CBSE Class 10 Science How do humans reproduce Sure Shot Questions Set 03

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ASSIGNMENT QUESTIONS SET - 3
CHAPTER - 8
HOW DO ORGANISMS REPRODUCE?

1. In the list of organisms given below, those that reproduce by the asexual method are
(i) banana
(ii) dog
(iii) yeast
(iv) Amoeba

Answer:
1. Banana reproduces vegetatively, which is a form of asexual reproduction.
2. Yeast reproduces asexually by budding.
3. Amoeba reproduces asexually by binary fission.
4. Dog reproduces sexually, so option (ii) is excluded.
5. Hence, the asexual organisms are (i) banana, (iii) yeast and (iv) Amoeba.

Teacher's Note:
a) Asexual reproduction needs only one parent and no gametes.
b) Budding, binary fission and vegetative propagation are all asexual methods.
c) Animals such as dogs reproduce only sexually.

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

Answer: (c) anther and ovary

1. The anther, part of the stamen, produces pollen grains which carry the male gametes.
2. The ovary, part of the pistil, contains ovules which carry the female gametes.
3. Hence, the correct option is (c).

Teacher's Note:
a) Stamen is the male reproductive part, but only the anther makes pollen.
b) Filament only holds the anther, and stigma only receives pollen.

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, fertilisation

Answer: (c) pollination, fertilisation, embryo, seedling

1. Pollination places pollen on the stigma.
2. Fertilisation follows when the male and female gametes fuse.
3. The zygote develops into an embryo, which grows into a seedling.
4. Hence, the correct order is pollination, fertilisation, embryo, seedling.

Teacher's Note:
a) An embryo forms before a seedling can grow.
b) Pollination always comes first in the sequence.
c) Watch the order of embryo and seedling, a common mistake in options.

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)

Answer: (a) (i) and (ii)

1. Asexual reproduction involves only one parent, so there is no mixing of genes from two parents.
2. No gametes are involved, so there is no fusion of different genetic material.
3. Statements (iii) and (iv) describe timing, which does not explain similarity.
4. Hence, the correct option is (a).

Teacher's Note:
a) Offspring from one parent are copies of that parent, so they look alike.
b) The timing of asexual and sexual reproduction in a life cycle does not cause similarity.

5. Characters transmitted from parents to offspring are present in
(a) cytoplasm
(b) ribosome
(c) golgi bodies
(d) genes

Answer: (d) genes

1. Characters are inherited through hereditary units.
2. These hereditary units are called genes, which are present on chromosomes.
3. Hence, the correct option is (d).

Teacher's Note:
a) Genes are the units of inheritance and are made of DNA.
b) Cytoplasm, ribosomes and Golgi bodies do not carry hereditary information.

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

Answer: (c) both similarities and variations with parents

1. Offspring inherit characters from both parents, so they resemble their parents.
2. Because genetic material is mixed in sexual reproduction, offspring also show some differences.
3. Hence, the correct option is (c).

Teacher's Note:
a) Similarity comes from inheritance of the parents' genes.
b) Variation comes from new combinations of genes, which is why siblings differ.

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

Answer: (a) they reproduce asexually

1. Amoeba reproduces by binary fission, Spirogyra by fragmentation and Yeast by budding.
2. All three reproduce asexually.
3. Spirogyra is a filamentous organism made of many cells, so option (b) is wrong.
4. Hence, the correct option is (a).

Teacher's Note:
a) Spirogyra is multicellular, so it is not unicellular like Amoeba and yeast.
b) Shared features among organisms should be checked against each example.

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.

Answer: (a) breaking up of filaments into smaller bits

1. Spirogyra grows as long unbranched filaments.
2. Each filament breaks into smaller pieces, and each piece grows into a new filament.
3. This process is called fragmentation, so the correct option is (a).

Teacher's Note:
a) Fragmentation is the breaking of a filament into pieces that grow into new individuals.
b) Option (b) describes binary fission, which is not how Spirogyra reproduces.

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

Answer: (d) multiple fission

1. In Plasmodium, one cell divides into many daughter cells at the same time.
2. This type of division is called multiple fission.
3. Hence, the correct option is (d).

Teacher's Note:
a) Binary fission divides a cell into only two cells.
b) Reduction division is meiosis, which halves the chromosome number.

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

Answer: (a) gametes, zygote, embryo, seedling

1. Male and female gametes are produced first.
2. Their fusion forms the zygote.
3. The zygote develops into an embryo, which grows into a seedling.
4. Hence, the correct option is (a).

Teacher's Note:
a) Gametes must be formed before a zygote can be made.
b) An embryo is the stage that develops from the zygote inside the seed.

