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.

NCERT exercises

Exercises (11) Intext Questions (Page 114) (2) Intext Questions (Page 119) (5) Intext Questions (Page 126) (5)

NCERT Exemplar exercises

Multiple Choice Questions (27) Short Answer Questions (21) Long Answer Questions (10)

CBSE Class 10 Science previous year papers, with answers →

Questions · page 17 of 22

Q321 CBSE 2020
1. (a)What is vegetative propagation ? List three of its advantages. Name two methods employed to grow new plants through vegetative propagation.
2. (b)Explain, giving reason, why more complex organisms cannot give rise to new individuals through regeneration.
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Layering and grafting grow new plants from vegetative parts; complex organisms cannot regenerate because their specialised cells cannot rebuild all missing tissues.
(a) Vegetative propagation is a mode of asexual reproduction in which new plants develop from the vegetative parts of a plant, such as the root, stem or leaf, instead of from seeds. Advantages: (1) the plants bear flowers and fruits earlier than plants raised from seeds; (2) many plants identical to the parent, with all its characters, can be raised; (3) it is the only way to propagate plants that have lost the capacity to produce seeds, such as banana, orange, rose and jasmine. Methods: layering and grafting (cutting is another). (b) More complex organisms have a very high level of differentiation and organisation: specialised cells make up tissues, tissues make up organs and organs make up organ systems, each placed at a definite position in the body. Because their cells are so specialised, their tissues and organs have lost the ability to regenerate a whole body; a cut part contains only a few kinds of cells and cannot form all the other tissues and organs in their places. Hence they cannot give rise to new individuals from their cut body parts by regeneration.

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Q322 CBSE 2020
(a) Name the mode of reproduction of the following organisms and state the important feature of each mode :
1. (i)Planaria
2. (ii)Hydra
3. (iii)Rhizopus (b) We can develop new plants from the leaves of Bryophyllum. Comment. (c) List two advantages of vegetative propagation over other modes of reproduction.
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Planaria regenerates, Hydra buds, Rhizopus forms spores; Bryophyllum leaf buds grow into plants; vegetative propagation gives earlier flowering and parental characters.
(a) (i) Planaria reproduces by regeneration: when its body is cut into pieces, each piece grows into a complete organism, because specialised cells in it divide and develop into the lost parts. (ii) Hydra reproduces by budding: during favourable conditions a bud develops as an outgrowth by repeated cell division at one site on the parent, grows into a tiny complete individual on the parent's body, and then detaches as a new Hydra. (iii) Rhizopus reproduces by spore formation: its sporangia produce many spores, each covered by a thick wall that protects it through unfavourable conditions until it reaches a moist surface and grows into a new individual. (b) Bryophyllum reproduces by vegetative propagation through its leaves: buds are produced in the notches along the leaf margin, and when the leaf falls on moist soil, these buds develop into new plants. (c) Any two: (1) The new plants are genetically similar to the parent plant, so they have all its characteristics. (2) Plants raised by vegetative propagation bear flowers and fruits earlier than those produced from seeds. (3) Plants such as banana, orange, rose and jasmine, which have lost the capacity to produce seeds, can still be propagated. Other correct advantages also earn credit.

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Q323 CBSE 2019

Write the name and one function each of the parts A and B shown in the following diagram.

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A is the ovary, which produces eggs; B is the oviduct (fallopian tube), which carries the egg to the uterus.
A: Ovary. It produces the female gametes, the eggs (ova); it also secretes the hormones oestrogen and progesterone. B: Oviduct (fallopian tube). It carries the egg released by the ovary to the uterus, and fertilisation takes place in it.

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Q324 CBSE 2019

What are testes ? List two functions performed by testes in human beings.

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Testes are the male gonads, a pair of glands in the scrotum; they produce sperms and secrete testosterone.
Testes are the primary reproductive organs (gonads) of the human male: a pair of oval glands located in the scrotum, outside the abdominal cavity. Functions: (i) They produce the male germ cells, the sperms. (ii) They secrete the male sex hormone testosterone, which regulates the formation of sperms and brings about the changes seen in boys at puberty.

