Question 9
Differentiate between internal fertilisation and external fertilisation.
| Internal fertilisation | External fertilisation |
|---|---|
| It takes place inside the body of female. | It occurs outside the body. |
| It is observed in human beings and other animals such as hens, cows and dogs. | It is observed in aquatic animals and amphibians such as fish, starfish and frogs. |
| Lesser number of eggs are released. | Many more eggs are released. |
| Survival rate is higher. | Survival rate is low. |
Chapter Overview: Reproduction in Animals
This chapter covers sexual and asexual modes of reproduction in animals. Students learn about human reproductive systems, internal and external fertilisation, embryo development, viviparous and oviparous animals, and asexual methods (budding in Hydra, binary fission in Amoeba). Metamorphosis in frogs and silkworms is an important diagram-based topic.
Board Exam Weightage: 5-7 marks | Difficulty: Moderate to High
Key Formulas & Concepts
| Concept | Details |
|---|---|
| Fertilisation | Sperm + Ovum → Zygote (fusion of male and female gametes) |
| Development Path | Zygote → Embryo → Foetus → Baby |
| Number of Chromosomes | Sperm: 23; Ovum: 23; Zygote: 46 (23 pairs) |
| IVF | In Vitro Fertilisation: fertilisation performed outside the body in a lab dish |
Must-Know Concepts
- Sexual reproduction involves fusion of gametes from two parents; asexual involves one parent
- Internal fertilisation occurs inside the female body (humans, birds); external in water (frog, fish)
- Viviparous animals give birth to live young; oviparous lay eggs
- Hens use internal fertilisation but are oviparous (lay eggs)
- Budding: outgrowth from parent body (Hydra); Binary fission: parent splits into two halves (Amoeba)
- Metamorphosis: drastic change in form from larva to adult (frog tadpole, silkworm caterpillar)
Sexual vs Asexual Reproduction
| Feature | Sexual | Asexual |
|---|---|---|
| Parents | Two (male and female) | One |
| Gametes | Involved (sperm + ovum) | Not involved |
| Genetic Variation | Present (offspring differ from parents) | Absent (offspring identical to parent) |
| Examples | Humans, dogs, fish, birds | Hydra (budding), Amoeba (fission) |
Common Mistakes to Avoid
- Confusing internal and external fertilisation
- Thinking oviparous means external fertilisation (hens are oviparous but use internal fertilisation)
- Confusing embryo (early stage) and foetus (has recognisable body parts)
- Thinking budding and binary fission are the same process
Scoring Tips
- Draw and label reproductive systems with clear labels
- Learn the development sequence: zygote → embryo → foetus → baby
- Make a viviparous/oviparous classification chart with 10 animals
- Draw life cycles of frog and silkworm for metamorphosis questions
Frequently Asked Questions
Q: How many marks does this chapter carry in the exam?
A: Approximately 5-7 marks in the annual exam.
Q: What question types are commonly asked?
A: MCQs (1 mark), Very Short Answer (2 marks), Short Answer (3 marks), and Long Answer / Diagram (5 marks).
Q: Is this chapter important for competitive exams?
A: Yes, concepts from this chapter appear in NTSE, Olympiad, and other science competitions.