CBSE Class 10 Science How Do Organisms Reproduce VBQs Set 03

Question. 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 as its pistil is inact. Therefore, formation of fruit will take place as transfer of pollen grains from the anther of another flower to the stigma of flower will take place which causes cross-pollination.

Question. 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. For example, Amoeba is a simple unicellular organism that splits into two daughter cells.

Question. What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?
Answer: Clone is the exact genetic replica of another individual. All the offsprings formed from a parent through asexual method of reproduction are same. The remarkable similarity of asexually produced daughter individuals is due to genetic similarity as they possess exact copies of DNA of their parent.

Question. 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. 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. Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.
Answer: (i) In sexual reproduction, two parents have different sets of characters. (ii) Gene combinations are different in gametes.

Question. 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 contents. Justify.
Answer: (a) No, there is no correlation between chromosome number and size of the individual. (b) No, chromosome number does not affect reproduction. Reproduction depends on environmental factors like nutrients availability, water source, etc. (c) Yes, since major component of chromosome is DNA, if there are more chromosomes in a cell means more DNA.

Question. 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. Why cannot fertilisation take place in flowers if pollination does not occur?
Answer: Pollination is essential for bringing the male gametes to meet the female gamete. Only after the arrival of pollen grains on stigma and entry of pollen tube into ovary, male gamete fuse with female gamete. In absence of pollination, there will be no male gamete to bring about fertilisation.

Question. 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. Where is the zygote located in the flower after fertilisation?
Answer: Zygote is located inside the ovule which is present in the ovary part of the pistil.

Question. Reproduction is linked to stability of population of species. Justify the statement.
Answer: In reproduction, DNA passes from one generation to the next. The copying of DNA takes place with consistency but with minor variations and this consistency leads to stability of species.

Question. How are general growth and sexual 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. Reproductive organs are less active during this phase. Sexual maturation is a set of changes in the body of an individual at puberty like cracking of voice, new hair patterns, development of breast in female, etc.

Question. Trace the path of sperm during ejaculation and mention the gland and their functions associated with the male reproductive system.
Answer: The sperms comes out from testis into the vas deferens and then pass through urethra before ejaculation. The secretions of seminal vesicle and prostate glands provide nutrition to the sperms and also facilitate their transport.

Question. What changes are observed in the uterus if fertilisation does not occur?
Answer: The thick and spongy lining of the uterus slowly breaks and comes out through the vagina as blood and mucous if fertilisation does not occur. This is known as menstruation and it lasts for about two to eight days.

Question. What changes are observed in the uterus subsequent to implantation of young embryo?
Answer: The changes observed in the uterus subsequent to implantation of young embryo are — The uterine wall thickens and is richly supplied with blood. The contact region between embryo and uterine wall grows into placenta which provides nourishment and oxygen to the embryo. Waste material of developing embryo are removed by transferring them into the mother’s blood through the placenta.

Question. What are the benefits of using mechanical barriers during sexual act?
Answer: The benefits of using mechanical barriers during sexual act are — (i) Prevention of pregnancy – Mechanical barriers like condom prevents the sperms from reaching the egg, which is an effective method to avoid pregnancy. (ii) Non-transmission of Infections – There is no transfer of diseases from the infected person to non-infected person.

Question. 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 \( 1 : 2 \). Egg is produced through meiosis and therefore, contains half number of chromosomes of its parent cell whereas zygote is the product of fertilization between male and female gamete and thus, contains double the number of chromosomes with respect to egg. 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.

Question. Distinguish between a gamete and zygote. Explain their roles in sexual reproduction.
Answer: Differences between:
Gamete:
(i) It is a germ cell that takes part in fertilisation.
(ii) There are two types of gametes – male and female.
(iii) A gamete has haploid or \( 1n \) chromosome number.
(iv) A gamete carries characteristics of only one parent.
(v) Gamete is the last cell of its generation.

Zygote:
(i) It is a product of fertilisation.
(ii) Zygote is of one type.
(iii) Zygote has diploid or \( 2n \) chromosome number.
(iv) It carries characteristics of both the parents.
(v) It is the first cell of new generation.