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Q325 CBSE 2019

What is multiple fission ? Draw a diagram to show multiple fission in Plasmodium.

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Multiple fission is the division of a single cell into many daughter cells at the same time, as in Plasmodium.
Multiple fission is a method of asexual reproduction in which a single-celled organism divides into many daughter cells at the same time: its nucleus divides repeatedly to form many nuclei, a little cytoplasm collects round each nucleus, and the parent cell then breaks to release the daughter cells, each of which grows into a new individual. Plasmodium (the malarial parasite) reproduces by multiple fission. Diagram, in four stages: parent cell with one nucleus; nucleus divides again and again, giving many nuclei; cytoplasm gathers round each nucleus, forming many daughter cells inside the parent; parent cell breaks and the daughter cells are set free.

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Q326 CBSE 2019

Distinguish between pollination and fertilisation. Mention the site and the product of fertilisation in a flower.

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Pollination is pollen reaching the stigma; fertilisation is the male germ cell fusing with the egg in the ovule, forming the zygote.
Pollination is the transfer of pollen grains from the anther (stamen) to the stigma of the same flower or of another flower. Fertilisation is the fusion of the male germ cell (from the pollen grain) with the female germ cell (egg) in the ovule. Pollination comes first and takes place on the stigma, outside the ovary, often with the help of agents such as wind, water or insects; fertilisation follows after a pollen tube has grown from the pollen grain through the style to the ovule, and takes place inside the ovule. Site of fertilisation: the ovule, inside the ovary. Product of fertilisation: the zygote.

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Q327 CBSE 2019

What is carpel ? Write the function of its various parts.

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The carpel is the female part of a flower: stigma receives pollen, style is the pollen tube's passage, ovary holds the ovules.
The carpel (pistil) is the female reproductive part of a flower. It has three parts: Stigma: the tip, often sticky; it receives the pollen grains. Style: the long middle part; it is the passage through which the pollen tube grows down to the ovary. Ovary: the swollen base; it contains the ovules with the egg cells (female gametes) and is the site of fertilisation. After fertilisation it develops into the fruit, and the ovules become seeds.

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Q328 CBSE 2019

How does the creation of variations in a species promote survival ? Explain with the help of an example.

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Variation lets some individuals survive a drastic change in surroundings, so the species survives; e.g. heat-resistant bacteria in warming water.
Variation means that the individuals of a species differ from one another; it arises during reproduction. Depending on the nature of their variations, different individuals have different kinds of advantages. If the surroundings (niche) of the species change drastically, the individuals whose variations suit the new conditions survive, reproduce and pass on those variations, while the others die. So the species is not wiped out: variation is useful for the survival of species over time. Example: Suppose a population of bacteria lives in temperate waters. If the water temperature rises because of global warming, most of the bacteria die, but a few variants that are resistant to heat survive and grow further. The species survives because of this variation. (Any other relevant example earns credit.)

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Q329 CBSE 2019
1. (a)Budding, fragmentation and regeneration, all are considered as asexual mode of reproduction. Why ?
2. (b)With the help of neat diagrams, explain the process of regeneration in Planaria.
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All three are asexual because one parent forms new individuals without gametes; each piece of a cut Planaria regrows into a complete individual.
(a) In budding, fragmentation and regeneration a new individual develops from a part of a single parent, without the formation and fusion of gametes; its cells arise by mitosis, so the offspring are almost identical copies of the parent. Reproduction by a single parent without gametes is asexual reproduction. (b) Regeneration in Planaria: when the body of a Planaria is cut into a number of pieces, each piece grows into a complete Planaria. Specialised cells in each piece proliferate to form a mass of cells; these cells then change into the different cell types and tissues in an organised sequence (development) and rebuild the missing parts, such as the head or the tail (see the diagram).

