Class 12 Biology Chapter 1 Reproduction in Organisms Notes
1. Importance of Reproduction
Reproduction is a fundamental characteristic of all living organisms. It is the biological process by which organisms produce new individuals similar to themselves.
Importance:
Ensures continuity of a species from one generation to the next
Introduces variations, which are essential for:
Adaptation
Evolution
Helps organisms survive under changing environmental conditions
Thus, reproduction is essential for the survival and evolution of life on Earth.
2. Sexual Reproduction as a Better Mode of Reproduction
Sexual reproduction is considered a better mode of reproduction as compared to asexual reproduction.
Reasons:
Variation: Fusion of gametes from two parents leads to genetic recombination
Evolution: Variations play a key role in natural selection
Adaptation: Offspring adapt better to environmental changes
Vigour and vitality: Genetic recombination improves survival ability
3. Asexual Reproduction and Clones
In asexual reproduction, a single parent produces offspring without gamete formation.
Why offspring are called clones:
Offspring are genetically identical to the parent
They are also morphologically similar
Such identical individuals are called clones
4. Survival Advantage of Sexual Reproduction
Offspring produced by sexual reproduction generally have better chances of survival.
Reason:
Genetic material comes from both parents
Leads to variation, which helps in:
Adaptation
Evolution
Survival in changing conditions
This statement is true, as sexual reproduction provides vigour and adaptability.
5. Difference Between Asexual and Sexual Reproduction (Concept)
Asexual Reproduction:
Single parent involved
No formation or fusion of gametes
Only mitotic division
Offspring genetically identical
Sexual Reproduction:
Two parents involved
Formation and fusion of gametes
Involves meiosis
Offspring genetically different
6. Asexual vs Sexual Reproduction & Vegetative Reproduction
Key Differences:
Asexual reproduction involves one parent and no gametes
Sexual reproduction involves two parents and gametes
Vegetative reproduction:
Considered a type of asexual reproduction
New plants arise from vegetative parts like:
Rhizome
Tuber
Bulb
Runner
No involvement of two parents
7. Vegetative Propagation
Vegetative propagation is the formation of new plants from vegetative parts instead of seeds.
Vegetative propagules:
Runner
Rhizome
Tuber
Bulb
Offset
Examples:
Potato (eyes of tuber)
Banana (rhizome)
Ginger
Sweet potato
Dahlia
8. Phases of Life Cycle
(a) Juvenile Phase:
Period before sexual maturity
Known as vegetative phase in plants
Duration varies among organisms
(b) Reproductive Phase:
Begins after juvenile phase
Organisms produce offspring
Marked by flowering in plants
In animals, shows physiological changes
(c) Senescent Phase:
Last phase of life
Characterised by ageing
Metabolism slows down
Ends in death
9. Preference of Sexual Reproduction in Higher Organisms
Despite being complex, higher organisms prefer sexual reproduction because:
Produces more variation
Supports faster evolution
Helps survival in unfavourable conditions
Ensures continuity of species
10. Link Between Meiosis and Gametogenesis
Gametogenesis forms haploid gametes
Meiosis reduces chromosome number from diploid to haploid
Therefore, gametogenesis is always linked with meiosis
11. Haploid and Diploid Parts of a Flowering Plant
| Part | Chromosome Number |
|---|---|
| Ovary | 2n |
| Anther | 2n |
| Egg | n |
| Pollen | n |
| Male gamete | n |
| Zygote | 2n |
12. External Fertilization
External fertilization occurs when fusion of gametes takes place outside the body.
Features:
Requires water as medium
Seen in fishes, amphibians, algae
Disadvantages:
Restricted to aquatic environment
Depends on chance and synchrony
No protection to offspring
High risk from predators
13. Zoospore vs Zygote
Zoospore:
Formed during asexual reproduction
Motile and flagellated
Haploid or diploid
Zygote:
Formed by fusion of gametes
Always diploid
Product of sexual reproduction
14. Gametogenesis vs Embryogenesis
Gametogenesis:
Formation of gametes
Involves meiosis
Embryogenesis:
Development of embryo from zygote
Involves mitotic divisions
15. Post-Fertilization Changes in Flower
After fertilization:
Sepals, petals and stamens fall off
Zygote develops into embryo
Ovule becomes seed
Ovary develops into fruit
Ovary wall forms pericarp
Seeds germinate under favourable conditions
16. Bisexual Flowers
Bisexual flowers have both male and female reproductive organs.
Examples:
Mustard – Brassica campestris
Onion – Allium cepa
Pea – Pisum sativum
Petunia – Petunia hybrida
China rose – Hibiscus rosa-sinensis
17. Unisexual Flowers in Cucurbits
Staminate (male) flowers:
Bright petals
Prominent stamens
Do not form fruits
Pistillate (female) flowers:
Ovary present
Develop into fruits after fertilization
Other unisexual plants:
Papaya
Mulberry
Date palm
18. Risk in Oviparous Animals
Oviparous animals:
Lay eggs
Less protection to embryo
Viviparous animals:
Embryo develops inside female body
Better nourishment and protection
Hence, offspring of oviparous animals are at greater risk.
