Q1. Why is reproduction essential for organisms?
Solution:- An organism gives rise to young ones by reproduction. The offspring grow, mature, and in turn, produce new offspring. Thus, there is a cycle of birth, growth, and death. Reproduction enables the continuity of the species, generation after generation. So, therefore reproduction is essential.
Q2. Which Is a better mode of reproduction: sexual or asexual? Why?
Solution:- Sexual reproduction is a better mode of reproduction than asexual mode because the former contributes to the evolution of the species by introducing variation in a population and occurs much more rapidly. Variation in a population occurs because of the fusion of male and female gametes (sexual reproduction) carrying different sets of chromosomes.
Q3. Why is the offspring formed by asexual reproduction referred to as clones?
Solution:- In sexual reproduction, the offspring is morphologically and genetically identical to the parent and to each other. Hence, it is called a clone.
Q4. Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
Solution:- The offspring that are produced by sexual reproduction are not genetically identical to their parents. They exhibit variations because they receive chromosomes from two different parents. Since they show variation, they are highly adapted to the changing environment. Asexually produced organisms are genetically identical and all organism show similar adaptations. So, during any calamity, there is a possibility that the whole generation would destroy leading to extinction of species. However, this statement is not true always because of some inborn genetic disorder due to which organism have a risk in their survival, e.g., Haemophilia.
Q5. How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Solution:- The progenies have similar genetic make-up and are exact copies of their parents in asexual reproduction but the progenies have different genetic make-up and different from each other and dissimilar to the parent in sexual reproduction.
Variation is absent in asexual reproduction but it is a common phenomenon of sexual reproduction. In asexual reproduction, variation may occur due to mutation whereas variation occurs due to mutation, crossing over, and recombination in sexual reproduction.
Q6. Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
Solution:- The differences between asexual and sexual reproduction are given in the following table:
| Asexual reproduction | Sexual reproduction |
|---|---|
| It does not involve the fusion of male and female gametes. | There is fusion of gametes therefore progeny are not identical to parents. |
| Single parent involved | Two parents involved usually. |
| The offspring are identical to the parent and are called clones. | The offspring are not identical to their parents and show variations from each other and their parents. |
| It does not play important role in the evolution process. | It play important role in the evolution process. |
| It is common in single-celled organisms or organisms with simple structures. | It is common in high-level organisms which have a complex structure. |
| Only mitotic cell division takes place. | It involves both meiosis and mitosis. |
| The rate of reproduction is faster | The rate of reproduction is slower |
Q7. What is vegetative propagation? Give two suitable examples.
Answer:- Vegetative propagation is the process of reproducing plants from any portion of the vegetative organs of the plant without involving the seeds or spores. It involves only single parents and considered asexual reproduction. Examples of vegetative propagation are:
• Eyes (buds) on the potato tuber.
• Adventitious buds on the leaves of Bryophyllum are capable of giving rise to new plants
Q8. Define
(a) Juvenile phase,
(b) Reproductive phase,
(c) Senescent phase
Answer:-
(a) The period of growth from birth up to a stage, where the organism will start undergoing changes leading to reproductive maturity is known as Juvenile phase.
(b) The period during which an organism is sexually mature and can produce gametes that can give rise to new organisms is known as Reproductive phase.
(c) The period from the end of the reproductive phase till death. In this period, slower metabolism, break down of proteins, immobilisation of nutrients takes place in animals whereas in plants, leaves become yellow and fall off.
Q9. Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
Answer:- Higher organisms have resorted to sexual reproduction because it allows genetic variations through the combination of different genetics in gametes and improves the genetic makeup in the offspring. These factors may give survival advantages to species and contribute to evolution.
Q10. Explain why meiosis and gametogenesis are always interlinked?
Answer:- Haploid gametes can be produced only through meiosis and gametogenesis is the process of formation of gametes. The gametes produced by gametogenesis are always haploid, while the body of an organism is diploid. Therefore, it is necessary that meiosis has to occur for the formation of haploid gametes which ensures half number of chromosomes in the developing gametes.
Q11. Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).
(a) Ovary _______
(b) Anther ______
(c) Egg _________
(d) Pollen _______
(e) Male gamete __
(f) Zygote _______
Answer:-
(a) Ovary Diploid
(b) Anther Diploid
(c) Egg Haploid
(d) Pollen Haploid
(e) Male gamete Haploid
(f) Zygote Diploid
Q12. Define external fertilization. Mention its disadvantages.
Answer:- External fertilisation is a type of fertilization that occurs outside the female body, in external medium, such as water.
Disadvantages of external fertilixation are
• Very less chance of fusion of male and female gametes.
• Offspring are vulnerable to predators because of no parental care.
Q13. Differentiate between a zoospore and a zygote.
Answer:-
| Zoospore | Zygote |
|---|---|
| It is an asexual reproductive structure. | It is sexual reproductive structure. |
| It is a motile asexual spore that uses flagella for movement. | It is a non-motile cell. |
| It can be haploid or diploid. | It is diploid |
| It germinates to directly give rise to new plants. | It develops into an embryo that further differentiates to form a new individual. |
Q14. Differentiate between gametogenesis from embryogenesis.
Answer:-
| Gametogenesis | Embryogenesis |
|---|---|
| It is the process of the generation of haploid gametes. | It is the process of formation of embryo. |
| It involves meiosis. | It involves mitosis. |
| Further transformation may be required to make male gametes motile | Further cell differentiation required for the formation of specialized tissues and organs. |
Q15. Describe the post-fertilization changes in a flower.
Answer:- Post-fertilization changes in flower are:
• The sepal, petal and stamen of the flower withers and fall off only pistil remains attached to the plant.
• The zygote develops into the embryo.
• The ovules develop into the seed.
• The ovary develops into the fruit.
• The ovary wall is transformed into a protective layer called the pericarp which covers the fruit.
Q16. What is a bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
Answer:- A flower bearing both male and female organs (stamens and pistil) is called a bisexual flower.Flowers with common name and scientific names:
• Rose – Rosa alba
• Water lily – Nymphaea odorata• Sun flower – Helianthus annus
• China rose – Hibiscus Rosa-sinensis
• Mustard – Brassica nigra
Q17. Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers?
Answer:- Cucurbit plant bears separate male and female flowers. The staminate flowers bear bright, yellow coloured petals along with stamens representing the male reproductive structure while the pistillate flowers bear only the pistil representing the female reproductive structure.
Q18. Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Answer:- The offsprings of oviparous animals are at a greater risk because they develop outside the female body and are exposed to various environmental conditions and predator threat whereas in viviparous animals, young ones develop inside the female body, which ensures proper embryonic care and protection.
NCERT Solutions for Class 12 Biology
- Chapter 1 Reproduction in Organisms
- Chapter 2 Sexual Reproduction in Flowering Plants
- Chapter 3 Human Reproduction
- Chapter 4 Reproductive Health
- Chapter 5 Principles of Inheritance and Variation
- Chapter 6 Molecular Basis of Inheritance
- Chapter 7 Evolution
- Chapter 8 Human Health and Disease
- Chapter 9 Strategies for Enhancement in Food Production
- Chapter 10 Microbes in Human Welfare
- Chapter 11 Biotechnology: Principles And Processes
- Chapter 12 Biotechnology and its Applications
- Chapter 13 Organisms and Populations
- Chapter 14 Ecosystem
- Chapter 15 Biodiversity and Conservation
- Chapter 16 Environmental Issues