Chapter 1: Reproduction in Organisms – Long Answer Type Questions

CBSE Class 12 Biology – Long Answer Type Questions with Answers

Unit I: Reproduction | Chapter 1: Reproduction in Organisms (NCERT Based)

Course & Examination Details

• Course: CBSE Class 12 Biology
• Prescribed By: Central Board of Secondary Education
• Syllabus Reference: NCERT
• Unit: Unit I – Reproduction
• Chapter: Chapter 1 – Reproduction in Organisms
• Exam Applicability: CBSE Class 12 Board Examinations (3–5 Mark Questions)

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CBSE Class 12 Biology Chapter 1 Long Answer Questions – Reproduction in Organisms (NCERT)

Section A: Lifespan, Ageing, and Senescence

Q1. Explain the concept of lifespan and factors influencing it in organisms.

Ans:
Lifespan is the duration from birth to natural death of an organism. It is a genetically determined characteristic and varies widely among different species. For example, insects may live for a few days, whereas trees like banyan may survive for hundreds of years. Although genes play a primary role, environmental factors such as nutrition, climate, disease resistance, and availability of resources also influence lifespan. Organisms with efficient repair mechanisms and balanced metabolism tend to live longer. Lifespan is species-specific and remains relatively constant under natural conditions. Understanding lifespan helps explain population dynamics and reproductive strategies adopted by organisms.

Q2. Differentiate between ageing and senescence with suitable examples.

Ans:
Ageing is a gradual and continuous process marked by decline in physiological efficiency of cells, tissues, and organs over time. It begins after maturity and progresses throughout life. Senescence, on the other hand, is the final phase of ageing where deterioration becomes pronounced, leading to loss of reproductive ability and eventual death. For example, in humans, ageing involves gradual weakening of muscles and senses, whereas senescence includes severe organ dysfunction. In plants, ageing may be seen as reduced growth, while senescence may involve leaf fall or death after reproduction, as in annual plants.

Q3. Discuss the biological significance of ageing and senescence.

Ans:
Ageing and senescence play important roles in maintaining ecological balance. Ageing leads to gradual decline in reproductive and physiological efficiency, while senescence removes older and weaker individuals from populations. This allows younger, fitter individuals to access resources, reducing competition. Senescence also ensures turnover in populations, supporting natural selection. In plants, senescence helps in nutrient recycling by transferring nutrients from ageing parts to growing regions. Though ageing ultimately leads to death, it is a natural and essential biological process contributing to population regulation and species survival.

Section B: Types of Reproduction

Q4. Describe reproduction and explain its significance in living organisms.

Ans:
Reproduction is the biological process by which organisms produce new individuals of their own kind. It ensures continuity of species and transfer of genetic information from one generation to the next. Reproduction maintains population size and replaces individuals lost due to death. In sexual reproduction, it introduces genetic variation, which enhances adaptability and evolution. Without reproduction, life would cease to exist after one generation. Thus, reproduction is essential for survival, evolution, and stability of ecosystems.

Q5. Compare asexual and sexual reproduction on the basis of key features.

Ans:
Asexual reproduction involves a single parent and does not require gamete formation or fertilisation. It produces genetically identical offspring called clones and occurs rapidly, as seen in bacteria and Hydra. Sexual reproduction involves two parents or two gametes, includes meiosis and fertilisation, and results in genetic variation. Although slower and energy-intensive, sexual reproduction is evolutionarily advantageous because variation improves adaptability. Thus, asexual reproduction favors rapid multiplication, while sexual reproduction supports long-term survival and evolution.

Section C: Asexual Reproduction

Q6. Explain binary fission and multiple fission with examples.

Ans:
Binary fission is a common asexual reproductive method in unicellular organisms where one parent cell divides into two identical daughter cells. In Amoeba, division occurs in any plane, while in Paramecium it occurs in a definite plane. Multiple fission involves repeated nuclear divisions followed by cytoplasmic division, producing many offspring simultaneously. Plasmodium shows multiple fission during unfavorable conditions. Both methods enable rapid increase in population without the need for gametes or fertilisation.

Q7. Describe budding and fragmentation as modes of asexual reproduction.

Ans:
Budding is a process in which a small outgrowth develops on the parent body, grows, and detaches to form a new individual. It is seen in Hydra and yeast. Fragmentation occurs when the parent organism breaks into fragments, each capable of developing into a complete organism. This method is common in filamentous algae like Spirogyra. Both methods rely on mitotic divisions and result in genetically identical offspring, allowing rapid population growth.

Q8. Explain regeneration and its significance.

Ans:
Regeneration is the ability of an organism to replace lost or damaged body parts. In some organisms like Planaria and starfish, regeneration can result in formation of a complete new individual. It primarily serves repair and maintenance but may also contribute to reproduction. Regeneration is based on the presence of specialized cells capable of dividing and differentiating. It enhances survival by restoring body parts lost due to injury and plays a crucial role in asexual reproduction in simpler organisms.