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. How does fertilisation take place? Fertilisation occurs once in a month. Comment.
Answer: Fertilisation takes place in the following ways:
(i) The sperm enters through the vaginal passage during sexual intercourse and moves upward.
(ii) Egg released from the ovary reaches the oviduct.
(iii) 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.

Self-Evaluation Test

Question. Gynoecium is
(a) Differentiated into ovary, style and stigma
(b) Differentiated into filament and anther
(c) Male reproductive part
(d) Female reproductive part
Answer: (a) Differentiated into ovary, style and stigma

Question. Double fertilisation is a characteristics of
(a) Angiosperms
(b) Pteridophytes
(c) Gymnosperms
(d) Bryophytes
Answer: (a) Angiosperms

Question. Fertilisation of ovum takes place in
(a) Ovary
(b) Fallopian tube
(c) Cervix
(d) Uterus
Answer: (b) Fallopian tube

Question. The period of development of foetus in the uterus is known as:
(a) Cleavage
(b) Gestation
(c) Implantation
(d) Menstruation
Answer: (b) Gestation

Question. In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion. (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion. (c) Assertion is true but the Reason is false. (d) The statement of the Assertion is false but the Reason is true. Assertion: Banana reproduce from roots.
Reason: Plants which lost the capability to produce viable seeds reproduce by vegetative method
(a) A
(b) B
(c) C
(d) D
Answer: (d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: In male reproductive system, transport of sperms take place in a fluid which also provide nutrition.
Reason: Protective glands and seminal vesicles secrete in the vas deferens
(a) A
(b) B
(c) C
(d) D
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Describe the role of fallopian tube in the female reproductive system.
Answer: The fallopian tube (or oviduct) is the site where fertilisation of the egg by the sperm takes place. It also serves as a passage that carries the released egg from the ovary towards the uterus.

Question. Why is DNA copying an essential part of the process of reproduction?
Answer: DNA copying is essential because it ensures the transfer of genetic information from the parent to the offspring. It provides the necessary blueprint for the body design of the new individuals, ensuring they resemble their parents while allowing for small variations essential for evolution.

Question. ‘Grafting is a common method of obtaining a superior plant from two different plants’. Explain.
Answer: Grafting involves joining the stem (scion) of a plant with superior qualities (like fruit flavor) onto the root system (stock) of another hardy or disease-resistant plant. This allows the combined plant to have the best traits of both, such as high-quality produce and a strong root system.

Question. Illustrate the following with the help of suitable diagram: (a) Binary Fission in Amoeba (b) Leaf of Bryophyllum with buds
Answer: (a) [A diagram would show an Amoeba cell elongating, the nucleus dividing into two, followed by the cytoplasm splitting to form two identical daughter cells]. (b) [A diagram would show a leaf of Bryophyllum with tiny plantlets or adventitious buds growing along its marginal notches].

Question. What is pollination? How does it occur in plants? How does pollination lead to fertilisation?
Answer: Pollination is the transfer of pollen grains from the anther of a flower to the stigma. It can occur within the same flower (self-pollination) or between different plants (cross-pollination) via agents like wind, water, or insects. Once on the stigma, a pollen grain germinates to form a pollen tube that carries male gametes to the ovary, where they fuse with the egg cell, leading to fertilisation.

Creation of two new cells from one involves copying of the DNA as well as of the cellular apparatus. The DNA copying mechanism, cannot be absolutely accurate, and the resultant errors are a source of variations in populations of organisms. Every individual organism cannot be protected by variations, but in a population, variations are useful for ensuring the survival of the species. It would therefore make sense if organisms come up with reproductive mode that allows more and more variation to be generated.

Question. Write one significance of reproduction.
Answer: Reproduction is essential for the continuation of a species over generations, preventing its extinction.

Question. What is the advantage of sexual mode of reproduction?
Answer: The primary advantage of sexual reproduction is that it promotes genetic variation among offspring, which provides a population with better adaptability to changing environmental conditions.

Question. Write one advantage of asexual mode of reproduction. Or How do organisms reproduce by regeneration?
Answer: An advantage of asexual reproduction is that it is a rapid and energy-efficient process that requires only a single parent. Or In regeneration, if an organism like Planaria is cut into pieces, each piece has specialized cells that can proliferate and grow to recreate the entire missing body parts, eventually forming a complete new individual.