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Cell Cycle and Cell Division – Class 11 Biology notes, important questions and MCQs

NCERT Class 11 Biology, chapter 10. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Cells grow and divide through the cell cycle. Mitosis produces identical cells for growth and repair; meiosis halves the chromosome number for gamete formation.

Cell cycle and mitosis

Interphase (G₁, S – DNA replication, G₂) and M phase; G₀ is a quiescent stage.
Mitosis: prophase, metaphase (chromosomes at equator), anaphase (chromatids separate), telophase; cytokinesis follows.
Plant cells form a cell plate; animal cells form a cleavage furrow.

Meiosis

Meiosis I (reductional) and meiosis II (equational) give four haploid cells.
Prophase I: leptotene, zygotene (synapsis), pachytene (crossing over), diplotene (chiasmata), diakinesis.
Crossing over creates genetic variation; recombinase enzyme is involved.

Key terms

Synapsis: pairing of homologous chromosomes in zygotene
Crossing over: exchange of segments between non-sister chromatids
Kinetochore: disc-shaped structure on the centromere where spindle fibres attach

Important questions with answers

What is the significance of mitosis?2 marks

It keeps the chromosome number the same in daughter cells, allows growth, repair of tissues and replacement of cells, and asexual reproduction in some organisms.

What is the G₀ phase? Give an example.3 marks

A quiescent stage where cells leave the cycle and stop dividing but remain metabolically active; they may re-enter the cycle when needed. Example: heart muscle and nerve cells in adults.

Give the events of anaphase I and anaphase II and explain how meiosis produces genetic variation.5 marks

Anaphase I: homologous chromosomes separate and move to opposite poles, each still made of two sister chromatids (reduction of chromosome number). Anaphase II: centromeres split and sister chromatids separate and move to opposite poles. Variation arises from crossing over in pachytene, which exchanges segments between non-sister chromatids, and from independent assortment of homologous pairs at metaphase I, which mixes maternal and paternal chromosomes in many combinations; random fertilisation adds further variation.

Quick revision

Mitosis = equational.
Crossing over in pachytene.
Meiosis gives 4 haploid cells.

Exam tips

DNA content doubles in S phase, but chromosome number stays the same.
Draw and learn the chromosome number and DNA content (C value) at each stage: G₁ 2C, after S 4C, after meiosis I 2C (n), after meiosis II C (n).

Practice MCQs

DNA replication occurs in
1. G₁ phase
2. G₂ phase
3. S phase
4. M phase
Show answer
Answer: (c) S phase. Synthesis phase.
Mitosis produces
1. 4 haploid cells
2. 2 identical cells
3. 2 haploid cells
4. 4 diploid cells
Show answer
Answer: (b) 2 identical cells. Equational division.
Chromosomes align at the equator in
1. prophase
2. anaphase
3. metaphase
4. telophase
Show answer
Answer: (c) metaphase. Metaphase plate.
Synapsis occurs during
1. leptotene
2. zygotene
3. pachytene
4. diakinesis
Show answer
Answer: (b) zygotene. Pairing of homologues.
The stage in which chromosomes are best studied for counting is
1. prophase
2. anaphase
3. metaphase
4. telophase
Show answer
Answer: (c) metaphase. Most condensed and aligned.
Crossing over takes place in
1. zygotene
2. metaphase I
3. diplotene
4. pachytene
Show answer
Answer: (d) pachytene. Recombination nodules.
A cell with 2n = 20 after meiosis gives cells with
1. 10 chromosomes
2. 20 chromosomes
3. 40 chromosomes
4. 5 chromosomes
Show answer
Answer: (a) 10 chromosomes. Halved.
The longest phase of prophase I is
1. leptotene
2. diplotene
3. pachytene
4. zygotene
Show answer
Answer: (b) diplotene. Can last months or years in oocytes.

All chapters of Class 11 Biology

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.