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

Answer: (b) halving of chromosomes during gamete formation

1. Gametes are formed by meiosis, in which the chromosome number is halved.
2. At fertilisation, two gametes fuse and the full chromosome number is restored in the zygote.
3. Halving during gamete formation keeps the number constant from parents to offspring.
4. Hence, the correct option is (b).

Teacher's Note:
a) Meiosis halves the chromosome number, and fertilisation restores it.
b) Doubling happens at fertilisation, not after the gametes are formed.
c) Keep the parents' and offspring's chromosome numbers the same in every generation.

12. In Rhizopus, tubular thread-like structures bearing sporangia at their tips are called
(a) filaments
(b) hyphae
(c) rhizoids
(d) roots

Answer: (b) hyphae

1. The body of Rhizopus is made of long, branched, tubular threads.
2. These threads are called hyphae.
3. Hence, the correct option is (b).

Teacher's Note:
a) A group of hyphae forms the mycelium of the fungus.
b) Rhizoids are root-like anchoring structures, not reproductive threads.

13. Vegetative propagation refers to 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

Answer: (b) stem, roots and leaves

1. Vegetative propagation uses vegetative parts of the plant.
2. Stem, roots and leaves are vegetative parts that can form new plants.
3. Flowers and fruits are reproductive parts, so options (a), (c) and (d) are wrong.
4. Hence, the correct option is (b).

Teacher's Note:
a) Potato eyes, runners and leaf buds are examples of vegetative propagation.
b) Flowers and fruits are not vegetative parts.

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)

Answer: (c) (i) and (ii)

1. Bread mould produces a large number of spores, which are carried by air and spread to new places.
2. Bread provides moisture and nutrients, which help spores germinate and grow.
3. Hyphae and sporangia are part of the body structure, not the cause of rapid spread.
4. Hence, the correct option is (c).

Teacher's Note:
a) Spores are light and are dispersed easily by air.
b) Moisture and nutrients are the two main needs for growth of a mould.

15. Length of pollen tube depends on the distance between
(a) pollen grain and upper surface of stigma
(b) pollen grain on 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

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

1. After landing on the stigma, the pollen grain grows a pollen tube.
2. The pollen tube grows down the style to reach the ovule.
3. So the length of the pollen tube depends on the distance between the pollen grain on the stigma and the ovule.
4. Hence, the correct option is (b).

Teacher's Note:
a) The pollen tube carries male gametes down the style.
b) The longer the style, the longer the pollen tube must grow.

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)

Answer: (d) (ii) and (iv)

1. Flowers are not always bisexual, because unisexual flowers also exist, so (i) is false.
2. Flowers are the sexual reproductive organs of angiosperms, so (ii) is true.
3. Flowers are not found in all plant groups, since algae, mosses and ferns have none, so (iii) is false.
4. After fertilisation, the ovary develops into a fruit, so (iv) is true.
5. Hence, the correct option is (d).

Teacher's Note:
a) Unisexual flowers have either stamens or a pistil.
b) Flowers are found only in flowering plants.
c) After fertilisation, the ovary becomes the fruit.

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)

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

1. A unisexual flower has either stamens or a pistil, not both, so (i) is false and (ii) is true.
2. Since one flower cannot provide both gametes, pollen usually comes from another flower, which means cross pollination, so (iii) is true.
3. A flower with only stamens has no ovary, so it cannot produce fruit, and (iv) is true.
4. Hence, the correct option is (b).

Teacher's Note:
a) Unisexual flowers are often found on different plants or on the same plant.
b) Cross pollination is the usual route for unisexual flowers.
c) No ovary means no fruit.

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 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)

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

1. Sexual reproduction needs male and female gametes, so (i) is true.
2. Fertilisation is essential in sexual reproduction, so (ii) is true.
3. Fusion of the gametes forms a zygote, so (iii) is true.
4. Offspring of sexual reproduction are not clones, because they carry a mix of genes from two parents, so (iv) is false.
5. Hence, the correct option is (c).

Teacher's Note:
a) Clones come only from asexual reproduction.
b) Two gametes are needed to form one zygote.
c) Options (b) and (d) both include the false statement (iv), so they cannot be correct.

19. In the below 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

[Figure: Diagram of a dicot seed embryo split lengthwise, showing two large green cotyledons with the embryonic axis in between. Label A points to the upper end of the embryonic axis, the plumule. Label B points to one of the cotyledons. Label C points to the lower end of the embryonic axis, the radicle.]

