BiologyISC Class 11 · Cell Cycle and Cell Division

The Cell Cycle and Mitosis: Phases, Stages and DNA Content

Updated 17 October 2026 · Fact-checked

The cell cycle has interphase (G1, S, G2) and the M phase (mitosis and cytokinesis). DNA doubles in the S phase (2C to 4C) while the chromosome number is unchanged. Mitosis, with prophase, metaphase, anaphase and telophase, gives two identical daughter cells with the same chromosome number as the parent (equational division).

Understand Cell Cycle Phases and Mitosis

Phases. *Interphase* (the longest part, about 95% of a 24-hour human cell cycle): G1 (cell growth, normal metabolism, preparation for DNA synthesis), S (DNA replication; the amount of DNA doubles from 2C to 4C but the chromosome number stays the same, 2n; centriole duplicates in the cytoplasm), and G2 (protein synthesis and further growth for mitosis). *M phase:* nuclear division (karyokinesis) and cytoplasmic division (cytokinesis). Cells that exit the cycle after G1 and stay metabolically active without dividing are in the quiescent stage G0. In a human cell the cycle takes about 24 hours with about 1 hour for mitosis; in yeast the cycle takes about 90 minutes.

Mitosis (equational division).

*Prophase:* chromatin condenses into chromosomes, each with two chromatids joined at the centromere; the centrosomes move to opposite poles and spindle fibres form; the nucleolus and nuclear envelope disappear.
*Metaphase:* spindle fibres attach to the kinetochores of chromosomes, which align at the equatorial plate (metaphase plate); the best stage to count chromosomes.
*Anaphase:* the centromeres split, and the chromatids (now chromosomes) move to opposite poles, so the number of chromosomes is doubled momentarily.
*Telophase:* chromosomes reach the poles and decondense, the nuclear envelope and nucleolus reappear, forming two daughter nuclei.
*Cytokinesis:* in animal cells a cleavage furrow forms in the plasma membrane and deepens; in plant cells a cell plate forms in the centre (from Golgi vesicles) and grows outward to the wall.

Significance. Growth of the multicellular organism, replacement of damaged and dead cells, repair, and maintenance of the cell's surface area to volume ratio; in plants, meristematic cells divide continuously; it keeps the chromosome number constant. Abnormal control leads to cancer.

Cell Cycle Phases and Mitosis: key facts

Cell cycle: $G 1∣ S ∣ G 2∣ M ∣ G 0$; Interphase = G1 + S + G2.
DNA content: G1 2C
after S and G2 4C
after mitosis 2C each; Chromosome number 2n throughout.
Cell numbers: $C e l l s a f t er n d i v i s i o n s = 2^{n}$; Starting from one cell.
Stages of mitosis: $P r o p ha se ∣ M e t a p ha se ∣ A na p ha se ∣ T e l o p ha se ∣ C y t o k in es i s$; PMAT.

G1	2C
after S and G2	4C
after mitosis	2C each

Cell Cycle Phases and Mitosis in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Healing a cut

Suppose a skin cell in a healing wound completes one cell cycle every 24 hours, and the wound begins with one dividing cell.

Find how many cells arise after 6 days and the percentage of time a cell spends in interphase if mitosis takes 1 hour.

Try it first, then show the solutionSolution

6 days = 6 cell cycles, so cells = 2⁶ = 64.
Interphase = 23 h of 24 h.
Percentage = 23/24 × 100 = 95.8%.

Answer: 64 cells; interphase is about 96% of the cycle.

Memory hook: Mitosis is the shortest part of the cycle.

Tricks to remember Cell Cycle Phases and Mitosis

Short memory aids. Say each one aloud once, then use it on a question the same day.

PMAT
Prophase, Metaphase, Anaphase, Telophase.
Use it when: Order of mitosis.
Anaphase doubles the chromosomes
The chromatids separate, so the chromosome number is 4n momentarily in a 2n cell.
Use it when: Chromosome count questions.

Cell Cycle Phases and Mitosis: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Stage of DNA replication · 1 mark · MCQBoard level

DNA replication in the cell cycle occurs in the:
(a) G1 phase
(b) S phase
(c) G2 phase
(d) M phase

Try it first, then show the solutionSolution

S stands for synthesis: the amount of DNA doubles.

Answer: (b) S phase

Example 2: Stages of mitosis · 3 marks · Short answerBoard level

Describe the events of metaphase and anaphase of mitosis.

Try it first, then show the solutionSolution

Metaphase: chromosomes align at the equatorial plate with kinetochores attached to spindle fibres from both poles. (1.5 marks)
Anaphase: the centromere splits and the sister chromatids move to opposite poles. (1.5 marks)

Answer: Alignment at the equator; chromatids pulled to the poles.

Example 3: DNA content and chromosome number · 4 marks · Short answerHarder board level

A human cell has 46 chromosomes in G1. Give the number of chromosomes and chromatids and the DNA content (C) at G1, G2, anaphase and in each daughter cell.

Try it first, then show the solutionSolution

G1: 46 chromosomes, 46 chromatids, 2C. (1 mark)
G2: 46 chromosomes, 92 chromatids, 4C. (1 mark)
Anaphase: 92 chromosomes (each a single chromatid), 4C in the cell. (1 mark)
Each daughter cell: 46 chromosomes, 2C. (1 mark)

Answer: G1: 46/46/2C; G2: 46/92/4C; anaphase: 92 chromosomes; daughters: 46, 2C.

