Tamil Nadu Class 12 Biology Reproduction in Organisms Notes — Samacheer Kalvi

Quick Summary

Reproduction is the biological process by which organisms produce new individuals. Asexual reproduction is fast and uses one parent; sexual reproduction involves gametes, fertilisation, and genetic variation.

Asexual Reproduction

Main features:

• One parent
• No gamete fusion
• Offspring are usually genetically similar
• Common in simple organisms

Examples:

• Binary fission in Amoeba
• Budding in Hydra
• Fragmentation in some lower organisms
• Regeneration in Planaria

Sexual Reproduction

Main features:

• Formation of male and female gametes
• Fertilisation produces zygote
• Offspring show variation
• Important for evolution

Stages in Sexual Reproduction

1. Pre-fertilisation events 2. Fertilisation 3. Post-fertilisation events

Important Terms

• Juvenile phase
• Reproductive phase
• Senescent phase
• Gametogenesis
• Fertilisation
• Embryogenesis

Asexual vs Sexual Reproduction

Important Questions

One Mark

1. Define reproduction. 2. Name one organism that reproduces by budding. 3. What is fertilisation?

Short Answer

1. Distinguish between asexual and sexual reproduction. 2. Explain the phases in an organism's life cycle. 3. Write short notes on binary fission and budding.

Long Answer

1. Explain the stages in sexual reproduction. 2. Compare asexual and sexual reproduction. 3. Explain why sexual reproduction is important in evolution.

Common Mistakes

• Writing that all offspring from reproduction are identical.
• Confusing fertilisation with gamete formation.
• Forgetting variation when explaining sexual reproduction.
• Listing examples without linking them to the mode of reproduction.

Revision Checklist

• [ ] Asexual reproduction examples
• [ ] Sexual reproduction stages
• [ ] Life-cycle phases
• [ ] Key terms
• [ ] Comparison table