Answer: (c) plumule, cotyledon and radicle

1. A points to the upper tip of the embryonic axis, which is the plumule.
2. B points to a cotyledon, the seed leaf that stores food.
3. C points to the lower end of the embryonic axis, which is the radicle.
4. Hence, the correct option is (c).

Teacher's Note:
a) The plumule grows into the shoot and the radicle grows into the root.
b) Cotyledons store food for the developing embryo.

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

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

1. Sexual reproduction combines genetic material from two parents.
2. The two parents belong to the same species, so they can produce fertile offspring.
3. Mixing of the two sets of genes gives new combinations, which produce variation.
4. Hence, the correct option is (b).

Teacher's Note:
a) Variation is produced by mixing genes, not by the time taken to reproduce.
b) Parents from different species usually cannot produce fertile offspring.

21. Reproduction is essential for living organisms in order to
(a) keep the individual organism alive
(b) fulfill their energy requirement
(c) maintain growth
(d) continue the species generation after generation

Answer: (d) continue the species generation after generation

1. Individual organisms die after a limited life span.
2. Reproduction produces new individuals that carry the species forward.
3. Hence, the correct option is (d).

Teacher's Note:
a) Reproduction is for the survival of the species, not of the individual.
b) Energy and growth are needed by the individual, not by reproduction itself.

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

Answer: (c) cracking of voice

1. Sexual maturation is driven by hormones from the testes in boys.
2. Cracking of voice happens because the larynx grows under this hormonal action.
3. Loss of milk teeth, increase in height and weight gain are general growth changes, not signs of sexual maturation.
4. Hence, the correct option is (c).

Teacher's Note:
a) Sexual maturation changes are caused by sex hormones.
b) General growth also occurs in both boys and girls, so it is not a sign of maturation.

23. In human females, an event that reflects onset of reproductive phase is
(a) growth of body
(b) changes in hair pattern
(c) change in voice
(d) menstruation

Answer: (d) menstruation

1. Menstruation is the monthly discharge of the uterine lining.
2. Its first occurrence at puberty marks the onset of the reproductive phase in girls.
3. Hence, the correct option is (d).

Teacher's Note:
a) Menarche is the first menstruation.
b) Growth of body and changes in hair pattern happen in both sexes and are not reproductive markers.

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

Answer: (b) formation of sperm

1. Sperm formation needs a temperature slightly lower than the body temperature.
2. The scrotum, outside the abdomen, keeps the testes at this lower temperature.
3. Hence, the correct option is (b).

Teacher's Note:
a) Testes placed inside the body would be too warm for sperm formation.
b) Mating and transfer of gametes are not the reason the testes lie in the scrotum.

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)

Answer: (c) (iii) and (iv)

1. The testes form germ cells (sperm), so (i) is a function.
2. The testes secrete testosterone at puberty, so (ii) is a function.
3. The placenta develops in pregnant females, not in the testes, so (iii) is not a function.
4. Estrogen is secreted by the ovaries in females, so (iv) is not a function of the testes.
5. Hence, the correct option is (c).

Teacher's Note:
a) Testosterone causes the changes of puberty in boys.
b) The placenta is an organ of pregnancy and is not found in males.

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

Answer: (a) testis → vasdeferens → urethra

1. Sperms are produced in the testis.
2. They pass through the vas deferens to the urethra.
3. The urethra carries sperms out of the body.
4. The ureter carries urine from the kidney, not sperms, so options (b), (c) and (d) are wrong.
5. Hence, the correct option is (a).

Teacher's Note:
a) The urethra is shared by the urinary and reproductive systems in males.
b) The ureter is a urinary tube and never carries sperms.

27. Which among the following diseases is not sexually transmitted?
(a) Syphillis
(b) Hepatitis
(c) HIV - AIDS
(d) Gonorrhoea

Answer: (b) Hepatitis

1. Syphilis is a sexually transmitted disease.
2. HIV-AIDS is a sexually transmitted disease.
3. Gonorrhoea is a sexually transmitted disease.
4. Hepatitis is mainly spread through contaminated food, water and body fluids, and it is not listed among the sexually transmitted diseases in this group.
5. Hence, the correct option is (b).

Teacher's Note:
a) Hepatitis A and E spread mainly through contaminated food and water.
b) Hepatitis B can also spread through body fluids, so learn the STD list from your textbook.
c) Syphilis, gonorrhoea and HIV-AIDS are classic examples of sexually transmitted diseases.

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

Answer:
1. Removing the young stamens prevents self-pollination within the same flower.
2. The flower still produces fruit because pollen from another flower of the same species reached its stigma.
3. This pollen germinated, the pollen tube reached the ovule, and fertilisation took place.
4. The ovary therefore developed into a fruit.

