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 16 of 22

Q301 CBSE 2020

What is pollination ? Name any two agents of pollination. How does pollination lead to fertilisation ?

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Wind or insects carry pollen to the stigma; the pollen tube then takes the male germ cell to the egg, forming the zygote.
Pollination is the transfer of pollen grains from the anther of a stamen to the stigma of a flower, either of the same flower or of another flower. Two agents of pollination: wind and insects (water, birds and other animals are also agents). After a pollen grain lands on the stigma, a pollen tube grows out of it and travels through the style to reach the ovule in the ovary. The male germ cell passes down the tube and fuses with the female germ cell (egg) in the ovule. This fusion is fertilisation, and it forms the zygote.

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Q302 CBSE 2020
(a) Give one function of each of the following parts in a flower :
1. (i)Ovary
2. (ii)Stigma
3. (iii)Anther (b) Name any three parts of a flower which may fall off after fertilisation.
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Ovary holds ovules and becomes the fruit; stigma receives pollen; anther makes pollen; petals, sepals and stamens may fall off.
(a) (i) Ovary: contains the ovules with the female germ cells, where fertilisation takes place; after fertilisation it develops into the fruit. (ii) Stigma: receives the pollen grains during pollination. (iii) Anther: produces the pollen grains, which contain the male germ cells. (b) Petals, sepals and stamens (the style and the stigma may also fall off).

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Q303 CBSE 2020

What is placenta ? List its two roles during pregnancy.

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The placenta is a disc-shaped tissue in the uterine wall that brings nutrition and oxygen to the embryo and removes its wastes.
The placenta is a special disc-shaped tissue embedded in the uterine wall which connects the embryo to the mother. It has villi on the embryo's side, surrounded by blood spaces on the mother's side. Two roles during pregnancy: 1. It provides nutrition (glucose) and oxygen from the mother's blood to the embryo. 2. It removes the waste substances produced by the embryo by transferring them into the mother's blood.

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Q304 CBSE 2020

Define the term variation. Why is variation beneficial to a species ? List two reasons for the appearance of variations among the progeny formed by sexual reproduction.

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Variation means differences among individuals of a species; it helps the species survive when its environment changes.
Variation is the occurrence of differences in characters (structure and function) among the individuals of the same species, including the differences between offspring and their parents. Variation is beneficial to a species because it helps the species survive a change in its environment: when conditions change, for example when the water in which bacteria live becomes too hot, most individuals may die, but the variants suited to the new conditions survive and reproduce, so the species is not wiped out. Variation is also the basis of adaptation and evolution. Two reasons for variations among the progeny of sexual reproduction: (i) small errors (inaccuracies) in copying the DNA when germ cells are formed; (ii) the combination of DNA from two different parents at fertilisation, which gives each offspring a new combination of characters. Mutations (changes in DNA) are also accepted as a reason.

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Q305 CBSE 2020

Name the most suitable method of raising a banana plant. Is this mode of reproduction sexual or asexual ? List three advantages of growing plants by such a method.

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Banana is raised by vegetative propagation, which is asexual; it propagates seedless plants, gives earlier flowering and fruiting, and preserves the parent's characters.
Method: vegetative propagation. A banana plant is raised from a sucker, a shoot that grows from a bud on the underground stem of a parent plant (it can also be raised by tissue culture). Mode: asexual, since only one parent is involved and no gametes are formed. Advantages: (i) Plants such as banana, which have lost the capacity to produce seeds, can be propagated; (ii) The new plants bear flowers and fruits earlier than plants raised from seeds; (iii) All the new plants are genetically similar to the parent plant, so its desirable characters are preserved.

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Q306 CBSE 2020

What are sexually transmitted diseases ? Name one sexually transmitted disease each, caused by a virus and a bacterium. List two benefits of using mechanical barriers during the sexual act.

