave the new DNA copy unable to work with the cellular apparatus it inherits, so that the cell dies. For the species the picture is different, because niches change for reasons beyond the control of the organisms, such as a rise or fall in temperature, a change in water level or a meteorite hit. If a population of identical individuals suited to one niche were faced with a drastic change, every member would fail in the same way and the population could be wiped out. Because its members differ, there is some chance that a few of them can survive the new conditions and reproduce, so the species continues. The chapter's example makes the split plain: among bacteria living in temperate waters, resistance to heat does nothing for the few that carry it while the water is cool, but if global warming raises the temperature most of the bacteria die and only those heat-resistant variants survive and grow further. Variation is thus an insurance policy for the species, and most individuals pay the premium without ever collecting on it.

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5. Q5 NCERT · Exercises
   The anther contains

   1. (a)sepals.
   2. (b)ovules.
   3. (c)pistil.
   4. (d)pollen grains.
   Show answer

   (d) pollen grains.

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6. Q6 NCERT · Exercises
   What ​are ​the advantages of ​sexual ​reproduction ​over ​asexual reproduction?
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   Sexual reproduction gives more variation by combining two parents' DNA, helping a species survive changes in its niche and evolve into new species.

   Sexual reproduction has these advantages over asexual reproduction. (i) It combines the DNA of two different individuals, so each offspring receives one set of genes from each parent and carries a combination that neither parent had. (ii) It therefore produces far more variation than asexual reproduction, in which the offspring are near-identical copies of a single parent and the only variation comes from the small inaccuracies of DNA copying. (iii) That variation is what allows a species to survive a change in its niche: if a population were uniform, a drastic change such as a rise in temperature could destroy all of it, whereas in a varied population some individuals may happen to suit the new conditions and survive to rebuild it. (iv) Useful variations are inherited and accumulate over generations, so sexual reproduction speeds up adaptation and evolution and can give rise to new species. (v) The chromosome number is nevertheless kept constant, because each germ cell carries only half the usual number and the full number is restored at fertilisation — so the extra variation costs nothing in stability.

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7. Q7 NCERT · Exercises
   What are ​the ​functions performed ​by ​the ​testis in ​human beings?
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   The testis forms sperms and secretes testosterone, which regulates sperm formation and brings about male puberty changes.

   The testis performs two functions in human beings. (i) It produces the male germ cells, the sperms. Their formation begins at puberty; each sperm is a small cell consisting mainly of genetic material with a long tail that helps it move towards the female germ cell. The sperms are carried away by the vas deferens, which joins the urethra, and secretions of the seminal vesicles and the prostate gland provide them with a fluid that makes their transport easier and gives them nutrition. (ii) It secretes the male sex hormone testosterone into the blood. Testosterone regulates the formation of the sperms and brings about the changes in appearance seen at puberty in boys, such as thicker hair on the face and a deepening of the voice. The testes lie in the scrotum outside the abdominal cavity because sperm formation requires a temperature lower than that of the body.

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8. Q8 NCERT · Exercises
   Why does menstruation occur?
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   The uterine lining prepared each month for a fertilised egg breaks down and is shed when the egg is not fertilised.

   Menstruation occurs because the uterus prepares itself every month for a pregnancy that does not always follow. One of the ovaries releases an egg each month, and while that egg is travelling down the fallopian tube the lining of the uterus becomes thick and spongy and richly supplied with blood, so that it could receive a fertilised egg and nourish the embryo for months. If the egg is fertilised, the embryo settles in this lining and grows there, and the lining is not shed. If the egg is not fertilised, it lives only about a day, and the thick lining is then of no use. It therefore slowly breaks down and comes out through the vagina as blood and mucous. This is menstruation. It lasts about two to eight days, and because an egg is released every month the whole cycle repeats about every twenty-eight days.

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9. Q9 NCERT · Exercises
   Draw ​a labelled ​diagram of the longitudinal ​section ​of ​a ​flower.
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   Draw the flower cut lengthwise and label pedicel, receptacle, sepal, petal, stamen (filament, anther) and carpel (stigma, style, ovary, ovules).