Example 4: Cytokinesis · 4 marks · Short answerHarder board level

Differentiate cytokinesis in plant and animal cells. Why does a plant cell not use a furrow? Calculate the number of cells formed from one cell after 5 divisions.

Try it first, then show the solutionSolution

Animal cells: a cleavage furrow forms in the plasma membrane and cuts the cell in two. (1 mark)
Plant cells: a cell plate forms from Golgi vesicles at the centre and grows outward to join the cell wall. (1 mark)
A plant cell has a rigid cell wall, so a furrow cannot form. (1 mark)
Number of cells = 2⁵ = 32. (1 mark)

Answer: Furrow (animal) versus cell plate (plant); 32 cells.

Example 5: Cell cycle control · 5 marks · Long answerHOTS / competency

A tissue culture shows that most cells are in G1, a few in S and G2, and very few in M. Explain the observation, name the stage in which cells are arrested if they do not divide again, and give two roles of mitosis. If a cycle takes 20 hours and M phase takes 1 hour, what percentage of cells are expected to be in M phase?

Try it first, then show the solutionSolution

G1 is the longest and the M phase the shortest, so more cells are caught in G1. (1.5 marks)
Cells that leave the cycle after G1 and stay metabolically active are in G0. (1 mark)
Mitosis provides growth and repair (and replacement of lost cells). (1 mark)
Expected fraction in M phase = 1/20 = 5%. (1.5 marks)

Answer: G1 is long; G0 is the quiescent stage; 5% in M phase.

Where students lose marks in Cell Cycle Phases and Mitosis

The slips examiners see most often, and what to write instead.

Mistake: Saying the chromosome number doubles in S phase
Confusing DNA content and chromosome number.
Do this: DNA content doubles; the chromosome number stays 2n.
Usually costs: 2 marks.
Mistake: Placing DNA replication in G2
Wrong phase.
Do this: Replication occurs in S phase.
Usually costs: 1 mark.
Mistake: Wrong cytokinesis for plants
Using a cleavage furrow in plants.
Do this: Plants use a cell plate.
Usually costs: 1 mark.

Exam tips

Draw a graph of DNA content against time for the cell cycle.
Tabulate chromosomes, chromatids and DNA at each stage.
Always say that mitosis is an equational division.
Name the plant and animal cytokinesis differences.

Practice questions on Cell Cycle Phases and Mitosis

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The chromosomes are aligned at the equator in:
(a) prophase
(b) metaphase
(c) anaphase
(d) telophase
Hint
Spindle fibres attach to kinetochores.
Answer
(b) metaphase
Q2 · 2 marks · Short answerBoard level
What happens to the nuclear envelope in prophase and in telophase?
Hint
It disappears and reforms.
Answer
It disintegrates in prophase and reforms around each group of chromosomes in telophase.
Q3 · 3 marks · Short answerHarder board level
Why is mitosis called equational division?
Hint
Think about chromosome number.
Answer
The number of chromosomes in the daughter cells is the same as in the parent cell, so the division is equational; the sister chromatids separate.
Q4 · 3 marks · Short answerHarder board level
A cell of a plant has 2n = 14. Give the number of chromosomes and chromatids in G2, metaphase and anaphase.
Hint
After S phase each chromosome has two chromatids.
Answer
G2 and metaphase: 14 chromosomes, 28 chromatids. Anaphase: 28 chromosomes (as single chromatids move apart).
Q5 · 3 marks · Assertion-reasonHarder board level
Assertion (A): Chromosome number does not change during S phase. Reason (R): DNA replicates but the sister chromatids remain joined at the centromere. Choose: (a) both true and R explains A (b) both true, R does not explain A (c) A true, R false (d) A false, R true.
Hint
Count centromeres.
Answer
(a) Both are true and R explains A.
Q6 · 4 marks · Case-basedHOTS / competency
Case study: Suppose a student looks at an onion root tip squash and counts 200 cells: 180 in interphase, 8 in prophase, 4 in metaphase, 3 in anaphase and 5 in telophase.
(i) Find the mitotic index. (1 mark)
(ii) Name the stage with the fewest cells and give its relative duration. (1 mark)
(iii) State why root tips are used. (1 mark)
(iv) Name the stain commonly used. (1 mark)
Hint
Mitotic index = dividing cells/total cells.
Answer
(i) (8 + 4 + 3 + 5)/200 = 20/200 = 10%. (ii) Anaphase (3 of 200); it is the shortest stage. (iii) They have actively dividing meristematic cells. (iv) Acetocarmine (or aceto-orcein).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Phase of DNA synthesis?Show answer
S.
2.Stage when chromatids separate?Show answer
Anaphase.
3.Quiescent stage?Show answer
G0.
4.DNA in G1?Show answer
2C.

Cell Cycle Phases and Mitosis: frequently asked questions

What is the difference between karyokinesis and cytokinesis?

Karyokinesis is the division of the nucleus; cytokinesis is the division of the cytoplasm.

Why is metaphase the best stage to count chromosomes?

Chromosomes are fully condensed and lie in one plane at the equator.

What is G0?

A resting stage when the cell remains metabolically active but does not divide.