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STDs spread through sexual contact; AIDS (virus) and gonorrhoea (bacterium) are examples; condoms prevent pregnancy and help prevent STDs.
Sexually transmitted diseases (STDs) are infections that spread from an infected person to a partner through sexual contact. Caused by a virus: AIDS, caused by HIV (warts is another example). Caused by a bacterium: gonorrhoea (syphilis is another example). Benefits of mechanical barriers such as condoms: (1) the sperm cannot reach the egg, so unwanted pregnancy is prevented; (2) the exchange of body fluids is blocked, which helps to prevent the transmission of many STDs, such as HIV-AIDS and gonorrhoea.

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Q307 CBSE 2020

Name the process of reproduction observed in yeast. Design an activity to observe this mode of reproduction in a school laboratory. Name one more organism which reproduces by this mode.

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Yeast reproduces by budding: observe a warm sugar-yeast culture under a microscope for buds; Hydra also reproduces by budding.
Process: budding. Activity: dissolve about $10$ g of sugar in $100$ mL of water, take $20$ mL of this solution in a test tube and add a pinch of yeast granules. Put a cotton plug on the mouth of the test tube and keep it in a warm place. After $1$ to $2$ hours, put a small drop of the yeast culture on a slide, cover it with a coverslip and observe it under a microscope: many yeast cells show small outgrowths (buds), and some buds carry buds of their own. Another organism that reproduces by budding: Hydra.

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Q308 CBSE 2020

Name the type of asexual reproduction in which two individuals are formed from a single parent and the parental identity is lost. Draw the initial and final stages of this type of reproduction. Write the event with which this process starts and draw its labelled diagram.

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The process is binary fission, as in Amoeba, which starts with division of the nucleus (karyokinesis) followed by division of the cytoplasm.
The process is binary fission, as in Amoeba. Initial stage: one parent Amoeba with a single nucleus; final stage: two daughter Amoebae, each with its own nucleus, and the parent no longer exists. The process starts with the division of the nucleus (karyokinesis): the nucleus elongates and splits into two, and then the cytoplasm divides. The stages, with the dividing nucleus labelled, are drawn in the figure.

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Q309 CBSE 2020
1. (a)List two reasons of using contraceptive methods by married couples.
2. (b)Write in proper sequence the processes going on in the different organs of the reproductive system of a human female starting from the time of egg production to childbirth.
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Contraceptives prevent unwanted pregnancy; the egg forms in the ovary, is fertilised in the oviduct, and the embryo grows in the uterus until birth.
(a) Any two of these: to prevent unwanted pregnancies, so that the couple decides when to have a child and how many children to have; to keep a gap between children, so that the mother's health is not harmed by frequent pregnancies; to prevent sexually transmitted diseases, by using barrier methods such as the condom. (b) The processes in order: 1. Ovary: an egg is produced (matures) and is released, one egg each month. 2. Oviduct (fallopian tube): the egg is carried from the ovary into the oviduct. 3. Oviduct: sperms reach the egg and fertilisation takes place, forming the zygote. 4. Uterus: the zygote divides to form an embryo, which is implanted in the thick lining of the uterus. 5. Uterus: the embryo, nourished through the placenta, grows and develops into a foetus. 6. Uterus, cervix and vagina: after about nine months the uterine muscles contract rhythmically and the baby is delivered through the vagina (childbirth).

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Q310 CBSE 2020
(a) Identify the modes of asexual reproduction in each of the following organisms :
1. (i)Hydra
2. (ii)Planaria
3. (iii)Amoeba
4. (iv)Spirogyra
5. (v)Rhizopus (b) List three advantages of vegetative propagation. (c) Why can fertilisation not take place in flowers if pollination does not occur ?
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Hydra buds, Planaria regenerates, Amoeba divides by binary fission, Spirogyra fragments and Rhizopus forms spores; without pollination no pollen tube forms, so no fertilisation.
(a) (i) Hydra: budding; (ii) Planaria: regeneration; (iii) Amoeba: binary fission; (iv) Spirogyra: fragmentation; (v) Rhizopus: spore formation. (b) Plants that have lost the capacity to produce seeds, such as banana, orange, rose and jasmine, can be grown by vegetative propagation; all the new plants are genetically similar to the parent plant and keep all its characteristics; plants raised this way bear flowers and fruits earlier than plants grown from seeds. (c) Fertilisation is the fusion of the male germ cell, produced by the pollen grain, with the female germ cell (egg) inside the ovule. The male germ cell can reach the egg only through a pollen tube, which grows from a pollen grain that has landed on the stigma and travels down the style to the ovule. If pollination does not occur, no pollen grain reaches the stigma, so no pollen tube forms, the male germ cell never reaches the egg, and fertilisation cannot take place.

