NCERT Exemplar Solutions Class 10 Science How do Organisms Reproduce

Multiple Choice Questions...........................

Question 1:  In the list of organisms given below, those that reproduce by the asexual method are

(i) banana

(ii) dog

(iii) yeast

(iv) Amoeba

(a) (ii) and (iv)

(b) (i), (iii) and (iv)

(c) (i) and (iv)

(d) (ii), (iii) and (iv) 

Solution 1:  (b) (i), (iii) and (iv)

The dog reproduces sexually, yeast reproduces by budding, Amoeba reproduces sexually, and the cultivated banana reproduces asexually as well.

Question 2:  In a flower, the parts that produce male and female gametes (germ cells) are

(a) stamen and anther

(b) filament and stigma

(c) anther and ovary

(d) stamen and style 

Solution 2:  (c) anther and ovary

Anther and ovary are the male and female parts, in a flower who produces male and female gametes.

Question 3:  Which of the following is the correct sequence of events of sexual reproduction in a flower?

(a) pollination, fertilisation, seedling, embryo

(b) seedling, embryo, fertilisation, pollination

(c) pollination, fertilisation, embryo, seedling

(d) embryo, seedling, pollination, fertilization 

Solution 3:  (c) pollination, fertilisation, embryo, seedling 

Pollination leads to fertilisation, which results in the formation of an embryo. Seedling emerges from the embryo.

Question 4:  Offspring formed by asexual method of reproduction have greater similarity among themselves because

(i) asexual reproduction involves only one parent

(ii) asexual reproduction does not involve gametes

(iii) asexual reproduction occurs before sexual reproduction

(iv) asexual reproduction occurs after sexual reproduction

(a) (i) and (ii)

(b) (i) and (iii)

(c) (ii) and (iv)

(d) (iii) and (iv) 

Solution 4: (a) (i) and (ii) 

Since there is no exchange of gametes during asexual reproduction, the offspring appear identical to their parents.

Question 5:  Characters transmitted from parents to offspring are present in

(a) cytoplasm

(b) ribosome

(c) Golgi bodies

(d) genes 

Solution 5:  (d) genes 

Genes include characteristics passed on from parents to offspring.

Question 6:  Characters that are transmitted from parents to offspring during reproduction show

(a) only similarities with parents

(b) only variations with parents

(c) both similarities and variations with parents

(d) neither similarities nor variations 

Solution 6: (c) both similarities and variations with parents

Characters passed down from parents to offspring during reproduction have both similarities and differences from their parents.

Question 7:  A feature of reproduction that is common to Amoeba, Spirogyra and Yeast is that

(a) they reproduce asexually

(b) they are all unicellular

(c) they reproduce only sexually

(d) they are all multicellular 

Solution 7:  (a) they reproduce asexually

Amoebae replicate via binary fission, Spirogyrae via fragmentation, and yeast via budding.

Question 8:  In Spirogyra, asexual reproduction takes place by

(a) breaking up of filaments into smaller bits

(b) division of a cell into two cells

(c) division of a cell into many cells

(d) formation of young cells from older cells. 

Solution 8:  (a) breaking up of filaments into smaller bits 

Spirogyra propagate by dividing themselves into smaller parts. Spirogyra simply disintegrates into smaller fragments as it ages. These bits or fragments develop into new people.

Question 9:  The ability of a cell to divide into several cells during reproduction in Plasmodium is called

(a) budding

(b) reduction division

(c) binary fission

(d) multiple fission 

Solution 9:  (d) multiple fission

By binary multiple fission, Plasmodium divides into several daughter cells. The cell's nucleus divides several times during mitosis and then splits to form several daughter cells in multiple fission.

Question 10:  The correct sequence of reproductive stages seen in flowering plants is

(a) gametes, zygote, embryo, seedling

(b) zygote, gametes, embryo, seedling

(c) seedling, embryo, zygote, gametes

(d) gametes, embryo, zygote, seedling 

Solution 10:  (a) gametes, zygote, embryo, seedling

During fertilisation, gametes combine to form a zygote. After fertilisation, an embryo is produced, which then develops into a seedling in the plant.

