Q.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.
Ans. In a bisexual flower, even if the young stamens are removed artificially, the flower can still produce fruit because the female reproductive parts, such as the ovary and stigma, are intact. The ovary contains the ovules, which can be fertilized by pollen grains, leading to the formation of seeds and fruits.
Q.2 Can you consider cell division as a type of reproduction in unicellular organism? Give one reason.
Ans. Cell division in unicellular organisms can be considered a type of reproduction because it results in the formation of new individuals. Unicellular organisms reproduce by dividing into two daughter cells through processes like binary fission or budding.
Q.3 What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?
Ans. A clone is a group of genetically identical individuals derived from a single parent organism. Offspring formed by asexual reproduction exhibit remarkable similarity because they are genetically identical to the parent organism. Asexual reproduction involves the production of offspring from a single parent, without the involvement of gametes or genetic recombination.
Q.4 Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes?
Ans. Offspring and parents of organisms reproducing sexually have the same number of chromosomes because during sexual reproduction, the gametes (sperm and egg) produced by the parents undergo a process called meiosis. Meiosis ensures that the number of chromosomes in the gametes is halved, allowing for the fusion of gametes during fertilization to restore the original chromosome number in the offspring.
Q.5 Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this.
Ans. Colonies of yeast fail to multiply in water but multiply in a sugar solution because yeast cells require a source of energy to grow and multiply. Sugar solution provides the necessary carbohydrates for yeast cells to undergo cellular respiration and produce energy for growth and reproduction.
Q.6 Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?
Ans. Bread mold grows profusely on a moist slice of bread rather than on a dry slice of bread because moisture is essential for the growth and reproduction of mold spores. Moist conditions provide an environment conducive to the germination of mold spores and the growth of mold hyphae, allowing bread mold to thrive and multiply.
Q.7 Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.
Ans.
Two reasons for the appearance of variations among the progeny formed by sexual reproduction are:
Genetic recombination: During meiosis, genetic material from both parents is shuffled and recombined, leading to genetic variation in the offspring.
Random assortment of chromosomes: During meiosis, homologous chromosomes assort independently into gametes, resulting in different combinations of genetic material in the offspring.
Q.8 Would a Planaria cut vertically into two halves regenerate into two individuals? Complete Figure 8.2 D and E by indicating the regenerated regions.
Ans. Yes Planaria cut vertically into two halves can regenerate into two individuals.
Q.9 From the internet, gather information about the chromosome numbers of five animals and five plants. Correlate the number with the size of organism and answer the following questions.
(a) Do larger organisms have more number of chromosomes/cells?
(b) Can organism with fewer chromosomes reproduce more easily than organisms with more number of chromosomes?
(c) More the number of chromosomes/cells greater is the DNA content. Justify.
Ans.
(a) The number of chromosomes in an organism is not directly correlated with its size. Some small organisms may have more chromosomes than larger organisms, and vice versa.
(b) Organisms with fewer chromosomes may not necessarily reproduce more easily than those with more chromosomes. Reproduction depends on various factors, including genetic compatibility, environmental conditions, and reproductive strategies.
(c) The number of chromosomes does not necessarily correlate with the amount of DNA content. While more chromosomes may result in a higher DNA content, the DNA content can vary greatly among organisms with different chromosome numbers.
Q.10 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?
Ans. In the tobacco plant, the female gamete likely has 24 chromosomes, similar to the male gamete. When the male and female gametes fuse during fertilization, the zygote formed would have 48 chromosomes.
Q.11 Why cannot fertilisation take place in flowers if pollination does not occur?
Ans. Fertilization requires the fusion of male and female gametes. Without pollination, there would be no transfer of pollen containing male gametes to the female reproductive structures of the flower, making fertilization impossible.
Q.12 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?
Ans. The chromosome number of the zygote, embryonal cells, and adult of a particular organism can vary. However, in sexually reproducing organisms, the chromosome number is generally maintained throughout different stages of development through processes like meiosis, which ensures that gametes have half the chromosome number of somatic cells.
Q.13 Where is the zygote located in the flower after fertilization?
Ans. After fertilization, the zygote is located within the ovule of the flower. The ovule is contained within the ovary of the flower, where fertilization occurs.
Q.14 Reproduction is linked to stability of population of a species. Justify the statement.
Ans. Reproduction ensures the stability of the population of a species by producing offspring that replace individuals lost through death or other factors. It maintains genetic diversity within the population, which is important for adapting to changing environmental conditions and avoiding extinction.
Q.15 How are general growth and sexual maturation different from each other?
Ans. General growth refers to the overall increase in size and development of an organism’s body, including its organs and tissues. Sexual maturation, on the other hand, specifically refers to the development of reproductive structures and the ability to reproduce.
Q.16 Trace the path of sperm during ejaculation and mention the gland and their functions associated with the male reproductive system.
Ans. During ejaculation, sperm travel through the vas deferens, where they mix with fluids from the seminal vesicles, prostate gland, and bulbourethral glands. These fluids provide nutrients, buffer the acidic environment of the urethra, and aid in the motility and protection of sperm. Eventually, sperm are ejaculated through the urethra during ejaculation.
 Q.17 Trace the path of sperm during ejaculation and mention the gland and their functions associated with the male reproductive system.
Ans. Sequence of organs in the male reproductive system for transport of sperms is testis → epididymis → vasdeferens → prostate→ urethra.
| Glands associated with male reproductive system | Function |
| Testes | Secretion of testosterone |
| Prostate gland | Makes the medium of semen alkaline |
| Seminal vesicle | Addition of fluid content to semen |
| Cowper’s gland | Urethra lubrication and neutralizes acidic traces of urine. |
Q.18 What changes are observed in the uterus if fertilisation does not occur?
Ans. If fertilization does not occur, the lining of the uterus, known as the endometrium, sheds during menstruation. This shedding results in the expulsion of the endometrial tissue and blood from the uterus, leading to menstrual flow.
Q.19 What changes are observed in the uterus subsequent to implantation of young embryo?
Ans. After implantation of the young embryo, the endometrium undergoes changes to support the developing embryo. These changes include the thickening of the endometrial lining, increased blood supply to nourish the embryo, and the development of structures like the placenta to facilitate nutrient and waste exchange between the mother and the embryo.
Q.20 What are the benefits of using mechanical barriers during sexual act?
Ans. Mechanical barriers, such as condoms, help prevent the transmission of sexually transmitted infections (STIs) and unwanted pregnancies. They provide a physical barrier that prevents the exchange of bodily fluids between sexual partners, reducing the risk of STIs. Additionally, they offer a non-hormonal method of contraception, giving individuals control over their reproductive health without altering hormonal balances.
Q.21 In the given Figure 8.3 label the parts and mention their functions
(a) Production of egg
(b) Site of fertilisation
(c) Site of implantation
(d) Entry of the sperms
Ans.
1. Ovary
2. Oviduct
3. Uterus
4. Vaginal passage
Q.22 What would be the ratio of chromosome number between an egg and its zygote? How is the sperm genetically different from the egg?
Ans. The ratio of chromosome number between an egg and its zygote is 1:2.
Sperm contains the genetic material from the father while the egg contains the genetic material from the mother. Sperm can either have X chromosome or Y chromosome but egg always have an X chromosome.