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Q330 CBSE 2019

Define pollination. Explain the different types of pollination. List two agents of pollination ? How does suitable pollination lead to fertilization ?

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Pollination is the transfer of pollen from anther to stigma; the pollen tube then carries the male germ cell to the egg, causing fertilisation.
Pollination is the transfer of pollen grains from the anther (stamen) to the stigma of a flower. Types of pollination: (1) Self-pollination: pollen is transferred from the anther to the stigma of the same flower. (2) Cross-pollination: pollen is transferred from the anther of one flower to the stigma of another flower. Two agents of pollination: wind and insects (water and other animals, such as birds, are also agents). When suitable pollen lands on the stigma, a pollen tube grows out of the pollen grain and travels through the style to reach the ovule in the ovary. The male germ cell carried in the tube fuses with the female germ cell in the ovule: this is fertilisation, and it forms the zygote.

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Q331 CBSE 2019
1. (a)What is reproduction ? List its two types.
2. (b)How are the modes of reproduction different in unicellular and multicellular organisms ?
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Reproduction makes new individuals of the same kind, asexually or sexually; unicellular organisms just divide, multicellular ones need specialised reproductive cells or organs.
(a) Reproduction is the process by which living organisms produce new individuals (young ones) of their own kind. Its two types are asexual reproduction and sexual reproduction. (b) Unicellular organisms reproduce by the division of their single cell - binary fission (Amoeba), multiple fission (Plasmodium) or budding (yeast): only one parent is required, it is a fast process, and no specialised reproductive cells are needed, as the whole cell divides. Multicellular organisms have bodies of cells organised into tissues and organs, so they cannot reproduce by simple cell division: sexual reproduction, common among them, requires two parents; reproduction is a slower process; and specialised reproductive cells, tissues or organs are needed - gametes formed in reproductive organs, or specialised cells and parts in asexual methods such as budding in Hydra, regeneration in Planaria and spore formation in Rhizopus.

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Q332 CBSE 2019
1. (a)Although Amoeba and Leishmania, both show same mode of reproduction, but the process of reproduction is carried out in different ways. Identify their mode of reproduction and mention the way it is carried out in the two species.
2. (b)What is regeneration ? Explain with the help of a diagram how this process is carried out in Planaria.
3. (c)Name the part of Rhizopus in which spores are formed. State the condition under which spores grow into a new individual.
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Amoeba and Leishmania divide by binary fission in different planes; Planaria pieces regenerate; Rhizopus spores form in sporangia and grow on moist surfaces.
(a) Both reproduce by binary fission, in which one cell divides into two. In Amoeba the cell can split in any plane. In Leishmania, which has a whip-like flagellum at one end, binary fission occurs in a definite orientation in relation to this structure (lengthwise). (b) Regeneration is the ability of a fully differentiated organism to give rise to new individuals from its body parts; it is carried out by specialised cells that multiply and develop into the various cell types and tissues. When a Planaria is cut into pieces, each piece regrows the missing parts and develops into a complete Planaria (see the diagram). (c) The spores of Rhizopus are formed in sporangia, the blob-like structures at the tips of the hyphae. The thick-walled spores grow into new individuals when they come in contact with a moist surface, such as moist bread.

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Q333 CBSE 2019
1. (a)Identify the given diagram. Name the parts 1 to 5.
2. (b)What is contraception? List three advantages of adopting contraceptive measures.
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The diagram shows the female reproductive system (fallopian tube, ovary, uterus, cervix, vagina); contraception prevents pregnancy, spaces births and controls population.
(a) The diagram shows the human female reproductive system. Parts: 1: Fallopian tube (oviduct); 2: Ovary; 3: Uterus; 4: Cervix; 5: Vagina. (b) Contraception is the prevention of pregnancy by using methods such as condoms, oral pills, a copper-T or surgery. Three advantages of adopting contraceptive measures: (1) a proper gap can be kept between two pregnancies, which protects the health of the mother; (2) unwanted pregnancies are avoided; (3) the population is kept under control. Other correct advantages, such as protection from sexually transmitted diseases by barrier methods, are also valid.

