Chapter 1: Reproduction in Organisms Class 12 Biology NCERT Solutions

NCERT Solutions for Class 12 Biology Chapter 1 – Reproduction in Organisms

Question 1. Why is reproduction essential for organisms?

Reproduction is vital because it allows living organisms to produce new individuals of their own kind. This biological process ensures the continuity of a species across generations. Additionally, reproduction introduces variations in the population, which are important for adaptation and evolutionary processes.

Question 2. Which is a better mode of reproduction: sexual or asexual? Why?

Sexual reproduction is considered better due to the following reasons:

• Genetic Variation: Fusion of gametes from two different parents results in genetic recombination, introducing variations.
• Evolutionary Advantage: Variations support natural selection and drive evolution.
• Better Adaptability: Offspring produced through sexual reproduction are better equipped to survive environmental changes.
• Increased Vigor: Sexual reproduction enhances the vitality of the offspring due to diverse genetic backgrounds.

Question 3. Why is the offspring formed by asexual reproduction referred to as a clone?

In asexual reproduction, a single parent produces offspring without the fusion of gametes. These offspring are genetically and physically identical to the parent and to one another. Hence, they are termed clones.

Question 4. Offsprings formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?

Offspring from sexual reproduction generally have better survival prospects because they inherit a mix of genetic traits from both parents, leading to variability. This diversity improves adaptability and resistance to diseases. However, this may not always be true in every scenario, as survival also depends on environmental factors and individual fitness.

Question 5. How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?

Asexual reproduction: Involves only one parent and produces offspring that are genetically identical (clones) through mitotic cell division.

Sexual reproduction: Requires two parents and involves gamete fusion, resulting in offspring with genetic diversity due to meiotic division and recombination.

Question 6. Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered a type of asexual reproduction?

Differences:

• Asexual reproduction involves one parent; sexual reproduction involves two.
• No gametes or fertilization in asexual; gamete fusion is essential in sexual reproduction.
• Asexual results in clones; sexual produces genetically varied individuals.

Vegetative reproduction is a form of asexual reproduction as it involves the development of new plants from vegetative parts (like tubers, runners, etc.) without gamete involvement.

Question 7. What is vegetative propagation? Give two suitable examples.

Vegetative propagation is the process by which new plants grow from parts like tubers, bulbs, rhizomes, and suckers. These parts, called vegetative propagules, develop into complete plants.

Examples:

• New shoots from potato tubers (eyes)
• Growth from the rhizomes of ginger and banana

Question 8. Define:

• (a) Juvenile phase: The early phase of life before sexual maturity. In plants, it is termed the vegetative phase.
• (b) Reproductive phase: The phase when an organism becomes sexually mature and capable of reproduction.
• (c) Senescent phase: The final stage of the life span where aging and decline occur, leading eventually to death.

Question 9. Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?

Sexual reproduction, despite being complex and energy-intensive, offers the benefits of genetic variation, increased adaptability, and evolutionary advancement. These advantages help higher organisms survive in changing environments.

Question 10. Explain why meiosis and gametogenesis are always interlinked.

Gametogenesis is the formation of haploid gametes. Meiosis is crucial in this process as it reduces the chromosome number by half, ensuring the gametes are haploid. Hence, meiosis and gametogenesis are interdependent processes.

Question 11. Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).

• Ovary – 2n
• Anther – 2n
• Egg – n
• Pollen – n
• Male gamete – n
• Zygote – 2n

Question 12. Define external fertilization. Mention its disadvantages.

External fertilization is the fusion of gametes outside the body, often in an aquatic medium (e.g., in fishes, amphibians).

Disadvantages:

• Limited to aquatic environments
• High risk of gamete loss or damage due to water currents
• Offspring receive no parental protection, increasing mortality risk

Question 13. Differentiate between a zoospore and a zygote.

• Zoospore: A haploid, flagellated, motile spore formed during asexual reproduction.
• Zygote: A diploid, non-flagellated cell formed by fusion of two gametes during sexual reproduction.

Question 14. Differentiate between gametogenesis and embryogenesis.

• Gametogenesis: Formation of gametes (sperm and egg) through meiosis.
• Embryogenesis: Development of an embryo from the zygote after fertilization.

Question 15. Describe the post-fertilization changes in a flower.

After fertilization:

• Petals, sepals, and stamens usually fall off.
• The ovary enlarges and transforms into a fruit.
• Ovules develop into seeds.
• The zygote develops into an embryo.
• The pericarp (fruit wall) forms to protect the developing seeds.

Question 16. 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.

A bisexual flower contains both male (stamens) and female (carpels) reproductive parts.

Examples:

• Mustard – Brassica campestris
• Onion – Allium cepa
• Pea – Pisum sativum
• Petunia – Petunia hybrida
• Hibiscus – Hibiscus rosa-sinensis

Question 17. 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?

In cucurbits:

• Staminate flowers have stamens (male part) and do not bear fruit.
• Pistillate flowers have carpels (female part) and develop into fruits after fertilization.

Other examples of plants with unisexual flowers: Papaya, Mulberry, Date Palm.

Question 18. Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?

Oviparous animals lay eggs that develop outside the mother’s body. These eggs are exposed to environmental threats and predators.

In contrast, viviparous animals give birth to live young, providing protection and nourishment during development, resulting in better chances of survival.