Question 11:  The number of chromosomes in parents and offsprings of a particular species remains constant due to

(a) doubling of chromosomes after zygote formation

(b) halving of chromosomes during gamete formation

(c) doubling of chromosomes after gamete formation

(d) halving of chromosomes after gamete formation 

Solution 11:  (b) halving of chromosomes during gamete formation 

Despite the halving of chromosomes during gamete formation, the number of chromosomes in an organism's somatic cell remains the same. The diploid number of chromosomes refers to the halving of gametes in a cell.

Question 12:  In Rhizopus, tubular thread-like structures bearing sporangia at their tips are called

(a) filaments

(b) hyphae

(c) rhizoids

(d) roots 

Solution 12: (b) hyphae 

Hyphae are tiny blob-on-a-stick-like structures involved in reproduction. The blobs are called sporangia, and they contain cells, or spores, that can grow into new Rhizopus individuals in the future.

Question 13:  Vegetative propagation refers to the formation of new plants from

(a) stem, roots and flowers

(b) stem, roots and leaves

(c) stem, flowers and fruits

(d) stem, leaves and flowers 

Solution 13:  (b) stem, roots and leaves 

Plants use vegetative propagation, which is a form of asexual reproduction. Plants' vegetative components, such as roots, stems, leaves, and buds, are used in vegetative reproduction to grow new plants. Plants developed through vegetative reproduction are genetically similar enough to the parent plant to retain all of its characteristics.

Question 14:  Factors responsible for the rapid spread of bread mould on slices of bread are

(i) large number of spores

(ii) availability of moisture and nutrients in bread

(iii) presence of tubular branched hyphae

(iv) formation of round shaped sporangia

(a) (i) and (iii)

(b) (ii) and iv)

(c) (i) and (ii)

(d) (iii) and (iv) 

Solution 14:  (c) (i) and (ii)

A sufficient number of spores ensures that even in unfavourable circumstances, a few spores survive. The bread's moisture and nutrients provide the perfect atmosphere for the spore to develop into mould.

Question 15:  Length of pollen tube depends on the distance between

(a) pollen grain and the upper surface of the stigma

(b) pollen grain on the upper surface of stigma and ovule

(c) pollen grain in anther and upper surface of stigma

(d) upper surface of stigma and lower part of style 

Solution 15:  (d) upper surface of stigma and lower part of style 

The length of the pollen tube ensures that pollen reaches the stigma, allowing pollination to take place.

Question 16:  Which of the following statements are true for flowers?

(i) Flowers are always bisexual

(ii) They are the sexual reproductive organs

(iii) They are produced in all groups of plants

(iv) After fertilisation, they give rise to fruits

(a) (i) and (iv)

(b) (ii) and (iii)

(c) (i) and (iii)

(d) (ii) and (iv) 

Solution 16:  (d) (ii) and (iv) 

Since flowers are not always bisexual, statement I is incorrect. Since only angiosperms grow flowers, statement iii) is incorrect.

Question 17:  Which among the following statements are true for unisexual flowers?

(i) They possess both stamen and pistil

(ii) They possess either stamen or pistil

(iii) They exhibit cross-pollination

(iv) Unisexual flowers possessing only stamens cannot produce fruits

(a) (i) and (iv)

(b) (ii), (iii) and (iv)

(c) (iii) and (iv)

(d) (i), (iii) and (iv) 

Solution 17: (b) (ii), (iii) and (iv) 

Unisexual flowers, which have either stamen or pistil, need cross-pollination. Fruit cannot be produced by flowers with only stamens because fruit is a mature ovary.

Question 18:  Which among the following statements are true for sexual reproduction in flowering plants?

(i) It requires two types of gametes

(ii) Fertilisation is a compulsory event

(iii) It always results in the formation of zygote

(iv) Offspring formed are clones

(a) (i) and (iv)

(b) (i), (ii) and (iv)

(c) (i), (ii) and (iii)

(d) (i), (ii) and (iv) 

Solution 18:  (c) (i), (ii) and (iii)

Statement iv) is incorrect since offspring created by sexual reproduction cannot be clones.

