Cell Division: Q & A

O Level Biology Questions and Answers

Subject: Biology

Level: O Level

Topic: Cell Division

This resource provides a complete set of O Level Biology Questions and Answers on cell division – the process by which cells replicate to produce new cells for growth, repair, and reproduction. You will explore the stages of mitosis and meiosis, their differences, and their biological significance. Perfect for mastering these essential topics.

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Topic Overview

Cell division is essential for growth, repair, and reproduction. Mitosis produces two identical diploid daughter cells for growth and tissue repair. Meiosis produces four genetically diverse haploid gametes for sexual reproduction. Mitosis involves one division, while meiosis involves two divisions (meiosis I and II). Key stages include prophase, metaphase, anaphase, and telophase. Understanding these processes is fundamental to genetics, development, and evolution.

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Exam Questions and Answers

Question 1

Question:
State two differences between mitosis and meiosis.

Answer:
1. Mitosis produces two daughter cells; meiosis produces four.
2. Daughter cells from mitosis are genetically identical; those from meiosis are genetically different.

Explanation:
Mitosis is for growth and repair, preserving genetic identity. Meiosis is for gamete formation, introducing genetic variation through crossing over and independent assortment.

Exam Tip:
Use comparative language. You can also mention chromosome number: mitosis maintains diploid number; meiosis halves it.

Question 2

Question:
Describe the role of mitosis in living organisms.

Answer:
Mitosis is responsible for growth (increase in cell number), repair of damaged tissues, and asexual reproduction in some organisms. It ensures that new cells are genetically identical to the parent cell.

Explanation:
During growth, mitosis produces new cells. After injury, it replaces lost cells. In asexual reproduction, it creates offspring identical to the parent.

Exam Tip:
Give specific examples: “skin cells replace damaged ones”, “bacteria divide by binary fission (similar to mitosis)”, or “plants grow from meristems by mitosis”.

Question 3

Question:
Explain the importance of meiosis in sexual reproduction.

Answer:
Meiosis produces haploid gametes (sperm and eggs) so that when they fuse during fertilization, the diploid chromosome number is restored. It also introduces genetic variation through crossing over and independent assortment, increasing diversity.

Explanation:
Without meiosis, chromosome number would double each generation. Genetic variation is crucial for adaptation and survival.

Exam Tip:
Use the terms “haploid”, “diploid”, “genetic variation”, and “fertilization”. Mention crossing over and independent assortment for higher marks.

Question 4

Question:
List the four stages of mitosis in order and describe what happens in metaphase.

Answer:
Order: Prophase, Metaphase, Anaphase, Telophase. In metaphase, chromosomes line up at the equator (centre) of the cell, and spindle fibres attach to their centromeres.

Explanation:
Proper alignment ensures that when chromosomes are pulled apart in anaphase, each daughter cell receives an identical set.

Exam Tip:
Learn the mnemonic “PMAT” (Prophase, Metaphase, Anaphase, Telophase). Be able to describe what happens in each stage.

Question 5

Question:
What is crossing over and during which phase of meiosis does it occur?

Answer:
Crossing over is the exchange of genetic material between non‑sister chromatids of homologous chromosomes. It occurs during prophase I of meiosis.

Explanation:
Crossing over creates new combinations of alleles on chromosomes, contributing to genetic variation in gametes.

Exam Tip:
Be specific: “prophase I”. Mention that it involves homologous chromosomes and results in recombinant chromosomes.

Question 6

Question:
Explain why daughter cells produced by mitosis are genetically identical, but those from meiosis are not.

Answer:
Mitosis involves one division where chromosomes replicate and are equally distributed, giving identical sets. Meiosis involves two divisions; during prophase I, crossing over shuffles alleles, and during metaphase I, independent assortment randomly distributes maternal and paternal chromosomes, leading to varied combinations.

Explanation:
These processes ensure genetic diversity, which is beneficial for populations facing environmental changes.

Exam Tip:
Mention both crossing over and independent assortment. Use diagrams if possible in your revision.

Question 7

Question:
Compare the chromosome number of cells produced by mitosis and meiosis in humans.

Answer:
In humans, mitosis produces diploid cells with 46 chromosomes (23 pairs). Meiosis produces haploid gametes with 23 chromosomes (single set).

Explanation:
Fertilization restores the diploid number (23 + 23 = 46). The reduction is essential to prevent doubling each generation.

Exam Tip:
Always use the correct human chromosome numbers. Generalise: “mitosis keeps the same number; meiosis halves it”.

Question 8

Question:
Describe how the structure of a chromosome changes during mitosis.

Answer:
Before mitosis, DNA replicates, and chromosomes become visible as two identical sister chromatids joined at a centromere. During prophase, they condense further. In anaphase, the sister chromatids separate and move to opposite poles. In telophase, they decondense to form chromatin again.

Explanation:
These changes ensure accurate segregation of genetic material. Chromatin condensation allows easier movement during division.

Exam Tip:
Use terms “chromatin”, “sister chromatids”, “centromere”. Connect structure to function: condensation prevents tangling and aids separation.

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Key Concepts Summary

• Mitosis: one division → two identical diploid cells; used for growth, repair, asexual reproduction.
• Meiosis: two divisions → four non‑identical haploid gametes; used for sexual reproduction.
• Stages of mitosis: Prophase, Metaphase, Anaphase, Telophase (PMAT).
• Meiosis includes crossing over (prophase I) and independent assortment (metaphase I) → genetic variation.
• Chromosome number: mitosis preserves; meiosis halves.

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Frequently Asked Questions

What is the difference between chromatin and chromosomes?

Chromatin is the uncoiled, thread‑like form of DNA present during interphase. Chromosomes are the condensed, visible structures formed when DNA coils around proteins during cell division.

Why is meiosis called “reduction division”?

Meiosis reduces the chromosome number from diploid (2n) to haploid (n). This is essential so that when gametes fuse, the offspring has the correct diploid number.

Does mitosis occur in all cells?

Mitosis occurs in somatic (body) cells. Some specialized cells (e.g., neurons, muscle cells) lose the ability to divide after differentiation and do not undergo mitosis.

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Conclusion

Mastering O Level Biology Questions and Answers on cell division gives you a strong foundation in how organisms grow, repair, and reproduce. Understand the stages of mitosis and meiosis, their differences, and the role of genetic variation. Practice these questions, review the key concepts, and use the exam tips to perform well in your exams.