   The labelled longitudinal section is drawn in the figure. Working from the outside inwards, the flower shows four whorls borne on the receptacle at the top of the pedicel (the stalk). (i) The sepals are the small green leaf-like structures of the outermost whorl, which protect the flower while it is in bud. (ii) The petals lie just inside them and are larger and brightly coloured, which attracts insects. (iii) The stamens are the male reproductive parts; each has a thin stalk called the filament carrying a swollen anther at its top, and the anther contains the pollen grains. (iv) The carpel, or pistil, stands at the centre and is the female reproductive part; it has a sticky stigma at the top on which pollen lands, a narrow style below it, and a swollen ovary at the base. Because the flower is cut lengthwise, the ovary is shown opened, revealing the ovules inside it. After fertilisation the ovule becomes the seed and the ovary becomes the fruit.

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10. Q10 NCERT · Exercises
    What ​are the ​different methods ​of ​contraception?
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    Contraception uses barrier methods, oral pills, intra-uterine devices (loop, copper-T) and surgical methods (vasectomy, tubectomy).

    The methods of contraception fall into four groups, according to the link in reproduction that each one breaks. (i) Barrier methods use a physical device to stop the sperm from reaching the egg — condoms used on the penis, and similar coverings for use in the vagina. These also protect both partners from sexually transmitted diseases such as gonorrhoea, syphilis and HIV-AIDS. (ii) Chemical methods: drugs taken orally by females, the oral pills, change the hormonal balance of the body so that eggs are not released and fertilisation cannot occur; they may have side effects. (iii) Intra-uterine contraceptive devices such as the loop or the copper-T are placed in the uterus to prevent pregnancy; they can cause side effects due to irritation of the uterus. (iv) Surgical methods block the duct itself: in a vasectomy the vas deferens in the male is blocked, so sperms cannot be transferred, and in a tubectomy the fallopian tube in the female is blocked, so the egg cannot reach the uterus. These are safe in the long run, though the surgery itself can cause infections and other problems if it is not done properly. The surgical removal of an unwanted pregnancy is not a method of contraception, since contraception acts before a pregnancy begins.

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11. Q11 NCERT · Exercises
    How ​are the ​modes ​for reproduction ​different in unicellular and multicellular ​organisms?
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    Unicellular organisms reproduce by dividing the whole cell; multicellular ones use body parts or, in complex forms, specialised germ cells.

    The difference follows from how the body is built. In a unicellular organism the whole body is a single cell, so dividing that cell already produces two complete organisms and no special reproductive structure is needed. The modes are therefore all forms of cell division: binary fission into two equal daughters (Amoeba, and Leishmania splitting along a definite axis), multiple fission into many daughters at once (Plasmodium), and budding, in which a bud on the parent cell grows and detaches (yeast). In a multicellular organism the cells are organised into specialised tissues and organs, so a cell taken from the body cannot by itself rebuild the whole organism and simple division will not do. Simpler multicellular organisms can still use body-based methods — fragmentation in Spirogyra, regeneration in Hydra and Planaria through specialised cells that grow into all the tissues, budding in Hydra, spore formation in Rhizopus, and vegetative propagation from a root, stem or leaf in plants such as sugarcane, roses and Bryophyllum. As the body design becomes more complex, reproduction is taken over by specialised reproductive tissue that makes germ cells; two germ cells fuse to form a zygote, and the zygote develops into the new individual. In short: a unicellular organism reproduces by dividing its whole body, whereas a multicellular organism reproduces through a part of its body set aside for the purpose.

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12. Q12 NCERT · Exercises
    How ​does ​reproduction help in ​providing stability to populations ​of species?
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    Reproduction replaces lost individuals, keeping numbers steady, and copies DNA with small variations, so some individuals survive when the niche changes.

    Populations of a species occupy well-defined places, or niches, in an ecosystem, and reproduction gives such populations stability in two ways. (i) It keeps the numbers steady. Individuals are constantly lost through age, disease and predation, and without reproduction the number in an area could only fall. By producing new individuals to replace those that die, reproduction keeps the size of the population consistent, at the level the food and conditions of the niche can support. (ii) It keeps the species suited to its place and able to survive change. Reproduction works by copying DNA, and the DNA carries the design of the body, so the offspring have essentially the same body design as their parents and can use the same niche. At the same time DNA copying is never absolutely accurate, so small variations appear in every generation. If a population were entirely uniform, a drastic change in the niche — a rise in temperature, the drying up of a pool, a new disease — could wipe out all of it at once. Because the population is varied, some individuals may happen to suit the new conditions; they survive, reproduce, and the population is rebuilt. So reproduction stabilises a population both in its numbers and in its continued existence over time.

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13. Q13 NCERT · Exercises
    What ​could ​be the ​reasons ​for adopting ​contraceptive ​methods?
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    To avoid unwanted pregnancy, protect the mother's health, prevent sexually transmitted diseases and control population growth.