Top 10 Short Question–Answers
Q1. What is reproduction?
Answer: Reproduction is the biological process by which organisms produce new individuals similar to themselves.
Q2. Why is reproduction important for living organisms?
Answer: It ensures continuity of species, introduces variations, and supports adaptation and evolution.
Q3. Why is sexual reproduction considered better than asexual reproduction?
Answer: Because it produces variation through genetic recombination, which helps in evolution and survival.
Q4. What are clones?
Answer: Offspring produced by asexual reproduction that are genetically and morphologically identical to the parent are called clones.
Q5. How does sexual reproduction provide survival advantage?
Answer: It produces variation by combining genetic material from two parents, improving adaptability.
Q6. Name the type of reproduction in which only one parent is involved.
Answer: Asexual reproduction.
Q7. What is vegetative propagation?
Answer: It is the formation of new plants from vegetative parts instead of seeds.
Q8. Name any two vegetative propagules.
Answer: Rhizome and tuber.
Q9. What is the juvenile phase?
Answer: It is the period before sexual maturity; called vegetative phase in plants.
Q10. Why is gametogenesis linked with meiosis?
Answer: Because meiosis reduces chromosome number to form haploid gametes.
Long Answer Questions
Q1. Explain the importance of reproduction in living organisms.
Answer:
Reproduction is essential for life due to the following reasons:
Continuity of species: It ensures survival of a species from one generation to the next
Variation: Introduces genetic differences among offspring
Adaptation: Helps organisms adjust to changing environments
Evolution: Variations are the basis of natural selection
Thus, reproduction is vital for survival and evolution of life on Earth.
Q2. Describe the differences between asexual and sexual reproduction.
Answer:
Asexual Reproduction:
Involves only one parent
No formation or fusion of gametes
Only mitotic division occurs
Offspring are genetically identical (clones)
Sexual Reproduction:
Involves two parents
Formation and fusion of gametes
Meiosis occurs
Offspring are genetically different
Q3. Explain vegetative propagation with examples.
Answer:
Vegetative propagation is a type of asexual reproduction in which new plants develop from vegetative parts.
Vegetative propagules include:
Runner
Rhizome
Tuber
Bulb
Offset
Examples:
Potato – eyes of tuber
Banana – rhizome
Ginger
Sweet potato
Dahlia
📝 PYQs (Previous Year Questions)
🔹 1️⃣ Very Short Answer Questions (1 Mark)
What is reproduction?
Why are asexual offspring called clones?
Name the type of reproduction that involves only one parent.
Which cell division is involved in asexual reproduction?
Name any one vegetative propagule.
What is the chromosome number of a zygote?
Which phase of life cycle shows ageing?
What is the chromosome number of pollen grain?
Name the phase of life cycle when an organism becomes sexually mature.
What type of fertilization occurs in fishes?
🔹 2️⃣ Short Answer Questions (2–3 Marks)
State any two importance of reproduction.
Why is sexual reproduction considered better than asexual reproduction?
Differentiate between asexual and sexual reproduction (any two points).
What is vegetative propagation? Give two examples.
What is external fertilization? Mention any two disadvantages.
Write two differences between zoospore and zygote.
What is juvenile phase? What is it called in plants?
Why is gametogenesis always associated with meiosis?
🔹 3️⃣ Long Answer Questions (3–5 Marks)
Explain the significance of sexual reproduction in higher organisms.
Describe the phases of life cycle in organisms.
Differentiate between asexual and sexual reproduction.
Explain vegetative propagation with suitable examples.
Describe post-fertilization changes in a flowering plant.
Why are offspring of oviparous animals at greater risk than viviparous animals?
🔹 4️⃣ Assertion–Reason / Concept-Based PYQs
Sexual reproduction provides better survival advantage. Justify.
Higher organisms prefer sexual reproduction despite its complexity. Explain.
External fertilization is considered risky. Give reasons.
🔹 5️⃣ Diagram / Table-Based PYQs (Asked indirectly)
Write haploid and diploid parts of a flowering plant.
Distinguish between gametogenesis and embryogenesis.
❓ 4️⃣ FAQs (5)
FAQ 1. Why are variations important in reproduction?
Variations help organisms adapt, survive environmental changes, and drive evolution.
FAQ 2. Why are asexual offspring called clones?
Because they are genetically identical to the parent and to each other.
FAQ 3. Why do higher organisms prefer sexual reproduction?
It produces more variation, supports faster evolution, and ensures better survival.
FAQ 4. What happens after fertilization in flowering plants?
Zygote forms embryo, ovule becomes seed, ovary becomes fruit, and ovary wall forms pericarp.
FAQ 5. Why are oviparous animals at greater risk?
Their embryos develop outside the body with less protection and nourishment.
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