Question 19:  In the given figure, the parts A, B and C are sequentially

(a) cotyledon, plumule and radicle

(b) plumule, radicle and cotyledon

(c) plumule, cotyledon and radicle

(d) radicle, cotyledon and plumule 

Solution 19: (c) plumule, cotyledon and radical 

Question 20:  Offspring formed as a result of sexual reproduction exhibit more variations because

(a) sexual reproduction is a lengthy process

(b) genetic material comes from two parents of the same species

(c) genetic material comes from two parents of different species

(d) genetic material comes from many parents 

Solution 20:  (b) genetic material comes from two parents of the same species

In sexual reproduction zygote is produced by gametes creates by a male and a female. A male and a female gamete fuse to form a zygote which fertilises to produce new offspring. Offspring have more differences due to the contributions of both parents.

Question 21:  Reproduction is essential for living organisms in order to

(a) keep the individual organism alive

(b) fulfil their energy requirement

(c) maintain growth

(d) continue the species generation after generation 

Solution 21:  d) continue the species generation after generation

Other life processes are required to keep the organism alive, while reproduction is required to maintain the species' lineage.

Question 22:  During adolescence, several changes occur in the human body. Mark one change associated with sexual maturation in boys

(a) loss of milk teeth

(b) increase in height

(c) cracking of voice

(d) weight gain 

Solution 22:  (c) cracking of voice 

Adolescence is a period of transition from childhood to adulthood. Boys go through the following changes:

• Hair growth in new areas of the body, such as armpits, stomach, and between thighs around the genital organ face, legs, and arms.

• Skin becomes oily and pimples appear.

• Penis sometimes erects, particularly when dreaming.

Question 23:  In human females, an event that reflects the onset of the reproductive phase is

(a) growth of body

(b) changes in hair pattern

(c) change in voice

(d) menstruation 

Solution 23: (d) menstruation

Adolescence is a period of transition from childhood to adulthood, Girls go through the following changes:

• Hair growth in new areas of the body, such as armpits and between the thighs near the genital organ; thin hairs on the face, legs, and arms.

• Girls will start menstruating.

• Skin of girls will get oily and pimples will appear.

• Breast size of girls will grow.

Question 24:  In human males, the testes lie in the scrotum, because it helps in the

(a) process of mating

(b) formation of sperm

(c) easy transfer of gametes

(d) all the above 

Solution 24:  (b) formation of sperm 

The temperature of the testes remains lower than the body temperature when they are lying in the scrotum. This aids in the processing of sperm.

Question 25:  Which among the following is not the function of testes at puberty?

(i) formation of germ cells

(ii) secretion of testosterone

(iii) development of placenta

(iv) secretion of estrogen

(a) (i) and (ii)

(b) (ii) and (iii)

(c) (iii)and(iv)

(d) (i) and (iv) 

Solution 25:  (c) (iii) and (iv)

Although the testis is a male reproductive organ, oestrogen is made by females. During pregnancy, a woman's placenta develops.

Question 26:  The correct sequence of organs in the male reproductive system for transport of sperms is

(a) testis → vasdeferens → urethra

(b) testis → ureter → urethra

(c) testis → urethra → ureter

(d) testis → vasdeferens → ureter 

Solution 26:  (a) testis → vasdeferens → urethra 

Sperm are produced in the testis and transferred to the epididymis via vasdeferns. Sperm is brought to the urethra from the vasdeferens.

Question 27:  Which among the following diseases is not sexually transmitted?

(a) Syphillis

(b) Hepatitis

(c) HIV – AIDS

(d) Gonorrhoea 

Solution 27:  (b) Hepatitis 

Hepatitis is transmitted by infected food and water.

Short Answer Questions..........................

Question 28:  In a bisexual flower in spite of the young stamens being removed artificially, the flower produces fruit. Provide a suitable explanation for the above situation. 

Solution 28:  When a bisexual flower's stamens are cut, cross-pollination can occurs resulting in fertilisation and fruit development.

Question 29:  Can you consider cell division as a type of reproduction in unicellular organism? Give one reason. 

Solution 29:  Reproduction is the process of creating a new person. Cell division results in the development of new individuals in unicellular organisms. In unicellular species, cell division is thus a form of reproduction.

Question 30:  What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity? 

Solution 30:  Clone is an asexually generated collection of cells or organisms. Since there is no exchange of gametes during asexual reproduction, the offspring appear identical to their parents.

Question 31:  Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes? 

Solution 31: Since chromosomes are halved during gamete formation, the number of chromosomes in an organism's somatic cells remains the same. A diploid number of chromosomes refers to the halving of gametes in a chromosome.

