Reproduction

NCERT Exemplar Solution: Short Answer Type Question

Question: 28. In a bixesual flower inspite of the young stamens being removed artifically, the flower produces fruits. Provide a suitable explanation for the above situation.

Answer: In bixesual flower, when young stamens are removed, but pistil is intact. Cross–pollination has occurred leading to fertilization and formation of fruit.

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

Answer: Yes, because it results in the formation two daughter cells or individuals. It results in the production of more individuals of the organisms.

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

Answer: Clone is a population of genetically identical individuals. Offsprings formed by asexual reproduction possess exact copies of parental DNA or parental genotype, hence they exhibit remarkable similarity.

Question:31. Explain how, offspring and parents of organism reproducing sexually have the same number of chrosomes.

Answer: During sexual reproduction, gamets are formed as a result of meiosis cell division, hence the number of chromosomes will become half in the gamets. During fertilization in sexual reproduction, when male and female games fuse, the original number of chromosomes (as in the parent) is restored in offspring.

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

Answer: Sugar provides energy for sustaining all life activities in yeast. In water it fails to reproduce because of inadequate energy inc cells.

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

Answer: Moisture is an important factor for the growth of hyphae. Moistened bread slice offers both moisture and nutrients to the bread mould, hence it grows profusely. Dry slice of bread offers nutrient but not moisture hence hyphae fail to grow.

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

Answer: Progeny formed as a result of sexual reproduction shows variations because:

(a) Sexual reproduction involves two parents with different sets of characters.

(b) The gene combination are different in gametes.

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

Answer: Regenerated parts of figures D and E are shown here:

Question: 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 organism have more number of chromosomesl/cells?

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

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

Anwer: (a) No, there is no relationship between size of organism and its chromosome number.

(b) No, process of reproduction follows, a common pattern and is not dependent on the number of chromosome.

(c) Yes, since the major component of chromosome is DNA, if there are more chromosomes in a cell. The quantity of DNA will also be more.

Question: 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 chromosomes in the zygote?

Answer: Number of chromosomes in zygote is 48.

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

Answer: In flowers fertilization requires both male and female gametes.

If pollination does not occur, male gamete is not available hence fertilization cannot take place.

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

Answer: Yes, the constancy is maintained because cells in all these three structures undergo only mitotic divisions.

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

Answer: Zygote is located inside the ovule which is present in the ovary.

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

Answer: In a repeoducing of dividing cell, DNA creastes its two copies by making use of cellular machinery, this DNA passes from one generation to the next. Copying of DNA takes place with consistency. This consistency leads to stability of species.

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

Answer: General growth refers to different types of developmental processes in the body like increase in height, weight gain, changes in shape and size of the body, but sexual maturation is specific to changes reflected puberty like in males cracking voice, development of facial hair, pubic hair, enlargement of external genital organs and in females enlargement of breasts, pubic and axillary hairs, onset of mensural cycle.

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

Answer: Sperm are produced in the seminiferous tubules of testes from where they pass through vasa efferentia into epididymis. At the time of ejaculation, the sperms are first passed through vas deferens, enter ejaculatory duct where they receive secretion of associated glands like prostate and seminal vesicle to form semen; Secretion of these glands provide nutition do the sperms and also facilitate transport.

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

Answer: If fertilization does not take place the hormonal secretion is reduced, as a result the blood supply to the uterine wall is cut off and the thick and spongy lining of uterus slowly breaks, the glands present in mucosa of uterine edometrium begin to degenerate. The sloughs off the endometrial lining, releasing a lot of mucus and blood. It is called menstruation. It lasts for 3 to 5 days.

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

Answer: The uterine wall thickens, becomes glandular and highly vacular. A special tissue called placenta develops which connects embryo to the uterine wall.

Placenta helps in physiological exchange between uterus and foetus, that is it helps the embryo in obtaining nourishment and oxygen from maternal blood, and transfer of carbon dioxide and metablic wastes from embryo to maternal blood.

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

Answer: Mechanical barriers e.g., condoms and diaphragm prevent the passage of sperms into vaginal tract, hence prevent fertilization.

These also prevent transmission of infection during sexual act.

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

(a) Production of egg

(b) Site of fertilisaiton

(c) Site of implantation

(d) Entry of sperms

Answer:

(a) Production of egg – ovary

(b) Site of fertilization – Fallopian tube

(c) Site of implantation – Uterus

(d) Entry of sperm – Vagina

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

Answer: The ratio is 1 : 2

Sperms are genetically of two types; sperms have either X chromosome or Y chromosome, where an ova will always have and X chromosome.