CBSE Class 10 Science How do humans reproduce Sure Shot Questions Set 02

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ASSIGNMENT QUESTIONS SET - 2
CLASS X : CHAPTER - 8
HOW DO ORGANISMS REPRODUCE?

1. Mention the common mode of reproduction found in (i) Amoeba (ii) Planaria.

Answer:
(i) Amoeba reproduces by binary fission.
(ii) Planaria reproduces by regeneration.

Teacher's Note:
a) Binary fission splits one cell into two equal daughter cells.
b) Regeneration means regrowing a lost part into a complete new body.

2. Name any two types of asexual reproduction.

Answer: Budding and binary fission.

Teacher's Note:
a) Asexual reproduction needs only one parent and no gametes.
b) Budding is seen in Hydra and yeast; binary fission in Amoeba.

3. Define reproduction.

Answer: Reproduction is the biological process by which living organisms produce new individuals of their own kind.

Teacher's Note:
a) Reproduction ensures continuity of a species across generations.
b) Growth of an individual is not reproduction; it adds size, not new organisms.

4. Name two organisms that show asexual reproduction.

Answer: Amoeba and Hydra.

Teacher's Note:
a) Both are simple organisms with a single parent producing offspring.

5. How does Hydra reproduce? Name another organism that reproduces by a similar method.

Answer:
1. Hydra reproduces by budding.
2. A small bud develops on the parent body, grows into a new Hydra, and then detaches.
3. Yeast reproduces by a similar method, budding.

Teacher's Note:
a) The bud stays attached to the parent until it is fully formed.
b) Yeast is a unicellular fungus, so its bud is a single small cell.
c) Do not confuse budding with fragmentation, where the body breaks into pieces.

6. What is a spore?

Answer: A spore is a small, single-celled reproductive unit with a protective covering, which can develop into a new individual.

Teacher's Note:
a) Spores are usually light and produced in large numbers.
b) The thick wall of a spore protects it in unfavourable conditions.

7. Name two plants which reproduce through spores.

Answer: Moss and fern.

Teacher's Note:
a) Spore-producing plants lack flowers and seeds.
b) Spores are formed inside structures called sporangia.

8. Why is regeneration considered a method of reproduction?

Answer: In regeneration, a small fragment of the parent body grows into a complete new individual. This produces a new organism, which is why it is considered a method of reproduction.

Teacher's Note:
a) The key word is "new individual", not just repair of a damaged part.
b) Planaria is the standard example, where each piece becomes a full worm.

9. Which vegetative part is used in the propagation of Bryophyllum and mint?

Answer:
1. Bryophyllum is propagated by its leaf.
2. Mint is propagated by its stem.

Teacher's Note:
a) Buds on the leaf margins of Bryophyllum give rise to new plants.
b) Mint spreads through runners that grow along the ground.
c) Both are examples of vegetative propagation, not seed-based reproduction.

10. Name two types of layering.

Answer: Air layering and simple layering.

Teacher's Note:
a) In layering, a branch is bent to the soil or covered with moist soil while still attached to the parent.
b) Roots form on the covered part before the branch is cut off.

11. Name some plants where layering is used.

Answer: Jasmine and guava.

Teacher's Note:
a) Plants with flexible stems that root easily are suitable for layering.

12. Which technique would you use for propagating improved varieties of mango and rose?

Answer: Grafting (budding is also used for rose).

Teacher's Note:
a) Grafting joins a shoot of the desired variety onto a strong rootstock.
b) The new plant keeps the fruit or flower quality of the improved variety.
c) Seedlings from seeds would not reliably show the same traits.

13. Name various types of asexual reproduction.

Answer: Binary fission, multiple fission, budding, fragmentation, regeneration, spore formation and vegetative propagation.

Teacher's Note:
a) Each type has one parent and produces genetically similar offspring.
b) Multiple fission is seen in Plasmodium, which splits into many cells at once.

14. Mention the reproductive parts of a flower.

Answer: Stamens (male reproductive parts) and carpels or pistil (female reproductive parts).

Teacher's Note:
a) The stamen has an anther that produces pollen grains.
b) The carpel has a stigma, style and ovary.

15. Define fertilisation.

Answer: Fertilisation is the fusion of a male gamete with a female gamete to form a zygote.

Teacher's Note:
a) Fertilisation is also called syngamy.
b) The zygote is the first cell of the new organism.

16. What is self-pollination?

Answer: Self-pollination is the transfer of pollen grains from the anther to the stigma of the same flower or another flower of the same plant.

Teacher's Note:
a) Self-pollination does not need an external agent.
b) It reduces variation because the genetic material comes from one plant.

17. What is cross pollination?

Answer: Cross pollination is the transfer of pollen grains from the anther of a flower of one plant to the stigma of a flower of a different plant of the same species.

Teacher's Note:
a) Cross pollination usually needs an agent such as wind, water or insects.
b) It brings more variation in the offspring.

18. What are the agents of pollination?

Answer: Wind, water, insects, birds and other animals.

Teacher's Note:
a) Wind and insects are the most common agents.
b) Flowers pollinated by insects usually have bright petals and nectar.

19. Which process results in formation of zygote?

Answer: Fertilisation.

Teacher's Note:
a) Zygote is formed only when the male and female gametes fuse.

20. What grows to form a fruit?

Answer: The ovary grows to form the fruit.

Teacher's Note:
a) The ovary wall develops into the fruit wall.
b) Fruit formation is an example of the ovary changing after fertilisation.

21. What is carpel?

Answer: A carpel is the female reproductive part of a flower, made of a stigma, style and ovary. A group of carpels forms the pistil.

Teacher's Note:
a) Ovules are present inside the ovary of the carpel.
b) Do not confuse carpel with stamen, which is the male part.

22. Which parts of the flower transform into the seed and fruit?

Answer:
1. The ovule transforms into the seed.
2. The ovary transforms into the fruit.

Teacher's Note:
a) After fertilisation, the zygote in the ovule develops into the embryo of the seed.
b) The fruit protects the seeds and helps in their dispersal.

23. What are gonads?

Answer: Gonads are the primary sex organs that produce gametes. The testes in males and the ovaries in females are gonads.

Teacher's Note:
a) Gonads also secrete sex hormones.
b) Do not mix up gonads with the accessory reproductive organs.

24. What is puberty?

Answer: Puberty is the stage of life when the reproductive organs mature and the secondary sexual characters begin to appear. It usually starts around 10 to 14 years of age.

Teacher's Note:
a) Sex hormones trigger the changes seen at puberty.
b) The age of puberty differs between boys and girls.

25. When is ovum released in human female?

Answer: The ovum is released during ovulation, about mid-way through the menstrual cycle (around the 14th day of a 28-day cycle).

Teacher's Note:
a) Ovulation is the release of a mature ovum from the ovary.
b) The cycle length varies, so the exact day can differ from woman to woman.

26. What is endometrium?

Answer: Endometrium is the inner lining of the uterus. It is rich in blood vessels and supports the developing embryo.

Teacher's Note:
a) The endometrium thickens every month to prepare for a possible pregnancy.
b) If no fertilisation occurs, this lining breaks down and is shed as menstrual flow.

27. What is implantation?

Answer: Implantation is the attachment and embedding of the embryo (blastocyst) into the endometrium of the uterus.

Teacher's Note:
a) Implantation normally occurs about a week after fertilisation.
b) Without implantation, the embryo cannot get nourishment and pregnancy does not continue.

28. What is parturition?

Answer: Parturition is the process of delivery of the baby from the mother's uterus.

Teacher's Note:
a) Parturition is triggered by hormonal changes and strong uterine contractions.
b) It marks the end of pregnancy, lasting about nine months before it.