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Q311 CBSE 2020
1. (a)List three different categories of contraception methods.
2. (b)Why has Government of India prohibited prenatal sex determination by law ? State its benefits in the long run.
3. (c)Unsafe sexual act can lead to various infections. Name two bacterial and two viral infections caused due to unsafe sex.
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Contraception is barrier, chemical or surgical; prenatal sex determination is banned to stop female foeticide; gonorrhoea and syphilis are bacterial, warts and HIV-AIDS viral.
(a) The three categories are barrier methods (for example, the condom, which keeps sperms from reaching the egg); chemical methods (oral pills, which change the hormonal balance so that no egg is released, and vaginal pills or creams, which kill sperms); and surgical methods (vasectomy, in which the vas deferens is blocked, and tubectomy, in which the oviducts are blocked). (b) Prenatal sex determination was being misused for female foeticide, the abortion of female foetuses, because of which the child sex ratio has been declining at an alarming rate in some sections of society; the law was made to stop this misuse. Its benefit in the long run is that a balanced female-male sex ratio is maintained, which a healthy society needs. (c) Bacterial infections: gonorrhoea and syphilis. Viral infections: warts and HIV-AIDS.

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Q312 CBSE 2020
(a) Draw a diagram showing germination of pollen on stigma of a flower and mark on it the following organs/parts :
1. (i)Pollen Grain
2. (ii)Pollen tube
3. (iii)Stigma
4. (iv)Female germ cell (b) State the significance of pollen tube. (c) Name the parts of flower that develop after fertilization into (i) Seed (ii) Fruit
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The pollen tube takes the male germ cell to the female germ cell; the ovule becomes the seed and the ovary the fruit.
(a) The diagram shows the pistil: pollen grains on the sticky stigma, a pollen tube growing from one pollen grain down through the style into the ovary, and an ovule in the ovary with the female germ cell inside it, which the tip of the pollen tube reaches. The four parts asked for are marked on it: pollen grain, pollen tube, stigma and female germ cell. (b) The pollen tube carries the male germ cell from the pollen grain on the stigma, through the style, to the ovule in the ovary, so that it can fuse with the female germ cell; without it, fertilisation cannot take place. (c) (i) The ovule develops into the seed. (ii) The ovary develops into the fruit.

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Q313 CBSE 2020
1. (a)Suggest any two categories of contraceptive methods to control the size of human population which is essential for the prosperity of a country. Also explain about each method briefly.
2. (b)Name two bacterial and two viral infections each that can get sexually transmitted.
3. (c)List two advantages of using condom during sexual act.
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Two contraceptive categories are mechanical barriers (condoms) and hormonal pills; gonorrhoea, syphilis, warts and HIV-AIDS are sexually transmitted; condoms prevent pregnancy and infection.
(a) Any two of these four categories, each with its explanation, earn full credit. Mechanical barrier: a condom on the penis, or a similar covering worn in the vagina, stops the sperms from reaching the egg. Hormonal pills: oral contraceptive pills change the hormonal balance of the body so that eggs are not released. Contraceptive devices: a loop or copper-T placed in the uterus prevents pregnancy. Surgical methods: the vas deferens (vasectomy) or the fallopian tubes (tubectomy) are blocked or cut, so that sperms are not transferred or the egg cannot reach the uterus, and fertilisation does not take place. (b) Bacterial infections: gonorrhoea and syphilis. Viral infections: warts and HIV-AIDS. (c) A condom prevents unwanted pregnancy, because it stops the sperms from reaching the egg; and it helps prevent the transmission of sexually transmitted infections, such as HIV-AIDS, gonorrhoea and syphilis, between the partners.

