NCERT Exemplar problems for Class 10 Science Chapter 8 How do Organisms Reproduce ?

Short Answer Questions

Question.1 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. Removal of stamens of a bisexual flower will not affect pollination of its intact pistil and formation of fruit. Cross-pollination has occurred leading to fertilisation.

Question. 2 Can you consider cell division as a type of reproduction in unicellular organism? Give one reason.
Answer. Yes, because cell division in a unicellular organism results in the formation of two daughter cells which means it produces more individuals of the organisms.

Question.3 Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes.
Answer. The parents are diploid (2n) as each of them has two sets of chromosomes. They form haploid (1n) male and female gametes through the process of meiosis. The haploid gametes have one set of chromosomes. Since, these two gametes fuse during fertilisation, the original number of chromosomes is restored in the offspring.

Question. 4 Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this.
Answer. Energy is essential for any activity in living organisms. Sugar provides this energy for sustaining all life activities in yeasts. In water, it fails to reproduce because of inadequate energy in its cells. So, colonies of yeast fail to multiply in water but multiply in sugar solution.

Question. 5 Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?
Answer.Bread mould require moisture and nutrients for its growth. A moist slice of bread contains both moisture and nutrients hence, it grows profusely as compared to a dry slice of bread which contains only nutrients but no moisture.

Question. 6 Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.
Answer.

1. In sexual reproduction, two parents have different sets of characters.
2. Gene combinations are different in gametes.

Question. 7 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. The number of chromosomes in the female gamete is 24. The number of chromosomes in the zygote is 48.

Question. 8 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. Yes, the chromosome number of zygote, embryonal cells and adult of a particular organism is always constant.
The constancy is maintained because the cells in all these three structures undergo only mitotic divisions.

Question. 9 How are general growth and sexual v maturation different from each other?
Answer. General growth is the growth of different types of developmental process in the body like increase in height, weight gain, changes in shape and size of the body.
Sexual maturation is a set of changes in body of an individual at puberty like cracking of voice, new hair patterns, development of breast in female, etc.

Question. 10 What would be the ratio of chromosome number between an egg and its zygote? How is the sperm genetically different from the egg?
Answer. The ratio of chromosome number between an egg and its zygote is 1: 2.
Sperm is genetically different from the egg in the way that it contains either X or Y chromosome whereas, an egg always contains an X chromosome.

Long Answer Questions

Question. 11 Distinguish between a gamete and zygote. Explain their roles in sexual reproduction.
Answer.

Role of Gamete in sexual reproduction — Gamete is the sex or germ cell specialised to take part in sexual reproduction. Fusion of male gamete with a female gamete produces a zygote. Role of Zygote in sexual reproduction — Zygote develops into embryo that later forms the new individual.

Question. 12 What is placenta? Mention its role during pregnancy?
Answer. Placenta is a special tissue that develops between the uterine wall and the embryo (foetus).
The role of placenta during pregnancy is as follows:

1. Placenta attaches the foetus to uterine wall.
2. It possesses villi that increases the surface area for fixation and absorption.
3. It facilitates the passage of nutrition and oxygen to embryo from mother through blood.
4. Waste substances produced by embryo (foetus) are removed through placenta into mother’s blood.

Question. 13 How does fertilisation take place? Fertilisation occurs once in a month. Comment.
Answer. Fertilisation takes place in the following ways:

1. The sperm enters through the vaginal passage during sexual intercourse and moves upward.
2. Egg released from the ovary reaches the oviduct.
3. Sperm encounters egg in the oviduct and fertilisation takes place. Fertilisation occurs once in a month because egg is released by female ovary once every month in the middle of menstrual cycle.