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Q334 CBSE 2019
1. (a)What are Sexually Transmitted Diseases (STD) ? List two viral and two bacterial STDs.
2. (b)What is contraception ? List three reasons for adopting contraceptive methods.
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STDs spread through sexual contact; contraception deliberately prevents pregnancy, to avoid unwanted pregnancies, space births and control the rise in population.
(a) Sexually transmitted diseases (STDs) are diseases that are transmitted from an infected person to a healthy person through sexual contact. Viral STDs: AIDS (caused by HIV) and warts. Bacterial STDs: gonorrhoea and syphilis. (b) Contraception is the deliberate prevention of pregnancy (of unwanted pregnancies) by using contraceptive methods. Reasons for adopting contraceptive methods: (1) to prevent unwanted pregnancies; (2) to keep a proper gap between successive births, for the better health of the mother; (3) to control the rise in population (birth rate). Preventing the transmission of STDs (by barrier methods) is also an accepted reason, as is any other correct one.

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Q335 CBSE 2019
1. (a)Name any two bacterial infections that are sexually transmitted. How can they be prevented ?
2. (b)List three different ways, other than the one stated in (a) above, that help an individual to avoid unwanted pregnancies. (c) List three advantages for adopting contraceptive measures.
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Gonorrhoea and syphilis are prevented by condoms; pills, Copper-T and surgery are other ways to avoid pregnancy; contraception spaces births and protects health.
(a) Gonorrhoea and syphilis. They can be prevented by using a condom (a covering for the penis, or a similar covering worn in the vagina) during sexual intercourse, and by avoiding sexual contact with an infected person or with many partners. (b) (i) Oral pills, which change the hormonal balance so that eggs are not released. (ii) A loop or copper-T placed in the uterus. (iii) Surgical methods: vasectomy, in which the vas deferens of the male is blocked so that sperm are not transferred, or tubectomy, in which the fallopian tube of the female is blocked so that the egg does not reach the uterus. (c) (i) They prevent unwanted pregnancies and help to keep the family small and the population in check. (ii) They allow proper spacing between children, which protects the health of the mother. (iii) Barrier methods also protect against sexually transmitted diseases such as gonorrhoea, syphilis and HIV-AIDS.

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Q336 CBSE 2019

What is sexual reproduction ? Explain how this mode of reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution ?

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Sexual reproduction combines the DNA of two parents, giving viable variations that asexual reproduction lacks; they help survival and drive evolution.
Sexual reproduction is the mode of reproduction in which two parents, a male and a female, produce gametes, and a male gamete fuses with a female gamete (fertilisation) to form a zygote, which develops into the new individual. More viable variation: the gametes are formed by meiosis and carry half the DNA, and at fertilisation the DNA of two different individuals is combined, so each offspring gets a new combination of characters, different from both parents. In asexual reproduction a single parent passes on copies of its own DNA, so the offspring differ only by rare DNA-copying errors and there is no mixing of characters. Since the combined variations come from healthy, living parents, they are viable. Effect on evolution: variations help some individuals survive changes in the environment; these individuals survive and reproduce more (natural selection), so useful variations accumulate over generations and can give rise to new species. By producing more variation, sexual reproduction promotes evolution.