29. What is ovulation?

Answer: Ovulation is the release of a mature ovum from the ovary.

Teacher's Note:
a) Ovulation is controlled by hormones such as FSH and LH.
b) The released ovum travels into the fallopian tube, where fertilisation can take place.

30. Where are the ova produced in woman?

Answer: The ova are produced in the ovaries.

Teacher's Note:
a) A woman has two ovaries, one on each side of the uterus.

31. Name two sex hormones.

Answer: Oestrogen (female) and testosterone (male).

Teacher's Note:
a) Progesterone is another female sex hormone that maintains pregnancy.
b) Testosterone is secreted by the testes, while oestrogen is secreted mainly by the ovaries.
c) Sex hormones are not limited to one gender; both sexes make both types in small amounts.

32. What is the normal reproductive life in human female?

Answer: The normal reproductive life of a human female lasts from puberty, at about 12 years, to menopause, at about 45 to 50 years.

Teacher's Note:
a) Menopause is the permanent stopping of the menstrual cycle.
b) Ovulation and menstruation stop during menopause.

33. What are oral contraceptives?

Answer: Oral contraceptives are pills taken by mouth that contain hormones such as oestrogen and progesterone. They prevent pregnancy mainly by stopping ovulation.

Teacher's Note:
a) The pills must be taken regularly to be effective.
b) They do not protect against sexually transmitted diseases.

34. What is epididymis?

Answer: The epididymis is a coiled tube attached to each testis, where sperms mature and are stored.

Teacher's Note:
a) Sperms from the testis pass into the epididymis for maturation.
b) The epididymis leads into the vas deferens.

35. What are the functions of urethra?

Answer:
1. The urethra carries urine out of the body.
2. In males, it also carries semen (sperms) out of the body.

Teacher's Note:
a) In males, the urethra is a common passage for urine and semen.
b) Urine and semen never pass through the urethra at the same time.

36. What are the secondary sex characters in human male?

Answer:
1. Growth of beard and moustache.
2. Deepening of voice.
3. Broadening of shoulders and development of muscles.
4. Growth of hair on the chest, armpits and pubic region.

Teacher's Note:
a) Secondary sex characters are not directly involved in reproduction.
b) They develop under the influence of testosterone at puberty.
c) Voice change is due to growth of the larynx.

37. Why do testes lie outside the abdominal cavity?

Answer: Sperm production needs a temperature about 2 to 3 degrees Celsius lower than the body temperature. The scrotum keeps the testes outside the abdomen at this lower temperature.

Teacher's Note:
a) The scrotum muscles move the testes closer to or away from the body to control temperature.
b) High temperature inside the body would stop normal sperm formation.

38. When does puberty occur in human male and female?

Answer:
1. In girls, puberty occurs at about 10 to 12 years.
2. In boys, puberty occurs at about 13 to 14 years.

Teacher's Note:
a) Girls usually reach puberty earlier than boys.
b) Nutrition, health and heredity also influence the timing.

39. State the methods used for growing rose plants.

Answer: Rose plants are grown by stem cutting and by budding (grafting).

Teacher's Note:
a) A stem cutting with a few nodes can root in moist soil.
b) Budding gives improved varieties with better flowers.

40. State what type of method is used for growing jasmine plant.

Answer: Jasmine is grown by vegetative propagation, mainly by layering (and stem cutting).

Teacher's Note:
a) Layering keeps the branch attached to the parent until roots form.
b) The new plant is genetically identical to the parent.

41. Name the hormone, secretion of which is responsible for dramatic changes in appearance in girls when they approach 10-12 years of age.

Answer: Oestrogen.

Teacher's Note:
a) Oestrogen is secreted by the ovaries at puberty.
b) It causes breast development, growth of body hair and changes in body shape.

42. The organisms formed by asexual reproduction are considered as clones. Why? State the advantage of sexual reproduction over asexual reproduction.

Answer:
1. Asexual reproduction involves only one parent and DNA is copied without mixing, so offspring are genetically identical to the parent. Such identical offspring are called clones.
2. Sexual reproduction gives variation in the offspring, so some individuals can survive changes in the environment or new diseases.

Teacher's Note:
a) Clones have the same genetic make-up as the parent.
b) Variation is the main advantage of sexual reproduction.
c) Lack of variation makes a whole clone population vulnerable to the same threat.

43. What is the effect of DNA copying which is not perfectly accurate on the reproduction process?

Answer: Inaccurate DNA copying produces variations in the offspring. These variations create diversity in the population, which helps the species survive in a changing environment.

Teacher's Note:
a) Variations are the raw material for evolution.
b) Most small copying errors are neither harmful nor helpful.

44. How does the process of budding differ from the process of spore formation?

Answer:

Teacher's Note:
a) In budding, the bud is part of the parent body from the start.
b) Spores are separate, protected units that are released and germinate on their own.
c) Spore formation is usually a response to favourable conditions, so the spores can survive dry periods.

45. Name the type of asexual reproduction in : (a) Planaria (b) Rhizopus (iii) Spirogyra (iv) Hydra

Answer:
(a) Planaria: regeneration.
(b) Rhizopus: spore formation.
(iii) Spirogyra: fragmentation.
(iv) Hydra: budding.

Teacher's Note:
a) The part labels (iii) and (iv) follow (b) as printed in the question.
b) Fragmentation breaks a filament into pieces, and each piece grows into a new filament.

46. With the help of a diagram only show regeneration in Planaria. Regeneration is not possible in all types of animals. Why?

Answer:
1. Draw a Planaria and mark the cut lines across the body.
2. Each cut piece regrows the missing parts and develops into a complete worm.
3. Regeneration is not possible in all animals because complex animals have specialised cells and tissues that cannot regrow a whole body from a small piece.

Teacher's Note:
a) Planaria has a high capacity to regenerate because it has many undifferentiated cells.
b) Mammals can heal wounds but cannot regrow a lost limb or organ.
c) Draw the diagram with neat, labelled cut pieces.

47. How does the process of seed germination take place in plants? Describe in brief.

Answer:
1. The seed absorbs water and swells up.
2. The seed coat bursts open.
3. The radicle (embryonic root) grows downwards into the soil and forms the root.
4. The plumule (embryonic shoot) grows upwards and forms the stem and leaves.
5. The cotyledons supply food to the growing seedling until it can make its own food.

Teacher's Note:
a) Water and warmth are needed for germination; light is not always needed.
b) The radicle grows out before the plumule in most seeds.
c) Cotyledons are the seed leaves that store food.

48. Name the sex hormones secreted by male and female sex organs in human beings. State one function of each.

Answer:
1. Male: testosterone, secreted by the testes. It controls the development of male secondary sexual characters and sperm production.
2. Female: oestrogen, secreted by the ovaries. It controls the development of female secondary sexual characters and the menstrual cycle.

Teacher's Note:
a) Each hormone is secreted by a gonad, the testes or the ovaries.
b) Progesterone, secreted by the ovary, prepares the uterus for pregnancy.

49. State the mode of reproduction in following organisms : Earthworm, Frog, Rhizopus, Plasmodium.

Answer:
1. Earthworm: sexual reproduction (earthworms are hermaphrodites and cross-fertilise).
2. Frog: sexual reproduction (external fertilisation).
3. Rhizopus: asexual reproduction by spore formation.
4. Plasmodium: asexual reproduction by multiple fission.

Teacher's Note:
a) Earthworms have both male and female organs in one body.
b) Frogs lay eggs in water, where the sperms fertilise them outside the body.
c) Plasmodium divides into many daughter cells at once, which is multiple fission.