    Contraceptive methods are adopted for reasons that reach from one couple outwards to the whole country. (i) To avoid an unwanted pregnancy. Being sexually mature does not mean a couple is ready, physically, emotionally or economically, to become parents, and contraception lets them decide whether and when to have a child. (ii) To space and limit pregnancies for the health of the mother. Pregnancy and childbirth make heavy demands on a woman's body, and pregnancies that follow closely on one another leave no time for recovery, so both her health and the care available to the children already born suffer. (iii) To protect against sexually transmitted diseases. Bacterial infections such as gonorrhoea and syphilis, and viral ones such as HIV-AIDS, are transmitted during sexual activity, and barrier methods such as condoms prevent this as well as preventing pregnancy. (iv) To control the growth of the population. The rate at which a population increases depends on the birth rate against the death rate; better health and living conditions have lowered the death rate, so a high birth rate makes the population rise rapidly and press on the country's food, land, water, housing and employment. Keeping the birth rate down is therefore necessary if the standard of living is to be maintained.

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14. Q14 NCERT · Intext Questions (Page 119)
    How does ​binary ​fission differ ​from ​multiple ​fission?
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    Binary fission splits the parent into two equal cells after one nuclear division; multiple fission gives many small cells after repeated nuclear divisions.

    The two differ in how many daughter cells are produced and in how the nucleus behaves before the cell splits. (i) Number of daughter cells: in binary fission the parent cell divides into two equal halves, so one parent gives exactly two daughter cells; in multiple fission the parent cell divides into many daughter cells simultaneously. (ii) Division of the nucleus: in binary fission the nucleus divides only once and the cytoplasm then divides; in multiple fission the nucleus divides again and again inside the parent cell while the cytoplasm stays undivided, and only afterwards does the cytoplasm divide around each nucleus. (iii) Size of the daughter cells: binary fission gives two comparatively large daughters, while multiple fission shares the parent among many, so each daughter cell is very small. (iv) Examples: binary fission is seen in Amoeba, where the splitting can take place in any plane, in Leishmania, where it occurs in a definite orientation in relation to the whip-like structure at one end of the cell, and in many bacteria and protozoa; multiple fission is seen in the malarial parasite Plasmodium.

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15. Q15 NCERT · Intext Questions (Page 119)
    How ​will an ​organism ​be ​benefited if it reproduces ​through ​spores?
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    Spores let an organism produce many offspring without a partner, spread them widely, and survive harsh conditions inside a thick wall.

    Reproducing through spores benefits the organism in three ways, one for each feature of a spore. (i) Numbers: a single sporangium contains a large number of spores and every one of them can develop into a new individual, so one parent starts very many offspring at once, and does so asexually, without needing a partner. (ii) Dispersal: spores are microscopic and light, so wind, water and animals carry them far away. New individuals therefore grow in fresh places and do not have to compete with the parent for food and space, which is how a mould that cannot move spreads from one slice of bread to another. (iii) Survival of bad conditions: each spore is covered by a thick wall, which protects it until it comes into contact with another moist surface, where it can begin to grow. The organism can therefore live through drought, heat and shortage of food in the resting spore stage instead of dying, and start growing again the moment conditions become favourable.

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16. Q16 NCERT · Intext Questions (Page 119)
    Can ​you think ​of ​reasons why more complex organisms ​cannot ​give rise to ​new ​individuals through regeneration?
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    Complex bodies are organised and their cells differentiated, so a cut piece cannot rebuild the rest; germ cells reproduce instead.

    Because a complex organism is not a random collection of cells and no piece of it carries what regeneration needs. (i) Its specialised cells are organised as tissues, its tissues into organs, and its organs have to lie at definite positions so that the organ systems work together. A piece cut from such a body holds only a fragment of this arrangement, with parts of some organs and none of others, so it cannot carry out digestion, respiration, circulation and excretion by itself and cannot stay alive. (ii) Its cells are fully differentiated for particular jobs and cannot start turning into other cell types. Regeneration in Hydra and Planaria is carried out by specialised cells that proliferate into a mass of cells from which the various cell types and tissues then arise in an organised sequence of development, and an ordinary piece of a complex body contains no such cells. (iii) Even in the animals that can regenerate, regeneration is not the same as reproduction, since no organism can depend on being cut up in order to reproduce. For all these reasons reproduction in complex organisms is made the function of one specific cell type, the germ cells produced in specialised reproductive organs, from which a new individual develops in the proper order from the beginning.