Teacher's Note:
a) Removing stamens before they release pollen is called emasculation.
b) Fruit formation depends on fertilisation, not on the presence of stamens in the same flower.
c) Cross pollination by wind or insects can still bring pollen to the stigma.

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

Answer:
1. Yes, cell division can be considered a type of reproduction in unicellular organisms.
2. Reason: in Amoeba and other unicellular organisms, each cell divides to form two or more new cells, and each new cell is a complete individual.

Teacher's Note:
a) In unicellular organisms, division of the single cell increases the number of individuals.
b) This is the same as binary fission in Amoeba.

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

Answer:
1. A clone is a group of genetically identical individuals produced from a single parent by asexual reproduction.
2. Offspring formed by asexual reproduction show remarkable similarity because they come from one parent and no gametes are involved.
3. The genetic material is copied from the parent with little or no change, so the offspring are almost identical to the parent.

Teacher's Note:
a) Clones are copies of the parent, so they are identical in genes.
b) Because there is no mixing of genes, variation is very small.
c) Bacteria and yeast cells produced by division are examples of clones.

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

Answer:
1. Gametes are formed by meiosis, and each gamete has half the number of chromosomes of the parent.
2. During fertilisation, the male and female gametes fuse, so the zygote has the full number of chromosomes.
3. The zygote develops into the offspring, which therefore has the same chromosome number as its parents.

Teacher's Note:
a) Halving at gamete formation and doubling at fertilisation keep the number constant.
b) Without halving, the chromosome number would double in every generation.

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

Answer:
1. Yeast needs food for growth and multiplication.
2. Sugar solution provides the sugar that yeast uses as food, but plain water does not.

Teacher's Note:
a) Yeast feeds on sugar and ferments it to produce carbon dioxide and alcohol.
b) Water alone has no nutrients for the yeast to grow.

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

Answer:
1. Bread mould needs moisture for its spores to germinate and its hyphae to grow.
2. A moist slice provides the water needed for growth, but a dry slice does not.

Teacher's Note:
a) Moisture and nutrients together support rapid mould growth.
b) Keeping bread dry in a closed bin slows down mould growth.

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

Answer:
1. Genetic material comes from two different parents, so the offspring get a mix of genes from both.
2. During gamete formation, chromosomes are shuffled and exchange segments, and random fusion of gametes gives new gene combinations.

Teacher's Note:
a) Mixing of genes from two parents is the main source of variation.
b) Crossing over during meiosis creates new combinations on the same chromosome.

35. Would a Planaria cut vertically into two halves regenerate into two individuals? Complete the below Figure D and E by indicating the regenerated regions.

[Figure: Five drawings of Planaria labelled A to E. A shows a whole planarian. B shows the same planarian with a dotted vertical line down its middle to mark the cut. C shows the two halves of the planarian placed side by side. D shows the left half of the planarian. E shows the right half of the planarian. The regenerated regions are to be drawn on D and E.]

Answer:
1. Yes, a Planaria cut vertically into two halves regenerates into two individuals.
2. Each half regenerates the body part that was lost at the cut surface.
3. In D, the left half regrows the missing right half, forming a complete Planaria.
4. In E, the right half regrows the missing left half, forming a second complete Planaria.

Teacher's Note:
a) Planaria has a high power of regeneration because its body contains many dividing cells.
b) Each half must regrow the missing side to become a complete individual.
c) Regeneration in Planaria is a type of asexual reproduction.

36. From the internet, gather information about the chromosome numbers of five animals and five plants. Correlate the number with the size of 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.

Answer:
1. Chromosome numbers vary widely; for example, humans have 46, onion 16, maize 20, fruit fly 8 and the fern Ophioglossum about 1260.
2. (a) No. Chromosome number does not match body size, since the fruit fly is much smaller than the human but its chromosome number is smaller than the human's too, while the fern has a very large number of chromosomes.
3. (b) No. Ease of reproduction depends on the life cycle and the environment, not on the number of chromosomes.
4. (c) Each chromosome is made of DNA, so more chromosomes generally means more DNA in the nucleus. However, the DNA content per chromosome varies, so the link is only general.

Teacher's Note:
a) Chromosome number is a feature of the species, not a measure of size.
b) Students should cite the source of each chromosome number collected from the internet.
c) Number of cells in an organism is not fixed by its chromosome number.

37. In 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?

Answer:
1. The male gamete has 24 chromosomes, so the gametes of this species have the haploid number, n = 24.
2. The female gamete has the same number, so it has 24 chromosomes.
3. The zygote is formed by fusion of the two gametes, so it has 24 + 24 = 48 chromosomes.