50. State in brief any two functions of copper-T used by some women.

Answer:
1. It releases copper ions that prevent sperms from fertilising the ovum.
2. It prevents the implantation of the embryo in the uterus.

Teacher's Note:
a) Copper-T is an intrauterine device placed inside the uterus.
b) It is a reversible method of contraception.

51. In what respect is the human male gamete different from the female gamete?

Answer:
1. The male gamete (sperm) is small and motile, with a tail for movement.
2. The female gamete (ovum) is large, non-motile and contains a large food reserve.

Teacher's Note:
a) Sperm is produced in large numbers, while only one ovum is released each month.
b) The food reserve in the ovum nourishes the early embryo.

52. What is reproduction? What are its two types? Which one of the two confers new characteristics on the offsprings and how?

Answer:
1. Reproduction is the biological process by which organisms produce new individuals of their own kind.
2. Its two types are asexual reproduction and sexual reproduction.
3. Sexual reproduction confers new characteristics on the offspring.
4. It involves two parents, and their genetic material combines during fertilisation. Copying errors in DNA and the mixing of genes during gamete formation also create new combinations of traits.

Teacher's Note:
a) Asexual reproduction copies one parent's DNA, so offspring are alike.
b) Mixing of genes from two parents is the key cause of variation.
c) Variation helps species adapt to changes in the environment.

53. What is binary fission? Draw a diagram to show binary fission in Amoeba.

Answer:
1. Binary fission is the division of a parent cell into two equal daughter cells.
2. In Amoeba, the nucleus divides into two first.
3. The cytoplasm then divides, and two daughter Amoebae are formed.

Teacher's Note:
a) Each daughter cell receives a copy of the nucleus.
b) Draw the nucleus clearly in the diagram, since examiners look for it.

54. What is regeneration? State a reason why a more complex organism cannot give rise to new individuals through this method.

Answer:
1. Regeneration is the ability of an organism to regrow a lost or damaged body part, or to form a new individual from a fragment of its body.
2. A more complex organism cannot give rise to new individuals this way because its cells are specialised and cannot form all the tissues of a whole body.

Teacher's Note:
a) Simple organisms like Planaria have many cells that are not yet specialised.
b) Specialised cells in complex animals lose the ability to form a whole new body.

55. Name the male and female gametes in animals. What is fertilisation and where does it take place in human females?

Answer:
1. The male gamete is the sperm and the female gamete is the ovum (egg).
2. Fertilisation is the fusion of a sperm with an ovum to form a zygote.
3. In human females, fertilisation takes place in the fallopian tube (oviduct).

Teacher's Note:
a) The zygote then divides and moves to the uterus.
b) Fertilisation needs the sperm to reach the ovum within about a day after ovulation.
c) Gametes carry only half the number of chromosomes of the body cells.

56. What is 'reproduction'? Mention the importance of DNA copying in reproduction.

Answer:
1. Reproduction is the process by which living organisms produce offspring similar to themselves.
2. DNA copying is important because it passes the hereditary instructions from parent to offspring.
3. The DNA copies also allow variation, which gives diversity in a population.

Teacher's Note:
a) DNA carries the information that decides the traits of an organism.
b) Accurate copying keeps the species alike, while small errors add variation.

57. Mention the information source of making proteins in the cell. What is the basic event in reproduction?

Answer:
1. The information for making proteins is stored in the DNA (genes).
2. The basic event in reproduction is the copying of DNA.

Teacher's Note:
a) Proteins are made by reading the DNA message through RNA.
b) Without DNA copying, a new cell cannot receive its genetic instructions.

58. Name one sexually transmitted disease each caused due to bacterial infection and viral infection. How can these be prevented?

Answer:
1. Bacterial infection: gonorrhoea (or syphilis).
2. Viral infection: AIDS (caused by HIV) (or genital warts).
3. Prevention: use condoms, avoid multiple sexual partners, and get regular medical check-ups and treatment.

Teacher's Note:
a) Bacterial infections can be cured with antibiotics, but viral infections often cannot.
b) Using a condom during sexual contact lowers the risk of both kinds.
c) Never share needles or razors, since blood can carry HIV.

59. Describe briefly four ways in which individuals with a particular trait may increase in a population.

Answer:
1. Individuals with the trait may survive better in the environment.
2. They may reproduce more successfully than others.
3. They may produce a larger number of offspring.
4. The trait is inherited by the offspring, so it spreads to the next generation.

Teacher's Note:
a) This process is called natural selection.
b) A trait must be heritable to spread through a population.
c) A trait that lowers survival will decrease in frequency over time.
d) Examiners look for the link between survival, reproduction and inheritance.

60. Why is it said that "sexual reproduction promotes diversity of characters in the offspring?

Answer:
1. Sexual reproduction involves two parents, so offspring receive a mix of genes from both.
2. Random fusion of gametes and the mixing of genes during gamete formation produce new combinations of traits.

Teacher's Note:
a) Every offspring receives a unique combination of genes.
b) Diversity is what allows a population to survive new diseases.

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

Answer: Pollination carries the pollen grains from the anther to the stigma. Without it, the pollen grains cannot reach the stigma, so the male gametes cannot reach the ovule and fertilisation cannot occur.

Teacher's Note:
a) Pollination is the transfer step, and fertilisation is the fusion step.
b) The pollen tube must grow from the stigma down to the ovule.

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

Answer: Bread mould needs water for its spores to germinate and for its hyphae to grow. A moist slice of bread provides this water, while a dry slice does not.

Teacher's Note:
a) Warmth and darkness also help mould growth, but moisture is the key factor here.
b) Bread mould is a fungus that feeds on the starch in the bread.

63. Leaves of Bryophyllum fallen on the ground produce new plants whereas the leaves of Jasmine do not, why?

Answer: Bryophyllum leaves have adventitious buds along their margins, and these buds grow into new plants when the leaf falls on moist soil. Jasmine leaves do not have such buds, so they cannot produce new plants.

Teacher's Note:
a) Adventitious buds arise from places other than the normal bud positions.
b) Jasmine is propagated by stem cuttings or layering, not by its leaves.

64. What is clone? Why do offspring formed by asexual reproduction exhibit remarkable similarity?

Answer:
1. A clone is a group of genetically identical individuals produced from a single parent.
2. Asexual reproduction involves only one parent and copies its DNA without mixing it with any other genetic material, so the offspring are very similar.

Teacher's Note:
a) Clones are identical in genes but can differ slightly due to environment.
b) Banana plants grown from suckers are an example of clones.

65. Write one disadvantage of asexual reproduction. When and how does multiple fission take place?

Answer:
1. Disadvantage: there is no variation among offspring, so all of them are equally affected by a change in environment or a disease.
2. Multiple fission takes place when conditions are favourable.
3. The nucleus divides repeatedly, and then the cytoplasm divides to form many daughter cells at the same time.

Teacher's Note:
a) Plasmodium, which causes malaria, reproduces by multiple fission inside the host.
b) Binary fission gives two cells, but multiple fission gives many cells at once.
c) A lack of variation can wipe out a whole population of clones.

66. State in brief the function of the following organs in the human female reproductive system. (a) Ovary (b) Fallopian tube (c) Uterus

Answer:
(a) Ovary: produces ova and female sex hormones (oestrogen and progesterone).
(b) Fallopian tube: receives the ovum from the ovary and is the site of fertilisation.
(c) Uterus: holds and nourishes the developing embryo and foetus until birth.

Teacher's Note:
a) The fallopian tube has cilia that push the ovum toward the uterus.
b) The uterine wall stretches greatly during pregnancy.
c) The ovary releases one ovum each cycle, usually alternating between the two sides.

