Cell Cycle and Cell Division NCERT Line by Line for NEET 2026 – Complete Detailed Notes with Diagrams

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Cell Cycle and Cell Division

NCERT Line-by-Line Breakdown for NEET 2026

Unit 3: Cell Structure & Function

Growth and reproduction are characteristics of cells. All cells reproduce by dividing into two. The sequence of events by which a cell duplicates its genome, synthesizes other constituents, and eventually divides into two daughter cells is termed the Cell Cycle.

1. The Cell Cycle

A typical human cell divides once every 24 hours (Yeast takes only 90 minutes). The cycle is divided into two basic phases:

⏳ Interphase (Resting Phase)

Lasts for more than 95% of the duration. Divided into:

  • G1 Phase (Gap 1): Cell is metabolically active and grows continuously. No DNA replication.
  • S Phase (Synthesis): DNA replication takes place. DNA content doubles (2C → 4C) but Chromosome number remains same (2n). Centriole duplicates in cytoplasm.
  • G2 Phase (Gap 2): Proteins are synthesized in preparation for mitosis.

⚔️ M Phase (Mitosis)

The actual cell division. Starts with nuclear division (Karyokinesis) and ends with Cytokinesis.

G0 Phase (Quiescent Stage): Cells that do not divide further (e.g., Heart cells) exit G1 and enter an inactive stage called G0. They remain metabolically active but do not proliferate.

2. Mitosis (Equational Division)

Occurs in somatic cells. Chromosome number remains the same in daughter cells.

StageKey Events (NEET Keywords)
ProphaseChromosomal material condenses. Centrosomes move to opposite poles. Nuclear envelope, Golgi, ER disappear.
MetaphaseChromosomes align at the Metaphase plate. Spindle fibers attach to Kinetochores.
(Best stage to study morphology of chromosomes).
AnaphaseCentromeres split. Chromatids move to opposite poles.
(Best stage to study shape of chromosomes – V, L, J, I).
TelophaseChromosomes decondense. Nuclear envelope reappears. (Reverse of Prophase).
✂️ Cytokinesis (Division of Cytoplasm)
• Animal Cells: Furrow formation (Centripetal).
• Plant Cells: Cell plate formation (Centrifugal). Precursor is Middle Lamella.

3. Meiosis (Reductional Division)

Occurs in gamete formation. Reduces chromosome number by half (2n → n). Involves two cycles: Meiosis I and Meiosis II.

Meiosis I: Prophase I (The Longest Phase)

This is the most asked topic in NEET. Remember the mnemonic: Little Zara Plays Daily Dance.

1. Leptotene
Chromosomes become visible (Bouquet stage).
2. Zygotene
Pairing of homologous chromosomes (Synapsis). Formation of Synaptonemal Complex. Pairs called Bivalents.
3. Pachytene
Crossing Over occurs. Exchange of genetic material. Enzyme: Recombinase.
4. Diplotene
Dissolution of synaptonemal complex. X-shaped structures visible called Chiasmata. (Can last years in oocytes).
5. Diakinesis
Terminalisation of chiasmata. Nucleolus disappears.

Rest of Meiosis

  • Metaphase I: Bivalents align (Double metaphase plate).
  • Anaphase I: Homologous chromosomes separate (Segregation). Centromere does NOT split.
  • Meiosis II: Similar to Mitosis. Centromere splits in Anaphase II.

📝 Rapid Fire MCQs

Q1. In which phase of the cell cycle does the amount of DNA per cell double?

  • A) G1 phase
  • B) G2 phase
  • C) S phase
  • D) M phase
Click to check Answer

Answer: C) S phase (DNA synthesis).

Q2. The enzyme recombinase is required at which stage of meiosis?

  • A) Pachytene
  • B) Zygotene
  • C) Diplotene
  • D) Diakinesis
Click to check Answer

Answer: A) Pachytene (Crossing over).

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