Question 32:  Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this. 

Solution 32:  Yeast needs energy to expand and divide its cells. Water lacks the required energy, while sugar does, so yeast multiplies in a sugar solution.

Question 33:  Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread? 

Solution 33:  Moisture is needed for bread mould spores to germinate and develop. As a result, mould thrives on a moist slice of bread.

Question 34:  Give two reasons for the appearance of variations among the progeny formed by sexual reproduction. 

Solution 34:

• Crossing over occurs at the time of meiosis.

• Two individuals of the same species contribute gametes.

Question 35:  Would a Planaria cut vertically into two halves regenerate into two individuals? Complete the given figure D and E by indicating the regenerated regions. 

Solution 35:  Yes, Planaria can regenerate into two individuals when split vertically in half.

Question 36:  From the internet, gather information about the chromosome numbers of five animals and five plants. Correlate the number with the size of the organism and answer the following questions.

(a) Do larger organisms have more number of chromosomes/cells?

(b) Can organism with fewer chromosomes reproduce more easily than organisms with more number of chromosomes?

(c) More the number of chromosomes/cells greater is the DNA content. Justify. 

Solution 36:

(a)  The number of chromosomes has little to do with the size of the cell.

(b) In comparison to species with more chromosomes, organisms with fewer chromosomes do not need to replicate as quickly.

(c)  DNA makes up chromosomes. As a result, having more chromosomes requires having more DNA.

Question 37:  In the tobacco plant, the male gametes have twenty-four chromosomes. What is the number of chromosomes in the female gamete? What is the number of chromosomes in the zygote? 

Solution 37:   Since the number of chromosomes in both gametes is the same, the number of chromosomes in a female tobacco plant gamete is 24. In a zygote, the total number of chromosomes is 48.

Question 38:  Why cannot fertilisation take place in flowers if pollination does not occur? 

Solution 38:   Pollination is the process of pollen grains being transferred from anthers to stigma. There will be no fusion of gametes if pollination does not occur, and fertilisation will not occur.

Question 39:  Is the chromosome number of the zygote, embryonal cells and adult of a particular organism always constant? How is the constancy maintained in these three stages? 

Solution 39:   Meiosis is a cell division process that involves halving a number of chromosomes. Chromosomes become equal to those of somatic cells after fertilisation. Mitosis occurs for the remainder of a person's life after fertilisation. As a result, chromosomes do not alter.

Question 40:  Where is the zygote located in the flower after fertilization? 

Solution 40:   The zygote will be found in the ovary after fertilisation.

Question 41:  Reproduction is linked to stability of population of a species. Justify the statement. 

Solution 41:   Predation and competition for food are natural in nature. Species would have gone extinct if there was no breeding. As a result, reproduction is related to the species' population.

Question 42:  How are general growth and sexual maturation different from each other? 

Solution 42:   The term "general growth" refers to the expansion of one's physical size. The ability to reproduce is the aim of sexual maturation. Sexual maturity is reached at a stage of life called puberty, while general development starts with the growth of an organism.

Question 43:  Trace the path of sperm during ejaculation and mention the gland and their functions associated with the male reproductive system. 

Solution 43:   The path of sperm in the male reproductive system during ejaculation is testis → epididymis → vasdeferens → prostate→ urethra.

Question 44:  What changes are observed in the uterus if fertilisation does not occur? 

Solution 44:   If fertilisation does not occur, the following modifications occur in the uterus:

• Extra uterine lining degenerates.

• Uterus lining fragments are discharged through the vaginal canal.

• Unfertilized egg is discharged.

• Menstruation occurs.

Question 45:  What changes are observed in the uterus subsequent to implantation of the young embryo? 

Solution 45:   Following the implantation of the young embryo, the uterus undergoes the following modifications.

• The uterine lining thickens in order to protect the growing embryo. (PLACENTA)

• The uterine lining is densely packed with blood vessels, allowing nutrients and oxygen to reach the developing foetus.

Question 46:  What are the benefits of using mechanical barriers during sexual act? 

Solution 46:

• Mechanical barriers reduce the chances of unintended pregnancies.

• Mechanical barriers to deter sexually transmitted diseases.

Question 47:  In the given figure, label the parts and mention their functions.