67. Differentiate between : (a) Asexual and sexual reproduction. (b) Plumule and Radicle (c) Pollination and Fertilisation

Answer:

(a) Asexual and sexual reproduction

(b) Plumule and Radicle

(c) Pollination and Fertilisation

Teacher's Note:
a) In the plumule and radicle table, the radicle becomes the first root.
b) Pollination is external to the ovule, while fertilisation happens inside it.
c) Asexual reproduction is faster when conditions are stable, while sexual reproduction is slower but more varied.

68. Why is vegetative propagation practised for growing some types of plants? (b) Name the different parts of a flower that has germ cells. (c) List any two agents of pollination.

Answer:
(a) Vegetative propagation is practised for plants that produce few or no viable seeds, such as banana and rose, and to get plants that are identical to a parent with a good quality.
(b) The parts of the flower that have germ cells are the stamens (male germ cells in the pollen) and the carpels or pistil (female germ cells in the ovules).
(c) Wind and insects.

Teacher's Note:
a) Vegetative propagation gives faster flowering and fruiting than seeds.
b) Germ cells are the gametes, so look for the parts that make pollen and ovules.
c) Wind-pollinated flowers are usually small and do not have bright petals.

69. What happens to the pollen which falls on a suitable stigma? Explain.

Answer:
1. The pollen grain absorbs sugar and moisture from the stigma and germinates.
2. It forms a pollen tube that grows down through the style into the ovary.
3. The male gametes travel through the pollen tube to the ovule, where fertilisation takes place.

Teacher's Note:
a) A suitable stigma is one of the same species, so the pollen can germinate.
b) The pollen tube is the route that delivers the male gametes.
c) Germination of pollen is the first step after pollination.

70. List and describe in brief any three ways devised to avoid pregnancy.

Answer:
1. Barrier method: a condom is worn on the penis or inserted in the vagina to stop sperms from reaching the ovum.
2. Chemical method: oral contraceptive pills containing hormones prevent ovulation.
3. Intrauterine device: copper-T is placed in the uterus to stop sperms from fertilising the ovum and to prevent implantation.

Teacher's Note:
a) Condoms also protect against sexually transmitted diseases.
b) Pills must be taken at the same time daily to work well.
c) Copper-T is reversible, and it can be removed when a couple wants a child.

71. What are sexually transmitted diseases? Name four such diseases. Which one of them damages the immune system of human body?

Answer:
1. Sexually transmitted diseases are infections that spread mainly through sexual contact.
2. Four such diseases are gonorrhoea, syphilis, genital herpes and AIDS.
3. AIDS, caused by HIV, damages the immune system of the body.

Teacher's Note:
a) Genital warts (caused by HPV) is another common example.
b) HIV destroys the helper T-cells that fight infections.
c) Many such diseases can be treated early if they are diagnosed quickly.

72. Define grafting. Suggest any two advantages and disadvantages of grafting.

Answer:
1. Grafting is joining a shoot (scion) of one plant to the stem or root (stock) of another plant so that they grow as a single plant.
2. Advantages: the plant bears fruits of the desired quality, and it flowers and fruits earlier.
3. Disadvantages: it needs skill and care, and a disease of the stock can spread to the scion.

Teacher's Note:
a) The scion and stock must be closely related for the graft to join.
b) Grafting is common in mango, citrus and rose.
c) Failure of the graft union is a common problem, so the cut surfaces must match.

73. Name any two mechanical barriers of pregnancy. What are the benefits of using mechanical barriers during sexual act?

Answer:
1. Two mechanical barriers are the condom and the diaphragm.
2. They prevent sperms from entering the uterus, so pregnancy is avoided.
3. They also protect both partners from sexually transmitted diseases.

Teacher's Note:
a) A condom is worn on the penis or inserted in the vagina.
b) A diaphragm is a cap placed over the cervix.
c) Mechanical barriers have no hormonal side effects.

74. State in brief the functions of the following parts of the human male reproductive system : (i) Scrotum (ii) Testes (iii) Vas deferens

Answer:
(i) Scrotum: holds the testes outside the abdomen so that they stay at a temperature lower than the body.
(ii) Testes: produce sperms and the male sex hormone testosterone.
(iii) Vas deferens: carries sperms from the epididymis to the urethra.

Teacher's Note:
a) A lower temperature is needed for normal sperm formation.
b) The testes are made of many coiled seminiferous tubules.
c) The vas deferens is cut in a vasectomy, a method of male sterilisation.

75. State the role of ovary and fallopian tube in human body.

Answer:
1. Ovary: produces ova and secretes the female sex hormones oestrogen and progesterone.
2. Fallopian tube: carries the ovum from the ovary to the uterus, and fertilisation takes place here.

Teacher's Note:
a) Ovary is also a gonad, which means it produces gametes.
b) The fallopian tube is also called the oviduct.

76. What could be the possible reason for declining female to male sex ratio in our country. Suggest two measures to achieve 1:1 ratio.

Answer:
1. Possible reason: many families prefer a male child, so female foetuses are aborted after sex determination tests.
2. Measure 1: strictly enforce the law (PC and PNDT Act) that bans sex determination tests and sex-selective abortion.
3. Measure 2: create awareness and promote education and equal rights for girls.

Teacher's Note:
a) Dowry and social pressure add to the preference for sons.
b) A balanced sex ratio is important for social harmony and stable families.
c) Awareness campaigns work best when they reach rural families and parents.

77. What is the advantage of reproducing through spores?

Answer: Spores are small and light, so they can be carried over long distances by wind. Their thick wall protects them against harsh conditions until they find a favourable place to grow.

Teacher's Note:
a) Spores are produced in very large numbers.
b) A single parent can produce many new plants through spores, without a partner.

78. How does variation lead to the survival of species overtime?

Answer:
1. Variation gives different individuals different traits.
2. When the environment changes, some individuals with suitable traits survive.
3. These survivors reproduce and pass the useful traits to the next generation, so the species continues.

Teacher's Note:
a) Variation is the raw material on which natural selection works.
b) A population with no variation can be wiped out by one disease.

79. What will happen when : (a) A mature Spirogyra filament attains considerable length? (b) Planaria gets cut into two pieces?

Answer:
(a) The mature Spirogyra filament breaks into smaller fragments, and each fragment grows into a new filament.
(b) Each piece of Planaria regenerates the missing part and develops into a complete new Planaria.

Teacher's Note:
a) This method of fragmentation is common in filamentous algae.
b) Regeneration needs living cells from the cut part to form new tissues.

80. (a) Give reason : Regeneration is not the same as Reproduction. (b) State the mode of a asexual reproduction in Plasmodium

Answer:
(a) Regeneration usually only repairs or replaces a lost part of the same individual. Reproduction produces a new individual. Regeneration becomes reproduction only when an entire new organism develops from a fragment.
(b) Plasmodium reproduces asexually by multiple fission.

Teacher's Note:
a) Lizard tail regrowth is regeneration, not reproduction.
b) Multiple fission gives many daughter cells from one parent in a single event.

81. (a) Surgical methods can be used to create a block in the reproductive system for contraceptive purposes. Name such parts where blocks are created in : (i) males (ii) females (b) State any two reasons for using contraceptive devices.

Answer:
(a) (i) In males, the vas deferens is blocked (vasectomy).
(ii) In females, the fallopian tubes are blocked (tubectomy).
(b) 1. To prevent unwanted pregnancy.
2. To prevent sexually transmitted diseases.

Teacher's Note:
a) Surgical methods are permanent or nearly permanent.
b) Population control is another important reason for contraception.
c) Consult a doctor before choosing any method.