Teacher's Note:
a) Male and female gametes of a species carry the same haploid number.
b) The zygote always has the diploid number, which is twice the gamete number.

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

Answer:
1. Male gametes are carried in pollen grains, which must first reach the stigma.
2. Without pollination, no pollen lands on the stigma, so no pollen tube grows.
3. The male gametes cannot reach the ovule to fuse with the egg, so fertilisation cannot take place.

Teacher's Note:
a) Pollination is the transfer of pollen to the stigma.
b) Pollen tube growth down the style is needed to carry the male gametes to the ovule.

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

Answer:
1. Yes, the chromosome number of the zygote, embryonal cells and adult of a species is constant.
2. The zygote has the full (diploid) number, formed when the gametes fuse.
3. Embryonal cells and adult body cells are produced by mitosis, which copies and shares the chromosomes equally, so the number stays the same.
4. Gametes are formed by meiosis with half the number, and fertilisation restores the full number, so the constancy is maintained across generations.

Teacher's Note:
a) Mitosis gives two cells with the same number of chromosomes as the parent cell.
b) Meiosis and fertilisation together keep the number constant from one generation to the next.

40. Where is the zygote located in the flower after fertilization?

Answer: After fertilisation, the zygote is located inside the ovule, and the ovule is inside the ovary at the base of the pistil.

Teacher's Note:
a) The zygote develops into an embryo inside the ovule.
b) The ovule becomes the seed, and the ovary becomes the fruit.

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

Answer:
1. Individuals die naturally after a certain life span.
2. Reproduction produces new individuals to replace those that have died.
3. When births balance deaths, the number of individuals in the population stays stable, so the species continues.

Teacher's Note:
a) A population that does not reproduce will shrink and may disappear.
b) Stable numbers depend on a balance between births and deaths.

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

Answer:
1. General growth is the increase in height, weight and size of the body, and it occurs in all parts of the body.
2. Sexual maturation is the development of reproductive organs and the ability to produce gametes, and it occurs at puberty under the action of sex hormones.

Teacher's Note:
a) General growth continues for a long time, but sexual maturation happens during puberty.
b) Sex hormones control sexual maturation, while general growth depends on other factors.

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

Answer:
1. Path of sperm: testis → vas deferens → ejaculatory duct → urethra → out through the penis.
2. Seminal vesicles: secrete a fluid rich in fructose that gives energy to the sperms.
3. Prostate gland: secretes a fluid that makes the medium alkaline and helps the sperms to move.
4. Cowper's (bulbourethral) glands: secrete a lubricating fluid that cleans the urethra and eases the passage of sperms.

Teacher's Note:
a) The sperm mixes with the secretions of the glands to form semen.
b) The urethra carries both semen and urine, but never at the same time.

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

Answer:
1. The lining of the uterus, which had thickened to receive the embryo, is not needed.
2. The thick lining breaks down and is shed along with blood through the vagina.
3. This shedding is called menstruation, and the cycle starts again.

Teacher's Note:
a) Menstruation happens about once a month when no pregnancy occurs.
b) The uterine lining is rebuilt in the next cycle.

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

Answer:
1. The uterine lining is maintained and becomes thicker, with more blood vessels.
2. The uterus is prepared to support the growing embryo, which gets nutrition from the mother's blood.
3. Menstruation stops during pregnancy because the lining is not shed.

Teacher's Note:
a) Stopping of menstruation is an early sign of pregnancy.
b) The uterus expands greatly as the embryo grows.

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

Answer:
1. A mechanical barrier, such as a condom, stops sperms from entering the female reproductive tract, so pregnancy is avoided.
2. It also prevents the spread of sexually transmitted diseases, including HIV-AIDS.

Teacher's Note:
a) Condoms are the most common mechanical barrier method.
b) They protect against both pregnancy and infection, so they are a dual-purpose choice.

47. In the given below 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

[Figure: Diagram of the human female reproductive system. Two ovaries are shown on either side at the top, joined to two fallopian tubes that curve towards the central uterus. The uterus is drawn in the centre with its inner lining shaded in red. Below the uterus is the narrow cervix and the vagina. No letters or labels are printed in the figure.]

Answer:
1. (a) Production of egg: the ovary, which produces the ova.
2. (b) Site of fertilisation: the fallopian tube (oviduct), where the sperm fuses with the egg.
3. (c) Site of implantation: the uterus, where the embryo embeds in the lining.
4. (d) Entry of the sperms: the vagina, through which sperms enter the female tract during the sexual act.