(a) Production of egg

(b) Site of fertilisation

(c) Site of implantation

(d) Entry of the sperms

Solution 47:

(a) Ovary

(b) Oviduct

(c) Uterus

(d) Vaginal passage

Question 48:  What would be the ratio of chromosome number between an egg and its zygote? How is the sperm genetically different from the egg? 

Solution 48:   An egg and its zygote have a chromosome number ratio of 1:2.

The father's genetic material is found in sperm, while the mother's genetic material is found in eggs. The X or Y chromosome can be found in sperm, but the X chromosome is still present in eggs.

Long Answer Questions..........................

Question 49:  Why budding, fragmentation and regeneration all are considered as asexual types of reproduction? With neat diagrams explain the process of regeneration in Planaria. 

Solution 49:   Since only one parent is involved in budding, fragmentation, and regeneration, and no gametes are created, these forms of reproduction are classified as asexual. 

Diagrammatically representation of the process of regeneration of Planaria:

A planaria's body is divided into components, each of which has the potential to develop into a new organism. In the diagram above, the planaria body is divided into three components, each of which regenerates into three individual cells.

Question 50:  Write two points of difference between asexual and sexual types of reproduction. Describe why variations are observed in the offspring formed by sexual reproduction. 

Solution 50:

When compared to asexual reproduction, there are more differences in sexual reproduction. The explanations for this are as follows.

• Crossing over that occurs during meiosis results in further variance.

• Two parents contribute to the gene pool.

• Variation is also influenced by DNA replication.

Question 51:  Distinguish between pollination and fertilisation. Mention the site and product of fertilisation in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule. 

Solution 51:

Question 52:  Distinguish between a gamete and zygote. Explain their roles in sexual reproduction. 

Solution 52:

Question 53:  Draw the diagram of a flower and label the four whorls. Write the names of gamete producing organs in the flower. 

Solution 53:   Female gametes are produced by the ovary. Male gametes are generated by anthers.

Question 54:  What is placenta? Mention its role during pregnancy?   

Solution 54:  The placenta is a disc that is implanted in the uterine wall during pregnancy. In the embryo's side of the tissue, there are villi. The villi are surrounded by blood spaces on the mother's hand. This allows glucose and oxygen to transfer from the mother to the embryo over a wide surface area. With the assistance of the placenta, the embryo receives nutrients from the mother's blood. Waste products are produced by the developing embryo and can be extracted by moving them into the mother's bloodstream through the placenta.

Question 55:  What are various ways to avoid pregnancy? Elaborate any one method. 

Solution 55:  Listed below are some methods for avoiding pregnancy:

(a) Physical impediment

(b) Hormone Pills

(c) Copper-T

(d) Surgical technique

Method of constructing a barrier:

Physical instruments such as diaphragms (or caps) and condoms are used in barrier methods of avoiding pregnancy. Human females wear a diaphragm (or cap) that covers their cervix. Males are the ones that use condoms.

Question 56:  How does fertilisation take place? Fertilisation occurs once in a month. Comment. 

Solution 56:   One egg is released from each of the ovaries once a month. The egg is passed from the ovaries to the fallopian tube. Just one sperm will enter the egg at a time as sperm migrate into the fallopian tube. Fertilization is the term for this operation.

A menstrual cycle lasts about 28 days. This means that in each menstrual cycle, only one egg is required for fertilisation. As a result, fertilisation can only take place once per month.

Question 57:  Reproduction is essentially a phenomenon that is not for the survival of an individual but for the stability of a species. Justify. 

Solution 57:   Predation and competition for food are natural in nature. Species would have gone extinct if there was no breeding. As a result, reproduction is related to a species' population. The lineage of new individuals is passed down from their ancestors. The increased number of species counterbalances the mortality that occurs as a result of different factors. Reproduction, for example, aids in the maintenance of a species' equilibrium.

Question 58:  Describe sexually transmitted diseases and mention the ways to prevent them. 

Solution 58:   Sexually transmitted diseases are diseases that spread from one person to another through sexual contact. Bacterial infections like gonorrhoea and syphilis, as well as viral infections like warts and HIV-AIDS, are among them.

The methods for preventing sexually transmitted diseases are listed below.

• Have a hepatitis B vaccine.
• Do not share towels or underwear.
• By using condoms or other physical barriers.
• Avoiding sexual contact with unknown partners.