82. (a) What is vegetative propagation? (b) Write any two advantages of practising this method.

Answer:
(a) Vegetative propagation is the production of new plants from vegetative parts such as roots, stems or leaves, without seeds or spores.
(b) 1. The new plants are genetically identical to the parent, so they keep its good traits.
2. The new plants flower and fruit earlier than plants grown from seeds.

Teacher's Note:
a) Examples include sugarcane from stem pieces and Bryophyllum from leaves.
b) It is also useful for plants that do not produce viable seeds.

83. (a) Out of the following plants which two plants are reproduced by vegetative propagation? jasmine, wheat, mustard, banana (b) List any one advantage of practising this kind of propagation.

Answer:
(a) Jasmine and banana.
(b) The offspring are identical to the parent, so the good quality of the fruit or flower is preserved.

Teacher's Note:
a) Wheat and mustard are grown from seeds.
b) Banana is propagated from suckers.

84. (a) Identify the asexual method of reproduction in each of the following organisms : (i) rose (ii) yeast (iii) planaria (b) What is fragmentation? Name a multicellular organism which reproduces by this method.

Answer:
(a) (i) Rose: budding (or stem cutting).
(ii) Yeast: budding.
(iii) Planaria: regeneration.
(b) Fragmentation is the breaking of a multicellular body into pieces, and each piece grows into a new individual. Spirogyra is an example.

Teacher's Note:
a) Rose is commonly propagated by budding, which is a form of grafting.
b) Fragmentation is different from binary fission, which divides a single cell.
c) Spirogyra filaments break into smaller pieces that each grow into a new filament.

85. (a) How do the oral pills function as contraceptives? (b) The use of these pills may be harmful. Why?

Answer:
(a) 1. The pills contain oestrogen and progesterone, which stop the ovary from releasing an ovum.
2. They also thicken the cervical mucus, which blocks sperms, and make the endometrium unsuitable for implantation.
(b) The hormones in the pills can cause side effects such as nausea, weight gain, headache and blood clotting, so long-term use may be harmful.

Teacher's Note:
a) The pills act through hormones, not by a physical barrier.
b) Serious side effects are rare but can include blood clots.
c) Women with heart or blood pressure problems should check with a doctor first.

86. (a) Explain the terms : (i) implantation (ii) placenta (b) What is the average duration of human pregnancy?

Answer:
(a) (i) Implantation: the attachment and embedding of the embryo (blastocyst) in the endometrium of the uterus.
(ii) Placenta: a disc-shaped tissue in the uterine wall that connects the embryo to the mother's blood and supplies oxygen and food while removing waste.
(b) The average duration of human pregnancy is about 9 months, or 280 days.

Teacher's Note:
a) The placenta is connected to the embryo by the umbilical cord.
b) Blood of mother and foetus does not mix directly across the placenta.
c) Nine months is counted as 40 weeks from the last menstrual period.

87. (a) Why do testes located in scrotum outside the abdominal cavity? (b) What will happen to ovary and ovule after fertilization in angiospermic plants.

Answer:
(a) Sperm production needs a temperature about 2 to 3 degrees Celsius lower than the body temperature, and the scrotum keeps the testes at this lower temperature.
(b) After fertilisation, the ovary develops into the fruit and the ovule develops into the seed.

Teacher's Note:
a) The temperature of the body is about 37 degrees Celsius.
b) Seeds develop inside the fruit, which protects them.

88. In a bisexual flower inspite of the young stamens being removed artificially, the flower produces fruit. Give reasons. (a) Name the parts of the flower which ripens to form fruit and seed? (b) In the following diagram label A and B.

[Figure for Q88(b) is redrawn below.]

Answer:
1. Reason: even after the young stamens are removed, pollen grains from other flowers can reach the stigma through cross pollination by wind or insects.
2. The pollen grains then fertilise the ovules, so the flower forms a fruit.
(a) The ovary ripens to form the fruit, and the ovules ripen to form the seeds.
(b) A is the plumule (embryonic shoot) and B is the radicle (embryonic root).

Teacher's Note:
a) Removing stamens before they release pollen does not stop pollination from other flowers.
b) Ovary to fruit and ovule to seed is a key relationship in this topic.
c) The figure shows the two cotyledons of a seed joined to the embryo axis; the plumule (A) grows into the shoot and the radicle (B) grows into the root.

Very Short Answer type Short Questions

Question. Write the full expansion of HIV.
Answer : Human immuno-deficiency virus.

Question. What is vegetative propagation?
Answer : It is the formation of new plants from vegetative parts (e.g., stem, leaf, root, bud) of a parent plant.

Question. Name the life process of an organism that helps in the growth of its population.
Answer : Reproduction.

Question. In human female reproductive system where does fertilization occur?
Answer : In fallopian tube at ampulla—isthmus junction.

Question. When a cell reproduces, what happens to its DNA?
Answer : DNA replicates and forms its copy at the time of cell reproduction.

Question. List two functions performed by ovaries in a human female.
Answer : 1. Formation of ova
2. Secretion of hormones, estrogen and progesterone.

Question. Name the part of Bryophyllum where buds are produced for propagation.
Answer : Leaf notches.

Question. No two individuals are absolutely alike in a population. Why?
Answer : Due to presence of variations.

Question. Why is variation important for a species?
Answer : Variation provides adaptability to changing environment and increased fitness in the struggle for existence.

Question. Flow does Planaria reproduce? Is this method sexual or asexual?
Answer : 1. Transverse binary fission and regeneration
2. Asexual method.

Question. “Cell division is a type of reproduction in unicellular organisms”. Justify.
Answer : In unicellular organisms cell division is a mode of reproduction as it produces two individuals or daughters by division of the parent cell.

Question. Why is fertilization not possible without pollination?
Answer : Fertilization requires bringing of male gametes to the female gamete which is possible only when pollen grain is brought from the anther to the stigma in the process of pollination.

Short Answer type Short Questions

Question. (a) Define pollination. Why is it necessary for reproduction in flower bearing plants?
(b) Write one reason to explain why cross pollination is preferred over self pollination?
Answer : (a) Pollination is the transfer of pollen grains from anther to the stigma. It is essential because the male gametes of flower bearing plants are nonmotile. On stigma a pollen grain germinates and sends male gametes to embryo sac by means of a pollen tube.
(b) Cross pollination produces variations and maintains vigour of the plants.

Question. What are the advantages of sexual reproduction over asexual reproduction?
Answer : “significance of Sexual Reproduction”
a. Due to reshuffling of chromosomes and crossing over, sexual reproduction brings about variations in almost all characters so that no two individuals are similar. Variations are essential for recognition, individuality and competitiveness. They may not protect individuals under adverse conditions but survival of species depends upon pre-adaptive variations.
b. Better Adaptability. Increased variability due to sexual reproduction is helpful to organisms in better adaptability to changes in environment.
c. Vigour and Vitality. It maintains the vigour and vitality of the individuals.
d. Harmful Traits. Harmful traits are often kept suppressed because of reshuffling of gene pairs that occurs during gamete formation and fusion.
e. Near Uniformity of Population. Due to the flow of genes amongst individuals during sexual reproduction, the uniformity of population is maintained where there is a broad resemblance of all the individuals with one another.
f. Genetic changes brought about by sexual reproduction play an important part in evolution of new forms.

