Question 3(c)
The number of nuclei present in a zygote is
- none
- one
- two
- four
one
Reason — During fertilisation, the nuclei of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilised egg or zygote.
Key Concepts Covered
This question tests your understanding of the following concepts from the chapter Reproduction in Animals: Question, Number, Nuclei, Present, Zygote, None. These are fundamental topics in Science that students are expected to master as part of the CBSE Class 8 curriculum.
A thorough understanding of these concepts will help you answer similar questions confidently in your CBSE examinations. These topics are frequently tested in both objective and subjective sections of Science papers. We recommend revising the relevant section of your textbook alongside practising these solved examples to build a strong foundation.
How to Approach This Question
Read the question carefully and identify what is being asked. Break down complex questions into smaller parts. Use the terminology and concepts discussed in this chapter. Structure your answer logically — begin with a definition or key statement, then provide supporting details. Review your answer to ensure it addresses all parts of the question completely.
Key Points to Remember
- Read the question carefully and identify all parts before answering.
- Use the terminology specific to this subject and chapter.
- Review the textbook content for this chapter before attempting questions.
- Practice writing concise, well-structured answers within time limits.
Practice more questions from Reproduction in Animals — Science, Class 8 CBSE
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.