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17. Q17 NCERT · Intext Questions (Page 119)
    Why ​is vegetative ​propagation practised ​for ​growing some ​types ​of plants?
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    Plants flower and fruit earlier, seedless plants can be multiplied, and the parent's characteristics are kept unchanged.

    Vegetative propagation is practised because it gives a grower what raising the plant from seed cannot. (i) Plants raised by vegetative propagation bear flowers and fruits earlier than those produced from seeds, since they start from a piece of mature tissue instead of from a single fertilised cell, so the crop is ready sooner. (ii) It makes possible the propagation of plants that have lost the capacity to produce seeds, such as banana, orange, rose and jasmine; for these there is no other way of raising new plants at all. (iii) All the plants produced are genetically similar enough to the parent to have all its characteristics, so a chosen variety with a particular taste, colour or yield can be multiplied without change, which seeds could not guarantee. (iv) Only one parent plant is needed and methods such as layering and grafting are simple and cheap, so large numbers of plants of sugarcane, roses and grapes can be raised quickly for agricultural purposes.

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18. Q18 NCERT · Intext Questions (Page 119)
    Why ​is ​DNA ​copying ​an essential part ​of the ​process of ​reproduction?
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    DNA is the blueprint of body design, so each new cell needs its own complete copy to form a similar individual.

    Because a new individual cannot be built without its own complete set of instructions. Reproducing organisms create individuals that look very much like themselves, and they look alike because their body designs are alike; if the body designs are to be similar, the blueprints behind them must be similar. That blueprint is the DNA in the cell nucleus, which is the information source for making proteins, and different proteins would give an altered body design. The parent cell cannot simply hand over its own DNA, because it would then be left with none, so before dividing it uses chemical reactions to build a copy. This gives two complete sets, one for each of the two cells formed, and every new cell therefore starts life with the full instructions for making the parent's body design. Copying the DNA is also inseparable from the rest of cell division: keeping one copy and pushing the other out would fail, since the copy pushed out would have no organised cellular structure for maintaining life processes, so the copying is accompanied by the creation of an additional cellular apparatus and the two copies then separate, each with its own. This is why the creation of a DNA copy is called the basic event in reproduction. It also has a second consequence, that the copying is never perfectly accurate, and the resulting variations are the basis of evolution.

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19. Q19 NCERT · Intext Questions (Page 126)
    How ​is ​the process of pollination ​different from ​fertilisation?
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    Pollination moves pollen to the stigma, while fertilisation is fusion of male and female gametes inside the ovule, producing the zygote.

    They are two different stages of the same story, and they differ in four ways. (i) What happens: pollination is the transfer of pollen grains from the anther of the stamen to the stigma of the pistil, while fertilisation is the fusion of the male germ-cell produced by the pollen grain with the female gamete present in the ovule. (ii) Where it happens: pollination ends on the stigma, on the outside of the pistil, while fertilisation takes place inside the ovule, within the ovary. (iii) What it needs: pollination is brought about by external agents such as wind, water or animals, and is called self-pollination when the pollen stays in the same flower and cross-pollination when it goes from one flower to another; fertilisation needs no outside agent, only the pollen tube that grows out of the pollen grain and travels through the style to the ovary. (iv) What it produces: pollination produces nothing new, since nothing has joined, whereas fertilisation produces the zygote, which divides several times to form the embryo, so that the ovule becomes the seed and the ovary ripens into the fruit. Pollination always comes first, and it can happen without fertilisation following, but fertilisation in a flower cannot happen unless pollination has occurred.

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20. Q20 NCERT · Intext Questions (Page 126)
    What is ​the ​role of ​the ​seminal vesicles and ​the prostate ​gland?
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    Their secretions form a fluid that eases the transport of sperms and nourishes them; sperms plus this fluid form semen.

    The seminal vesicles and the prostate gland are accessory glands that lie along the path of the vas deferens and add their secretions to the sperms as the sperms pass. Their role is therefore twofold. (i) The secretions put the sperms into a fluid, which makes their transport out of the body much easier, since a sperm is only a tiny body of genetic material with a long tail and cannot travel through a dry tube. (ii) The same fluid provides the sperms with nutrition for the journey to the female germ-cell, which matters because a sperm carries no food store of its own. The sperms together with this fluid make up the semen. Neither gland produces the sperms themselves; sperms are formed in the testes, which also secrete the hormone testosterone.

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