Question. What is the effect of DNA copying which is not perfectly accurate on the reproductive process? How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals?
Answer : (a) Inaccuracy in DNA Copying . Even small errors of DNA copying produce variations or mutations. Some of these mutations may be drastic as to kill the cells and stop the reproductive process. Others are minor and form the basis of varied traits.
(b) DNA Amount: The parents are diploid (2n) as each of them has two sets of chromosomes (DNAs). They form haploid (n) male and female gametes through the process of meiosis. The haploid gametes have one set of chromosomes (DNAs). During fertilization, one male gamete fuses with one female gamete. It restores the diploid (2n) chromosome/DNA number in the offspring that is formed from fusion product or zygote (2n).

Question. Draw diagrams to explain the regeneration that takes place in each of the body parts of Planaria when its body is cut into three pieces. Name any other organism in which a similar process can be observed.
Answer : (a) 

(b) Hydra.

Question. On cutting the body of an organism into many pieces, it was observed that many of these pieces developed as new individuals. Name the process and list two organisms in which this process may be observed. Draw a schematic diagram to illustrate the changes that are likely to be observed during the development of new individuals in any one of the organisms named.
Answer : (i) Regeneration,
(ii) Planaria, Hydra.

Question. Write one difference between asexual and sexual modes of reproduction. Which species is likely to have better chances of survival, the one reproducing asexually or the one reproducing sexually? Justify your answer.
Answer : ( a) Difference: Asexual reproduction is mono parental, with no gametes, no meiosis and very little variations. Sexual reproduction is generally biparental involving fusion of gametes, meiosis and lot of variations.
(b) Better Chances of Survival. Sexually reproducing.
Reason:
1. Due to reshuffling of chromosomes and crossing over, sexual reproduction produces variations in almost all characters,
2. Sexual reproduction maintains as well as improves vigour and vitality of the individuals,
3. Variability and vitality are helpful to organisms in better adaptability to environment.

Question. (a) How would you relate the following methods to asexual reproduction?
1. Binary fission
2. Spore formation?
(b) State any advantage of using sexual reproduction over asexual reproduction.
Answer : (a) Asexual reproduction is the formation of new individuals from a part of a single parent without formation and fusion of gametes.
1. In binary fission a fully grown unicellular individual divides into two similar individuals or daughters directly.
2. In spore formation a single cell or sac of the parent produces a number of reproductive bodies which get dispersed and form new individuals on germination. There is no meiosis or gamete formation in both the cases.
(b) Advantage of Sexual Reproduction. Sexual reproduction introduces variations and maintains the vigour and vitality of the individuals.

Question. List four points of significance of reproductive health in a society. Name any two areas related to reproductive health which have improved over past 50 years in our country.
Answer : 1. People can lead a safe, responsible and satisfying reproductive life.
2. Provides protection from catching STDs.
3. Advantage of small family, care of the children as well as their proper upbringing
4. Less mortality among the new borns.
5. Maintenance of proper health of the mother and lesser chances of maternal mortality.
Improvement:
1. Reduction in the rate of population growth.
2. Decrease in the spread of STDs.
3. Adoption of small family norm.

Question. Name the type of asexual reproduction demonstrated by the following organisms:
(a) Amoeba
(b) Rhizopus
(c) Planaria
(d) Plasmodium
(e) Spirogyra
(f) Bryophyllum.
Answer : (a) Amoeba. Binary fission.
(b) Rhizopus. Spore formation or sporulation
(c) Planaria. Regeneration
(d) Plasmodium. Multiple fission,
(e) Spirogyra. Fragmentation
(f) Bryophyllum. Vegetative reproduction by foliar buds.

Question. Prevention. Sexually transmitted diseases can be prevented by use of mechanical barriers, especially condoms.
(a) Name the following:
1. Thread like non-reproductive structures present in Rhizopus.
2. Blobs, that develop at the tip of the non-reproductive threads in Rhizopus.
(b) Explain the structure and function of structures released from the blobs in Rhizopus.
Answer : (a) 1. Hyphae (singular hypha).
2. Sporangia (singular sporangium).
(b) The structures released by blobs or sporangia are spores. Spores of Rhizopus are thick walled dark coloured and multinucleate. They are dispersed by air. After falling on a suitable substratum, each spore gives rise to a new mycelium.

Question. List six specific characteristics of sexual reproduction.
Answer : a. Biparental
b. Meiosis
c. Haploid gametes
d. Fertilization
e. Diploid zygote
f. Variations.

Question. (a) Define germination.

(b) From the given diagram identify the incorrectly labelled parts.
Answer : (a) Germination. Beginning of growth or sprouting of a propagule like spore, seed or bud is called germination. It requires a particular set of external and internal conditions.
(b) Incorrectly Labelled Parts:
1. Male germ cell
2. Pollen grain
3. Pollen tube
4. Ovule.

Question. What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.
Chromosomes are linear strands of DNA and associated proteins that occur in nucleus of eukaryotic cells, carry genes and function in transmission of hereditary information.
Answer : The parents are diploid (2n) as each of them has two sets of chromosomes (DNAs).
They form haploid (n) male and female gametes through the process of meiosis. The haploid gametes have one set of chromosomes (DNAs). During fertilization, one male gamete fuses with one female gamete. It restores the diploid (2n) chromosome/DNA number in the offspring that is formed from fusion product or zygote (2n).

Question. Explain how surgical methods used for men and women respectively help in contraception.
Answer : Reversible Sterilisation: It is surgical technique that prevents passage of sperms in males and ova in females. The technique is called reversible because by another surgical procedure the passage-way can be restored. Reversible sterilisation is otherwise permanent method of contraception. It is of two types, vasectomy in males and tubectomy in females.
1. Vasectomy: The two vasa deferentia of the male are blocked by cutting a small piece and tying the rest. This prevents passage of sperms from testes into semen.
2. Tubectomy: A portion of both the fallopian tubes is excised or ligated to block the passage of ovum.

Question. What is the importance of DNA copying during reproduction? Why are offspring formed by asexual reproduction genetically similar to their parents?
Answer : Importance of DNA Copying: DNA carries hereditary information not only for controlling cellular functions but also all the structural and functional traits of organism. It is because of the latter that single celled zygote is able to form the whole multicellular organism. During reproduction there is formation of new cells which must carry the same amount and type of hereditary information as present in the parent cell. This is accomplished by DNA copying, which occurs prior to each cell division. DNA copying is not error proof. Errors give rise to variations.
Offspring formed by Asexual Reproduction. Asexual reproduction is uniparental. The genetic material present in the offspring is unaltered copy of DNA present in the parent. Therefore, they are genetically similar to the parents.

Question. Give reason as to why the following processes are different from each other,
(a) Fission in Amoeba and Plasmodium.
(b) Regeneration and fragmentation.
(c) Binary fission and fragmentation.
Answer : (a) Under favourable conditions Amoeba multiplies by binary fission while Plasmodium multiplies by multiple fission.
(b)

Question. Budding is type of asexual reproduction used by Hydra.
(a) What is meant by asexual reproduction? How is it different from sexual reproduction?
(b) Name any other type of asexual reproduction used by Hydra. Define it.
Answer : Budding is a mode of asexual reproduction in Hydra as the propagules is a bud or outgrowth of somatic body of the animal.
(a) Asexual reproduction is the formation of new individuals from specialized or unspecialized somatic parts of a single parent.
Difference: Asexual reproduction is monoparental, with no gametes, no meiosis and very little variations. Sexual reproduction is generally biparental involving fusion of gametes, meiosis and lot of variations.
(b) 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.

Question. How does the uterus prepare itself and nurture the growing embryo? What happens when the egg is not fertilized?
Answer : Preparation: Under the influence of hormones from pituitary and growing Graafian follicle, the endometrium of uterus thickens, develops blood vessels and glands for nourishing the future embryo.
Nutrition for Growing Embryo. The contact region between embryo and endometrium grows into placenta. Placenta helps the embryo in obtaining nourishment (and oxygen) from blood sinuses of the uterus.
When Egg is not Fertilized: Glands present in the mucosa of uterine endometrium begin to degenerate. This sloughs off the endometrial lining, releasing a lot of mucus and blood. It is called menstruation. Menstruation lasts for 3-5 days.