Teacher's Note:
a) The ovary produces the egg and the hormones oestrogen and progesterone.
b) Fertilisation happens in the upper part of the fallopian tube, not in the uterus.
c) The uterus is where the embryo develops and grows.

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

Answer:
1. An egg has the haploid number, n, of chromosomes, and its zygote has the diploid number, 2n.
2. So the ratio of chromosome number between the egg and its zygote is n : 2n, which is 1 : 2.
3. In humans, the egg always carries an X chromosome, while the sperm can carry either an X or a Y chromosome.
4. Sperms also differ from one another in their gene combinations, because each is formed by a different shuffle of chromosomes.

Teacher's Note:
a) Haploid means one set of chromosomes, and diploid means two sets.
b) The sex of a human child is decided by the sperm, not by the egg.

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

Answer:
1. Budding, fragmentation and regeneration all need only one parent, and no gametes are formed or fused.
2. Each new individual is produced from the body of a single parent by mitotic division or regrowth.
3. In Planaria, when the body is cut into pieces, each piece has specialised cells that divide and form the missing parts.
4. Each piece therefore grows into a complete new Planaria.
5. [Figure: diagram to be added]

Teacher's Note:
a) Regeneration is the ability to regrow lost body parts.
b) Diagrams should show the cut lines and the regrown head or tail on each piece.
c) Planaria is a flatworm with a strong regenerative power.

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.

Answer:
1. Asexual reproduction involves one parent, while sexual reproduction usually involves two parents.
2. Asexual reproduction does not involve gametes, while sexual reproduction involves the fusion of male and female gametes.
3. Variations appear in sexual reproduction because genetic material from two parents is mixed, and the shuffling of chromosomes during gamete formation creates new combinations of genes.

Teacher's Note:
a) Offspring of asexual reproduction are almost identical to the parent.
b) Offspring of sexual reproduction are different from both parents and from each other.

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

Answer:

Difference between pollination and fertilisation

Site of fertilisation: the ovule, inside the ovary of the flower.
Product of fertilisation: the zygote, which develops into an embryo.

Teacher's Note:
a) Pollination can happen without fertilisation, but fertilisation always follows successful pollination.
b) After fertilisation, the ovule becomes the seed and the ovary becomes the fruit.
c) Insects and wind help in pollination, not in fertilisation.

52. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule.

Answer:
1. The diagram shows the pistil with the stigma at the top, the style below it, and the ovary at the base containing the ovules.
2. A pollen grain lands on the stigma and grows a pollen tube.
3. The pollen tube grows down through the style and enters the ovary.
4. The pollen tube enters the ovule through the micropyle and releases the male gametes.
5. [Figure: diagram to be added]

Teacher's Note:
a) Label the stigma, style, ovary, ovule, pollen grain, pollen tube and micropyle.
b) Draw the pollen tube as a thin tube that grows from the grain to the ovule.

53. Distinguish between a gamete and zygote. Explain their roles in sexual reproduction.

Answer:
1. A gamete is a haploid reproductive cell, such as a sperm or an egg, with half the number of chromosomes.
2. A zygote is a diploid cell formed when two gametes fuse during fertilisation.
3. Gametes carry the genetic material from each parent to the next generation, and their fusion restores the full chromosome number.
4. The zygote divides and develops into an embryo, which grows into a new individual.

Teacher's Note:
a) Gametes are formed by meiosis, while the zygote is the first cell of the new individual.
b) A zygote has two sets of chromosomes, one from each parent.

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

Answer:
1. The diagram shows a flower with four whorls, drawn from the outside in: calyx (sepals), corolla (petals), androecium (stamens) and gynoecium (pistil).
2. The stamen, made of filament and anther, produces pollen grains, which carry the male gametes.
3. The pistil, made of stigma, style and ovary, contains ovules, which carry the female gametes.
4. Hence, the gamete producing organs are the anther (male) and the ovary (female).
5. [Figure: diagram to be added]

Teacher's Note:
a) The calyx and corolla are protective whorls and are not reproductive parts.
b) Androecium is the male part and gynoecium is the female part of the flower.
c) Label the four whorls in the order calyx, corolla, androecium and gynoecium.

55. What is placenta? Mention its role during pregnancy?

Answer:
1. The placenta is a disc-shaped organ formed from embryonic and maternal tissues, embedded in the wall of the uterus.
2. It supplies oxygen and nutrients from the mother's blood to the embryo through the umbilical cord.
3. It removes carbon dioxide and waste products from the embryo.
4. It also produces hormones that help to maintain pregnancy.