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Q314 CBSE 2020
Draw a neat diagram showing fertilisation in a flower and label
1. (a)Pollen tube,
2. (b)Male germ cell and
3. (c)Female germ cell, on it. Explain the process of fertilisation in a flower. What happens to the (i) ovary and (ii) ovule after fertilisation ?
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The male germ cell reaches the female germ cell through the pollen tube; the ovary then becomes the fruit and the ovule the seed.
Diagram: the pistil in section, with a pollen grain on the stigma whose pollen tube (a) grows down the style into the ovule in the ovary, carrying the male germ cell (b) to the female germ cell (c) inside the ovule, as in the labelled figure. Process of fertilisation: the pollen grain that lands on the stigma forms a pollen tube, which grows through the style and reaches the ovule; the male germ cell released from it fuses with the female germ cell to form a zygote, which divides to form the embryo. (i) The ovary grows and ripens into the fruit. (ii) The ovule develops a tough coat and becomes the seed.

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Q315 CBSE 2020
1. (a)List the sequence of events in the uterus of a human female from fertilisation of egg till childbirth.
2. (b)State the changes that are observed in the uterus if fertilisation of egg does not occur.
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After fertilisation the embryo implants, is nourished by the placenta and is born after about nine months; otherwise the lining is shed as menstruation.
(a) 1. Fertilisation takes place in the oviduct; the zygote formed divides and reaches the uterus as an embryo. 2. The uterus has prepared itself with a thick lining, richly supplied with blood to nourish the growing embryo, and the embryo gets implanted in it. 3. The embryo gets nutrition from the mother's blood with the help of a special tissue, the placenta: a disc embedded in the uterine wall, with villi on the embryo's side and blood spaces on the mother's side surrounding the villi. 4. Through the placenta, glucose and oxygen pass from the mother's blood to the embryo, and waste substances pass from the embryo to the mother's blood. 5. The child develops inside the mother's body for about nine months. 6. The child is born as a result of rhythmic contractions of the muscles of the uterus. (b) The thick and spongy lining of the uterus is not needed, so it breaks down and comes out through the vagina as blood and mucus. This is menstruation; it lasts about two to eight days and occurs about once a month.

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Q316 CBSE 2020
Based on the given diagram answer the questions given below :
1. (a)Label the parts A, B, C and D.
2. (b)Name the hormone secreted by testis and mention its role.
3. (c)State the functions of B and C in the process of reproduction.
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A is the ureter, B the seminal vesicle, C the urethra, D the vas deferens; the testis secretes testosterone, which regulates sperm formation.
(a) A is the ureter, B the seminal vesicle, C the urethra and D the vas deferens (sperm duct). (b) The testis secretes the hormone testosterone. Its role: it regulates the formation of sperms, and it brings about the changes in appearance seen in boys at the time of puberty. (c) B, the seminal vesicle, adds its secretion to the sperms, so that they are in a fluid that provides them nutrition and makes their transport easier. C, the urethra, is the common passage for both sperms and urine; it carries the sperms out of the body.

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Q317 CBSE 2020
(a) In the female reproductive system of human beings, state the funtions of
1. (i)ovary
2. (ii)oviduct (b) Mention the changes which the uterus undergoes, when (i) it has to receive a zygote. (ii) no fertilization takes place. (c) State the function of placenta.
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The ovary makes eggs, fertilisation occurs in the oviduct, the uterine lining thickens or is shed, and the placenta feeds the embryo.
(a) (i) Ovary: it produces the female germ cells, the eggs (one egg is released every month), and it secretes female hormones such as oestrogen. (ii) Oviduct (fallopian tube): it is the site of fertilisation, where the sperm meets the egg, and it carries the egg from the ovary towards the uterus. (b) (i) The inner lining of the uterus becomes thick and spongy, with a rich blood supply, so that the zygote can be implanted in it and the embryo nourished. (ii) The thickened lining is not needed, so it breaks down and comes out through the vagina as blood and mucus; this is menstruation. (c) The placenta supplies nutrition (glucose) and oxygen from the mother's blood to the developing embryo, and it passes the wastes produced by the embryo into the mother's blood for removal.