Question. (a) A women had undergone surgical method for preventing unwanted pregnancies. Does this protect her from getting sexually transmitted diseases?
(b) How can AIDS be prevented?
Answer : (a) No, it does not prevent the coming together of body fluids during sex.
(b) Prevention of AIDS,
i. Use of barrier method of contraception like condom,
ii. Protection from getting infected, by blood contact like infected needles, syringes or transfusion,
iii. Proper sterilisation of dental equipment,
iv. Prevention of sexual contact with AIDS positive persons,
v. Prevention of pregnancy by AIDS positive patients.

Question. Rhizopus is an organism which reproduces by spore formation.
(a) What is meant by spore formation?
(b) What does the reproductive part or blob of Rhizopus contain?
(c) Why are these structures protected by thick walls?
Answer : ( a) Spore Formation. It is the formation of minute unicellular asexual reproductive disseminules which on germination give rise to new individuals.
(b) Blob or reproductive part of Rhizopus is sporangium. It contains spores.
(c) Thick Walls of Spores. Spores are dispersed by air currents. They have to face dry, hot, cold and other hostile conditions. Thick wall protects the spores from unfavourable environment.

Long Answer type Short Questions

Question. (a) Identify A, B and C in given diagram and write their functions,

(b) Mention the role of gametes and zygote in sexually reproducing organisms.
Answer : ( a) A-stigma: Reception of pollen grains and providing nutrients to pollen grains for their germination
B-pollen tube: Carrying of male gametes to inside the ovule for fertilization.
C-egg: Forms zygote and then embryo after fertilization.
(b) Gamete: It is haploid sex cell that brings traits in pure form from its parent for incorporation in the offspring. Zygote. Forms embryo.

Question. (a) Name the respective part of human female reproductive system
1. that produces eggs
2. where fusion of egg and sperm takes place and
3. where zygote gets implanted.
(b) Describe in brief what happens to the zygote after it gets implanted.
Answer : ( a)
1. Ovary
2. Fallopian tube (isthmus)
3. Uterus.
(b) Zygote/blastocyst after implantation grows to form embryo/foetus. The region of implantation forms placenta. The foetus remains attached to placenta by means of umbilical cord.
Through placenta, embryo is in contact with blood sinuses of the uterus for obtaining nutrients and elimination of wastes. The fully formed foetus undergoes parturition.

Question. (a) Draw a sectional view of human female reproductive system and label the following parts:
(b) 1. Where development of egg occurs
2. Where fertilization takes place.
Answer : (a)

Label
1. Ovary
2. Fallopian tube.
(b) 1. Endometrium thickens, becomes glandular and highly vascular. The contact region between embryo and uterine wall grows into placenta. Placenta helps the embryo in obtaining nourishment and oxygen from blood sinuses of the uterus. It also helps in transfer of wastes from embryo to the blood of the mother.
2. Glands present in the mucosa of uterine endometrium begin to degenerate. This sloughs off the endometrial lining, releasing a lot of mucus and blood. It is called menstruation. Menstruation lasts for 3-5 days.

Question. (a) Write the name of the human male reproductive organ that produces sperms and secretes a hormone.
Describe the changes the uterus undergoes
1. to receive the zygote
2. If zygote is not formed.
3. Name the hormone secreted and state its function.
(b) Write the site of fertilization and the part where the zygote gets implanted in the human female.
(c) State, in brief, how an embryo gets its nourishment inside the mother’s body.
Answer : (a) Testis. Hormone. Testosterone.
Function of Testosterone
1. Regulates sperm formation
2. Brings about puberty changes in males.
3. Maintains male secondary organs and traits.
(b) Site of Fertilization. Isthmus part of fallopian tube. Site of Implantation. Uterus.
(c) Nourishment of Embryo: Embryo gets nourishment from mother’s body with the help of placenta through a cord called umbilical cord. Placenta contains many finger-like villi from the chorion covering of the embryo. They occur in contact with blood sinuses of the mother present in the endometrial lining of uterus. All nutrients (glucose, amino acids, vitamins, etc.) diffuse from mother’s blood into villi and from there to embryo through the umbilical cord.

Question. (a) Write the function of placenta in human females,
(b) List four ways of preventing pregnancy. State two advantages of using such preventive methods.
Answer : (a) Placenta: It is a special double layered, spongy tissue connection between the foetus and uterine wall found in pregnant females. It has finger-like outgrowths or villi which are in contact with blood sinuses present in the uterine wall.
Role:
1. Attachment: Placenta attaches the foetus to uterine wall.
2. Villi: Placenta has finger-like outgrowths or villi which develop a large surface area for fixation and absorption.
3. Nutrients: Placenta picks up nutrients from mother’s blood and passes it to the blood of the foetus.
4. Waste Products: Waste products produced by the foetus passes out through the placenta into mother’s blood.
5. Gases: Foetus obtains oxygen supply from mother’s blood and eliminates carbon dioxide through placenta.
(b) Methods of Contraception:
1. Mechanical Barriers like condoms, cervical cap, diaphragm.
2. Oral Contraceptives or oral pills like Mala D, Saheli
3. Intrauterine Contraceptive Devices (IUCD) like loop, bow, Cu-T.
4. Surgical Methods like vasectomy in males and tubectomy in females.

Question. (a) Give an example each of a unisexual and a bisexual flower.
(b) Mention the changes a flower undergoes after fertilization.
How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals?
Answer : (a) Unisexual Flowers: Papaya.
Bisexual Flower: Mustard.
(b) DNA Amount: The parents are diploid (2n) as each of them has two sets of chromosomes
(DNAs). They form haploid (n) male and female gametes through the process of meiosis. The haploid gametes have one set of chromosomes (DNAs). During fertilization, one male gamete fuses with one female gamete. It restores the diploid (2n) chromosome/DNA number in the offspring that is formed from fusion product or zygote (2n).

Question. (a) Define fragmentation and regeneration,
(b) Can these two methods equated to be the same ? Answer with reason
(c) Give an example each of the organisms using the above methods.
Answer : (a) Fragmentation. It is breaking of an individual into two or more pieces with each piece growing to form the mature individual.
Regeneration. It is the ability of an individual to form lost or broken part, sometimes the whole individual.
(b) The two are not similar. Regeneration involves dedifferentiation, proliferation and differentiation to form lost parts. Fragmentation produces pieces where cells continue to divide resulting in growth of new individual. A repair is not involved.
(c) Regeneration. Hydra, Planaria. Fragmentation. Spirogyra, Marchantia.

Question. (a) Identify the leaf shown.

(b) Name the method used by the above leaf for reproduction.
(c) Give three advantages for the method used.
(d) Give two examples of plants which can be grown by this method.
Answer : (a) Bryophyllum
(b) Vegetative propagation
(c) 1. It is quicker method of propagation.
2. It gives rise to a genetically uniform propagation.
3. Good qualities of a variety can be maintained indefinitely.
(d) Sugarcane, Bougainvillea.