Section D: Vegetative Propagation in Plants

Q9. Describe vegetative propagation and its types.

Ans:
Vegetative propagation is a form of asexual reproduction in plants using vegetative parts such as roots, stems, or leaves. Natural methods include tubers, rhizomes, bulbs, and runners. Artificial methods include cutting, layering, grafting, and tissue culture. This method produces genetically identical plants and is widely used in agriculture and horticulture to propagate desirable plant varieties efficiently.

Q10. State the advantages and disadvantages of vegetative propagation.

Ans:
Vegetative propagation allows rapid multiplication and preserves desirable traits such as high yield and disease resistance. It is useful for seedless plants and plants with poor seed viability. However, lack of genetic variation makes plants vulnerable to diseases and environmental changes. Since all offspring are clones, a single disease can destroy entire crops propagated vegetatively.

Section E: Sexual Reproduction

Q11. Explain sexual reproduction and its significance.

Ans:
Sexual reproduction involves formation of male and female gametes, their fusion during fertilisation, and development of offspring. It produces genetic variation due to meiosis and recombination. This variation enhances adaptability to changing environments and forms the basis of evolution. Although slower than asexual reproduction, sexual reproduction ensures long-term survival of species by producing diverse and resilient populations.

Q12. Describe the role of meiosis in sexual reproduction.

Ans:
Meiosis is essential in sexual reproduction as it produces haploid gametes from diploid cells. It maintains constant chromosome number across generations and introduces genetic variation through crossing over and independent assortment. These variations result in genetically unique offspring, promoting adaptability and evolution. Without meiosis, sexual reproduction would not maintain genetic balance.

Section F: Events in Sexual Reproduction

Q13. Explain the pre-fertilisation events in sexual reproduction.

Ans:
Pre-fertilisation events include gametogenesis and gamete transfer. Gametogenesis involves formation of male and female gametes by meiosis. Gamete transfer ensures that male and female gametes come together, either through water, wind, insects, or direct contact. These events prepare organisms for fertilisation and successful reproduction.

Q14. Describe fertilisation and its significance.

Ans:
Fertilisation is the fusion of male and female gametes to form a diploid zygote. It restores the diploid chromosome number and initiates embryonic development. Fertilisation may be external or internal. It ensures genetic continuity and variation, making it a crucial step in sexual reproduction.

Q15. Differentiate between external and internal fertilisation.

Ans:
External fertilisation occurs outside the body, usually in aquatic environments, and requires production of large numbers of gametes. Internal fertilisation occurs inside the female body and offers better protection to gametes and developing embryos. Internal fertilisation increases chances of survival but involves fewer gametes.

Section G: Post-Fertilisation Events

Q16. Explain zygote formation and embryogenesis.

Ans:
The zygote is the first diploid cell formed after fertilisation. It undergoes repeated mitotic divisions to form an embryo. Embryogenesis involves cell division, differentiation, and development of organs. It ensures proper growth and formation of a functional organism.

Q17. Distinguish between oviparous and viviparous organisms.

Ans:
Oviparous organisms lay eggs, and development occurs outside the mother’s body, as seen in birds and reptiles. Viviparous organisms give birth to young ones after internal development, as in mammals. Viviparity offers greater protection and nourishment to the embryo.

Section H: Reproductive Health (Basic Concepts)

Q18. Explain reproductive health in organisms.

Ans:
Reproductive health refers to proper functioning of reproductive organs and the ability to produce healthy offspring. It depends on nutrition, environmental conditions, and hormonal balance. Good reproductive health ensures survival and continuity of species.

Q19. Discuss factors affecting reproductive health.

Ans:
Nutrition, environmental conditions, genetic makeup, and physiological balance affect reproductive health. Poor nutrition or unfavorable environment can reduce fertility and offspring survival.

Section I: Conceptual and Application-Based

Q20. Why is asexual reproduction common in unicellular organisms?

Ans:
Unicellular organisms rely on asexual reproduction because it is simple, rapid, and energy-efficient. Their structure does not support complex reproductive systems, making asexual methods suitable.

Q21. Why is sexual reproduction advantageous in changing environments?

Ans:
Sexual reproduction produces genetic variation, enabling populations to adapt to environmental changes and increasing survival chances.

Q22. Explain why clones are less adaptable.

Ans:
Clones lack genetic variation, making them vulnerable to environmental changes and diseases.

Q23. Describe the significance of reproduction in evolution.

Ans:
Reproduction introduces variation and ensures genetic continuity, driving natural selection and evolution.

Q24. Why is fertilisation essential for sexual reproduction?

Ans:
Fertilisation restores diploid chromosome number and initiates development of a new organism.

Q25. Summarise the overall importance of reproduction in living organisms.

Ans:
Reproduction ensures continuity of species, maintains population size, introduces variation, supports evolution, and sustains life on Earth.

CBSE Board Exam Note

These Long Answer Type Questions (120–150 words each) are strictly NCERT-aligned, exam-oriented, and ideal for 4–5 mark questions in CBSE Class 12 Biology board examinations.