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Q337 CBSE 2019
1. (a)Define vegetative propagation. List its two methods.
2. (b)Why is this mode practised for growing some types of plants ?
3. (c)Explain the process of budding in Hydra with the help of labelled diagrams.
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Vegetative propagation by layering or grafting suits plants that cannot form seeds; a Hydra bud grows tentacles and detaches as a new individual.
(a) Vegetative propagation is a mode of asexual reproduction in which new plants are produced from the vegetative parts of a plant (root, stem or leaves) without seeds. Two methods: layering and grafting. (Cutting is another; in nature roots, stems and leaves, such as the leaf buds of Bryophyllum, also give new plants.) (b) It is practised because (i) some plants, such as banana, orange, rose and jasmine, have lost the capacity to produce seeds, so they can be grown only in this way; (ii) it takes less time: such plants bear flowers and fruits earlier than those grown from seeds. Also, the new plants are genetically similar to the parent and keep all its characteristics. (c) Hydra reproduces by budding, using its regenerative cells. At one specific site on the body the cells divide repeatedly and form an outgrowth, the bud. The bud grows, develops a mouth and tentacles and becomes a tiny Hydra; when fully mature it detaches from the parent and lives as an independent individual. Labelled diagrams: parent Hydra with tentacles and basal disc, bud, growing bud with tentacles, detached new Hydra (see the figure).

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Q338 CBSE 2019
1. (a)Distinguish between cross-pollination and self-pollination. Mention the site and product of fertilization in a flower.
2. (b)Draw labelled diagram of a pistil showing the following parts : Stigma, Style, Ovary, Female germ cell
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Self-pollination stays within one flower, cross-pollination goes to another; fertilisation occurs in the ovule and produces the zygote.
(a) Self-pollination: pollen is transferred from the anther to the stigma of the same flower. Cross-pollination: pollen is transferred from the anther of one flower to the stigma of another flower of the same kind of plant, by agents such as wind, water or insects. Site of fertilisation: the ovary - inside the ovule, where the male germ cell brought by the pollen tube fuses with the female germ cell. Product of fertilisation: the zygote, which grows into the embryo inside the seed. (b) Labelled diagram of the pistil: the stigma at the top, the style below it, and the swollen ovary at the base holding an ovule with the female germ cell inside it (see the figure).

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Q339 CBSE 2019

What is contraception ? List its four different methods. State four reasons for adopting contraceptive methods.

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Contraception prevents pregnancy by barrier, chemical, IUCD or surgical methods, adopted to space children, protect the mother, keep families small and control population.
Contraception is the deliberate prevention of pregnancy (conception), using devices, chemicals or surgery, so that sexual intercourse does not lead to an unwanted pregnancy. Four methods: (i) mechanical barrier: condom; (ii) chemical: oral pills, which change the hormonal balance so that eggs are not released, or vaginal pills, which contain spermicides that kill sperms; (iii) intra-uterine contraceptive device (IUCD): loop or copper-T placed in the uterus; (iv) surgical: vasectomy (vas deferens blocked in the male) or tubectomy (fallopian tube blocked in the female). Four reasons: (i) to keep a gap between children; (ii) to protect the mother's health; (iii) to keep the family small and give it a better standard of living; (iv) to keep the population under control. (Barrier methods also prevent sexually transmitted diseases; any other relevant reason earns credit.)

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Q340 CBSE 2019
(a) Draw a diagram of human female reproductive system and label the parts :
1. (i)which produce an egg.
2. (ii)where fertilization takes place. (b) List two bacterial diseases which are transmitted sexually. (c) What are contraceptive devices ? Give two reasons for adopting contraceptive devices in humans.
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The ovary produces the egg and fertilisation occurs in the oviduct; gonorrhoea and syphilis are sexually transmitted bacterial diseases; contraceptive devices prevent pregnancy.
(a) Diagram of the human female reproductive system (see the figure), labelled: (i) Ovary - produces the egg. (ii) Oviduct (fallopian tube) - fertilisation takes place here. (b) Gonorrhoea and syphilis. (c) Contraceptive devices are the devices and methods used to prevent pregnancy, for example condoms (a mechanical barrier), oral pills (which change the hormonal balance) and the copper-T or loop placed in the uterus. Two reasons for adopting them (any two): to check population growth and keep the family small; to keep a gap between successive births; to maintain the reproductive health of the woman, since frequent pregnancies harm her health. Condoms also check the spread of sexually transmitted diseases.

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