Question. Define the following processes:
(a) Fertilization
(b) Vegetative propagation
(c) Menstruation
(d) Regeneration
(e) Binary fission.
Answer : (a) Fertilization: The union of male gamete (sperm) with the female gamete (ovum) to form a diploid zygote is called fertilization.
(b) Vegetative Propagation: It is the formation of new plants from vegetative parts (e.g., stem, leaf, root, bud) of a parent plant.
(c) Menstruation: It is discharge of blood, mucus and broken pieces of endometrial lining in reproductively active females which occurs for 3-5 days at regular intervals of 28 days (lunar month). It occurs in response to non-fertilization of ovum and non-availability of progesterone hormone.
(d) Regeneration: It is ability of an individual to form lost or broken parts, sometimes the entire individual I from a piece of the parent body. The ability to form the whole individual from a piece of parent body is found only in simple animals like Hydra and Planaria. It does not occur in complex organisms like humans, birds, lizards etc. Here regeneration is limited to repair or regeneration of minor parts. It is because the tissues and organs are highly differentiated in complex animals.

Question. (a) Name the parts labelled A, B, C and D in the diagram.

(b) What is pollination? State its significance.
(c) How does fertilization occur in flowers? Name the parts of the flower that develop into
1. seed and
2. Fruit after fertilization.
Answer : (a) A—Pollen grain.
B—Pollen tube.
C—ovary.
D—Egg/oosphere.
(b) Pollination. The transfer of pollen grains from anther to the stigma of a flower is called pollination.
Significance- It carries the immobile pollen grains to the stigma for formation of male gametophyte and fertilization.
(c) After falling on a suitable stigma the pollen absorbs water and nutrients. It produces a pollen tube that grows through the style and reaches the ovary. Its tip contains a tube nucleus and two male gametes. The pollen tube enters an ovule, strikes against one synergid of the embryo sac and bursts open to release its contents. One male gamete fuses with the egg to form zygote while the other fuses with secondary nucleus to produce primary endosperm nucleus.
1. Seed—ovule,
2. Fruit—ovary.

Question. Justify the following statements :
(a) Variation is beneficial for the species over a period of time.
(b) New offspring produced are similar to their parents, but not identical
(c) Binary fission is different in Amoeba and Leishmania.
Answer : a) Many of the variations are pre-adaptations which have no immediate benefit to the individuals. However, they remain in the population. Whenever, environment undergoes a drastic change, the pre-adaptations present in some members of the population allow the latter to survive, grow and regain its former size. Therefore, it is not necessary that variations are beneficial to individuals developing them but can prove useful to the species.
(b) New offspring are similar to their parents because they have obtained the genetic traits from the same. They are, however, not identical because of chance separation, chance combination of chromosomes and recombination of genes due to crossing over.
(c) In Amoeba, binary fission can occur in any plane. In Leishmania the plane of division is vertical.

Question. (a) State in brief the function of the following organs in the human female reproductive system: Ovary, Fallopian tube, Uterus.
(i) What is menstruation? Why does it occur?
Answer : (a) 
i. Ovary: Formation of ova and secretion of hormones, estrogen and progesterone.
ii. Fallopian Tube: Passage of ovum, site for fertilization.
iii. Uterus: Implantation and nourishment of embryo.
(b) Menstruation:
It is discharge of blood, mucus and broken pieces of endometrial lining in reproductively active females which occurs for 3-5 days at regular intervals of 28 days (lunar month). It occurs in response to non-fertilization of ovum and non-availability of progesterone hormone.

Question. Explain what happens when :
(a) Testosterone is released in males
(b) Pollen grain falls on the stigma of the flower,
(e) Egg fuses with sperm cell,
(d) Planaria is cut into many pieces,
(e) Buds are formed at the notches of Bryophyllum leaf.
Answer : (a) Testosterone,
1. Regulates formation of sperms,
2. Puberty changes in boys.
3. Maintenance of secondary sexual characters in males.
(b) Pollen Grain. If pollen grain and stigma are compatible, the pollen grain absorbs water and nutrients from the stigma. It germinates and forms a pollen tube. Pollen tube passes into stigma and then style for reaching the ovary.
(c) Egg Fuses with Sperm Cell. The act is called fertilization. It produces a diploid zygote which later on grows into embryo.
(d) Cutting of Planaria. Each piece begins to regenerate, anterior end forms the anterior body parts, while posterior end gives rise to posterior body parts. Regeneration occurs with the help of stem cells and dedifferentiated cells (from differentiated ones).
(e) Bryophyllum Leaf. Buds present in the marginal notches of Bryophyllum leaf sprout and produce plantlets under suitable conditions. They help in vegetative multiplication.

Question. Differentiate between the following:
(a) Pollen tube and style,
(b) Fission in Amoeba and Plasmodium,
(c) Fragmentation and Regeneration,
(d) Bud of Hydra and Bryophyllum.
(e) Vegetative propagation and spore formation
Answer : (a) Pollen Tube and Style: Pollen tube is an outgrowth of pollen grain meant for carrying the male gametes to ovule. Style is a stalk-like structure of carpel (= pistil) that is meant for lifting the stigma above the level of ovary.
(b) Fission in Amoeba and Plasmodium: Under favourable conditions Amoeba multiplies by binary fission while Plasmodium multiplies by multiple fission.
(c) Fragmentation and Regeneration:
Fragmentation: It is breaking of an individual into two or more pieces with each piece growing to form the mature individual.
Regeneration: It is the ability of an individual to form lost or broken part, sometimes the whole individual.
(d) Bud of Hydra and Bud of Bryophyllum. In Hydra, bud is an outgrowth of the body which gets transformed into new animal that separates to lead an independent life. In Bryophyllum buds develop from the notches of the leaf. After falling on ground, the buds sprout and from plantlets.
(e) Vegetative Propagation and Spore Formation: In vegetative propagation new plants develop from specialised or unspecialised multicellular parts of the parent plant that function as propagules, e.g., Bryophyllum. Sugarcane. In spore formation, the individual parent produces unicellular reproductive bodies that get dispersed and form new individuals on germination, e.g., Rhizopus.

Question. (a) Write the functions of the following parts in human female reproductive system:
1. Ovary
2. Oviduct
3. Uterus.
(b) Describe the structure and function of placenta.
Answer : (a) 1. Ovary. Formation of ova and secretion of hormones, estrogen and progesterone.
2. Fallopian Tube. Passage of ovum, site for fertilization.
3. Uterus. Implantation and nourishment of embryo.
(b) Placenta: It is a special double layered, spongy tissue connection between the foetus and uternine wall found in pregnant females. It has finger-like outgrowths or villi which are in contact with blood sinuses present in the uterine wall.
Role:
1. Attachment: Placenta attaches the foetus to uterine wall.
2. Villi: Placenta has finger-like outgrowths or villi which develop a large surface area for fixation and absorption.
3. Nutrients: Placenta picks up nutrients from mother’s blood and passes it to the blood of the foetus.
4. Waste Products: Waste products produced by the foetus passes out through the placenta into mother’s blood.
5. Gases: Foetus obtains oxygen supply from mother’s blood and eliminates carbon dioxide through placenta.

Question. (a) What is vegetative propagation ? List with brief explanation three advantages of practising this process for growing some types of plants.
(b) Select two plants from the following which are grown by this process: Banana, Wheat, Mustard, Jasmine, Gram.
Answer : (a) Vegetative propagation is the formation of new plants by using vegetative parts of a parent plant as propagules e.g., stem (Sugarcane, Bougainvillea, Potato), root (Sweet
Potato, Dahlia), leaf (Bryophyllum), bud (Agave).
Advantages:
1. It is the only known method of multiplication of seedless plants like Banana and Sugarcane.
2. It is a quicker method as vegetatively reproduced plants bear flowers and fruits earlier than plants raised through seeds.
3. All the individual plants are clones of one another and their parent so that the crop is genetically uniform.
4. Good quality of a variety can be maintained indefinitely.
(b) Banana, Jasmine.