Teacher's Note:
a) Mother's blood and the embryo's blood do not mix in the placenta.
b) The placenta is expelled after delivery of the baby.

56. What are various ways to avoid pregnancy? Elaborate any one method.

Answer:
1. Methods to avoid pregnancy include barrier methods (condoms, diaphragm), intrauterine devices (IUD), oral contraceptive pills, surgical methods (vasectomy and tubectomy) and natural methods (safe period).
2. Elaboration of condoms: a condom is a thin sheath made of latex that is put over the erect penis before sexual intercourse.
3. It traps the sperms, so they cannot enter the female reproductive tract, and it also protects against sexually transmitted diseases.

Teacher's Note:
a) Condoms should be put on before any contact between the penis and the vagina.
b) Pills and IUDs prevent pregnancy by hormonal or mechanical action, not by blocking sperms at the entrance.
c) Choose a method after medical advice.

57. What are placenta ? Explain its structure and function.

Answer:
1. Structure: the placenta is a disc-shaped tissue, with finger-like villi from the embryo's side that project into blood spaces of the mother's uterine wall.
2. The embryo is connected to the placenta by the umbilical cord, which carries blood vessels.
3. Function: it allows the transfer of oxygen and nutrients from the mother to the embryo.
4. It removes carbon dioxide and waste from the embryo and produces hormones that support pregnancy.

Teacher's Note:
a) The villi increase the surface area for exchange of substances.
b) Substances pass by diffusion, and the blood of mother and embryo do not directly mix.

58. How does fertilisation take place? Fertilisation occurs once in a month. Comment.

Answer:
1. Fertilisation takes place in the upper part of the fallopian tube, when a sperm enters the ovum and its nucleus fuses with the nucleus of the ovum.
2. The ovum is released once a month during ovulation, so an ovum is available for fertilisation about once a month.
3. Fertilisation does not always occur in that month; it happens only if sperms reach the ovum within about a day of its release.
4. Hence, the statement is only partly correct: an egg is available once a month, but fertilisation depends on sperms being present.

Teacher's Note:
a) The fused cell formed by fertilisation is the zygote.
b) An ovum survives only for a short time, so timing matters.

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

Answer:
1. Every individual organism has a limited life span and dies after some time.
2. Reproduction does not extend the life of the individual, but it produces new individuals to carry on the species.
3. Continuous production of new individuals keeps the population stable over generations, so the species survives.

Teacher's Note:
a) An individual survives by feeding and growing, while a species survives by reproducing.
b) Stable populations depend on regular reproduction.

60. Describe sexually transmitted diseases and mention the ways to prevent them.

Answer:
1. Sexually transmitted diseases (STDs) are infections that spread from one person to another mainly through sexual contact. Examples are gonorrhoea, syphilis, genital herpes, genital warts and HIV-AIDS.
2. Prevention: use condoms during sexual activity and avoid sex with multiple partners.
3. Prevention: get medical check-ups and treatment early, and do not share needles or personal items.
4. Prevention: maintain personal hygiene and seek treatment for the partner along with the affected person.

Teacher's Note:
a) Many STDs show no symptoms in the early stage, so check-ups matter.
b) Condoms reduce the risk but do not remove it completely.
c) Early treatment prevents serious problems such as infertility.

Very Short Answer type Questions

Question. Why is DNA copying an essential part of the process of reproduction?
Answer : Cell multiplication is essential for reproduction either as a means of multiplication in unicellular organisms or as a means of development of multicellular body from a single celled zygote. Cell multiplication cannot occur without DNA replication or DNA copying because each new cell must carry the full DNA complement.

Question. Where is DNA found in the cell?
Answer : Nucleus, plastids and mitochondria.

Question. State what type of method is used for growing jasmine plant.
Answer : Layering, a type of artificial method of vegetative propagation.

Question. Define sexual reproduction.
Answer : It is a mode of reproduction in which offspring are formed by the process of formation and fusion of gametes.

Question. What is the effect of DNA copying which is not perfectly accurate in the reproductive process?.
Answer : It produces mutations which give rise to useful, harmful and neutral variations in the progeny.

Question. Name the parts where germ cells of a flower are located.
Answer : Male — in anther of stamen.
Female — in ovule of carpel.

Question. List two functions of ovary of human female reproductive system.
Answer : 1. Formation of ova
2. Secretion of hormones estrogen and progesterone.

Question. List two unisexual flowers.
Answer : Water Melon, Papaya.

Question. Name the organs producing
(i) male germ cells / sperms and
(ii) female germ cells / ova respectively in humans.
Answer : (i) Testis
(ii) Ovary.