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Q318 CBSE 2020
1. (a)“Use of a condom is beneficial for both the sexes involved in a sexual act.” Justify this statement giving two reasons.
2. (b)How do oral contraceptive help in avoiding pregnancies ?
3. (c)What is sex selective abortion ? How does it affect a healthy society ? (State any one consequence)
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A condom prevents pregnancy and infection for both partners; pills stop egg release; sex selective abortion of female foetuses lowers the sex ratio.
(a) A condom is a barrier, and it benefits both partners in two ways. First, it stops the sperms from reaching the egg, so fertilisation cannot take place and an unwanted pregnancy is avoided. Second, it helps to prevent the transmission of sexually transmitted infections such as gonorrhoea, syphilis and HIV-AIDS from one partner to the other, in either direction, so the man and the woman are both protected. (b) Oral contraceptive pills change the hormonal balance of the body so that eggs are not released from the ovaries; with no egg, fertilisation, and so pregnancy, cannot occur. (c) Sex selective abortion is the illegal abortion of a foetus because of its sex, found out by prenatal sex determination; it is done mostly to female foetuses (female foeticide). Consequence: it lowers the female-male sex ratio, which must be maintained for a healthy society.

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Q319 CBSE 2020
1. (a)Draw a diagram to show spore formation in Rhizopus.
2. (b)With the help of an example differentiate between the process of Budding and Fragmentation.
3. (c)Why is vegetative propagation practiced for growing some type of plants ?
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Rhizopus spores form in sporangia; budding keeps the parent whole, fragmentation breaks the organism into pieces; vegetative propagation suits seedless plants.
(a) Diagram: Rhizopus growing on moist bread, with thread-like hyphae spreading over the surface, rhizoids growing down into the bread, and upright hyphae (sporangiophores), each ending in a round sporangium full of spores; one sporangium is shown bursting and releasing its spores. Labels: sporangium, spores, sporangiophore (upright hypha), stolon (spreading hypha) and rhizoids. (b) Budding: a bud forms as an outgrowth at one specific site on the parent, grows into a tiny individual and detaches from the parent, which remains whole; for example, Hydra (or yeast). Fragmentation: a mature organism simply breaks up into two or more pieces (fragments), each of which grows into a new individual; for example, Spirogyra. (c) Vegetative propagation is used to grow plants that do not produce seeds, having lost the capacity to do so, such as banana, orange, rose and jasmine. It also gives plants that bear flowers and fruits earlier than plants raised from seeds, and all of them are genetically similar to the parent plant, so its desirable characteristics are kept.

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Q320 CBSE 2020
(a) What is puberty ? (b) Describe in brief the functions of the following parts in the human male reproductive system :
1. (i)Testes
2. (ii)Seminal vesicle
3. (iii)Vas deferens
4. (iv)Urethra (c) Why are testes located outside the abdominal cavity ? (d) State how sperms move towards the female germ cell.
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Puberty is when reproductive tissues mature; the testes lie outside the abdomen for a cooler temperature, and sperms swim using their tails.
(a) Puberty is the period during adolescence when the reproductive tissues begin to mature, that is, the age at which the reproductive organs of boys and girls become functional. (b) (i) Testes: produce the sperms and secrete the male sex hormone testosterone. (ii) Seminal vesicle: secretes a fluid in which the sperms are carried; this fluid makes their transport easier and provides them with nutrition. (iii) Vas deferens: carries the sperms from the testes; the duct of the seminal vesicle joins it, and it delivers the sperms into the urethra. (iv) Urethra: forms a common passage for both the sperms and the urine, and carries the sperms out of the body. (c) Sperm formation requires a temperature lower than the normal body temperature, so the testes lie outside the abdominal cavity, in the scrotum, which is about $2$ to $2. 5^{\circ}$ C cooler. (d) Each sperm has a long tail, and by moving it the sperm swims through the fluid towards the female germ cell.

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