Question. What is DNA?
Answer : DNA or deoxyribonucleic acid is a self replicating biochemical that is carrier of genetic informationfor expression of hereditary traits and transfer to the next generation.

Question. Name the type of fission carried out by Amoeba.
Answer : Binary fission.

Question. Name the method by which Hydra reproduces commonly. Is this method sexual or asexual?
Answer : Hydra reproduces commonly by budding (also regeneration). It is a method of asexual reproduction.

Question. Name the type of reproduction mostly seen in unicellular organisms.
Answer : Asexual reproduction through cell division as binary fission, multiple fission, sporulation, budding.

Question. What happens when a mature Spirogyra filament attains considerable length?
Answer : The elongated mature filament of Spirogyra breaks to form smaller pieces or fragments. The fragments grow to form mature filaments. .

Question. Write the full form of IUCD.
Answer : Intra-uterine contraceptive device.

Question. Name any two types of asexual reproduction.
Answer : Fission, Spore formation.

Question. How does Plasmodium reproduce? Is this method sexual or asexual?
Answer : 1. Multiple fission,
2. Asexual method.

Question. What is fertilisation? Where does it occur in a human female?
Answer : Fertilisation is the fusion of male and female gametes to form diploid zygote. In human female, it occurs in ampulla part of fallopian tube.

Question. Name the method by which Spirogyra reproduces under favourable conditions. Is this method sexual or asexual?
Answer : 1. Fragmentation
2. Asexual method.

Short Answer type Questions

5. Explain how ovary functions both as reproductive organ as well as endocrine gland.
Answer : Reproductive Organ. Ovary produces ova, one every lunar month for possible fertilization and formation of foetus.
Endocrine Gland. Maturing ova or follicles present in ovary secrete oestrogen (= estrogen) while empty follicle develops into corpus luteum that secretes progesterone.

2. Compare the vegetative propagation of Bryophyllum and Money plant.
Answer : In Bryophyllum, vegetative propagation occurs through the agency of leaves that fall on moist soil. In Money Plant, vegetative propagation occurs with the help of stem cuttings bearing at least one leaf and its axillary bud. A single leaf of Bryophyllum can produce several plants. A leafy stem cutting of Money Plant forms only a single plant.

7. (a) Why are budding, fragmentation and regeneration considered as asexual type of reproduction?
(b) Which among the following reproduces by spore formation: Bryophyllum, Rhizopus, Hydra ?
Answer : (a) Asexual Reproduction: Budding, fragmentation and regeneration are all considered to be modes of asexual reproduction as they involve formation of new individuals from single parents without fertilization or fusion of gametes.
(b) Rhizopus.

3. (a) Where are the male germ cell and female gamete produced in a flower ?
(b) State the significance of variation in reproduction.
(c) Mention the principle of regeneration.
Answer : (a) Male Germ Cell (Male Gamete). Formed inside the pollen tube or pollen grain from generative cell.
Female Gamete (Oosphere). Inside embryo sac part of ovule.
(b) Significance of Variation in Reproduction
1. It provides individuality to each living organism,
2. It helps individuals in the struggle for existence,
3. Variation is a source of preadaptation.
(c) Principle of Regeneration: It is the ability of an individual to form lost or broken part, sometimes the entire individual from a piece of the parent body through dedifferentiation of mature cells and activity of reserve cells. The ability to form a new individual from a part of the body is well developed in simple animals like Hydra and Planaria. It is restricted to the formation of only broken parts in complex organisms.

4. (a) Name two bacterial STD infections.
(b) How do oral pills prevent pregnancy?
Answer : (a)
i. Gonorrhoea caused by bacterium Neisseria gonorrhoeae
ii. Syphilis caused by bacterium Treponema pallidum.
(b) Oral pills contain progestin (= progesterone) alone or in combination with estrogen. They prevent pregnancy by inhibition of ovulation, making uterine wall unsuitable for implantation alongwith unsuitable changes in cervical mucus and activity of fallopian tubes.

1. What is placenta? State its two roles during pregnancy.
Answer : Placenta is a spongy vascular structure formed by the joint activity of maternal and foetal tissues in the wall of uterus that connects foetus with uterus.
Roles:
1. Providing nutrition to the foetus.
2. Taking away wastes of the foetus.

6. What is the information source in the cell nucleus for making proteins. State the basic events in reproduction.
Answer : 1. Information Source. DNA
2. Basic Events in Reproduction. DNA replication, growth of cellular machinery and cell division.

Long Answer type Questions

8. Draw labelled diagram of
(a) Spore formation in Rhizopus
(b) Regeneration in Planaria.
Answer : (a)