NEET Biology — Chapter 10

Cell Cycle and Cell Division

Cell Cycle and Cell Division covers the phases of the cell cycle (G₁, S, G₂, M), the events of mitosis (with each phase), and meiosis — with particular focus on Prophase I substages and the significance of crossing over. NEET sets 2–4 MCQs from this chapter every year. The five substages of Prophase I, the mitosis vs meiosis comparison table, and the timing of crossing over are the highest-yield topics.

12345

1. Cell Cycle — Phases and Duration

The cell cycle is the sequence of events from one cell division to the next. It has two major stages:

  • Interphase (~90–95% of cycle time) — cell grows and prepares for division:
    — G₁ phase (first growth phase): cell grows; proteins synthesised; organelles increase.
    — S phase (synthesis phase): DNA replication; each chromosome becomes a pair of sister chromatids.
    — G₂ phase (second growth phase): cell continues to grow; prepares for mitosis.
    — G₀ phase: quiescent; cells that have left the cycle (e.g., neurons, muscle cells).
  • M phase (Mitotic phase) — cell division: karyokinesis (nuclear division) + cytokinesis (cytoplasmic division).
NEET tip: DNA replication occurs only once per cell cycle, during S phase. G₁ and G₂ are checkpoints where the cell decides whether to proceed or not. Cyclins and CDKs (cyclin-dependent kinases) control progression through checkpoints.

2. Mitosis — Phases and Events

Mitosis produces two daughter cells genetically identical to the parent. It is the basis of growth, repair, and asexual reproduction. Mitosis has four stages plus cytokinesis:

PhaseKey events
ProphaseChromatin condenses into chromosomes; spindle fibres begin to form; nucleolus disappears; nuclear envelope starts to break down.
MetaphaseChromosomes align at the metaphase plate (equatorial plane); spindle fibres attach to centromeres. Best stage to count chromosomes.
AnaphaseCentromeres split; sister chromatids pulled to opposite poles by spindle. Number of chromosomes doubles transiently.
TelophaseNuclear envelope reforms around each set; chromosomes decondense; nucleolus reappears.
CytokinesisAnimal cells: cleavage furrow (actin ring). Plant cells: cell plate formed by Golgi vesicles.

3. Meiosis — Overview and Significance

Meiosis produces four haploid daughter cells from one diploid parent cell. It occurs in reproductive organs during gamete formation. Meiosis has two sequential divisions:

  • Meiosis I (reductional division) — homologous chromosomes separate → chromosome number halved.
  • Meiosis II (equational division) — sister chromatids separate → similar to mitosis.

Significance:

  • Maintains chromosome number across generations in sexually reproducing organisms.
  • Introduces genetic variation via crossing over and independent assortment.
NEET tip: Meiosis I is reductional; Meiosis II is equational (like mitosis). At the END of Meiosis I — cells are haploid but each chromosome still has two sister chromatids. DNA content and chromosome number become truly haploid only after Meiosis II.

4. Meiosis I — Prophase I in Detail

Prophase I is the longest and most complex phase of meiosis. It is divided into five substages (LZPDDIA):

SubstageKey events
LeptoteneChromosomes begin to condense; become visible as thin threads.
ZygoteneSynapsis — homologous chromosomes pair up; synaptonemal complex forms; the paired structure = bivalent (tetrad).
PachyteneCrossing over — exchange of segments between non-sister chromatids of homologous chromosomes at chiasmata; recombination nodules visible.
DiploteneSynaptonemal complex dissolves; homologs remain attached at chiasmata; terminalisation of chiasmata begins.
DiakinesisChromosomes maximally condensed; nuclear envelope breaks; spindle forms; chiasmata move to chromosome ends.
NEET caution: Crossing over occurs during Pachytene (not Zygotene). The chiasmata (cross-shaped structures) are visible in Diplotene but are the sites where crossing over already occurred in Pachytene.

5. Mitosis vs Meiosis — Key Comparisons

FeatureMitosisMeiosis
Where occursSomatic cellsGermline cells (gonads)
DivisionsOneTwo
Daughter cells2, diploid (2n)4, haploid (n)
Chromosome pairingNo synapsisSynapsis in Meiosis I
Crossing overNoYes (Pachytene)
Genetic outcomeIdenticalVaried (recombination)
PurposeGrowth, repair, asexual repro.Sexual reproduction, gametes
Deep Revision

High-Yield Concept Depth

Use this section after the first reading. It connects facts into mechanisms, comparisons, and NEET-style decision rules.

Cell Cycle Checkpoint Logic

G1 is growth and decision-making, S is DNA synthesis, G2 is preparation for mitosis, and M phase is actual division. G0 is a quiescent exit from active cycling. A cell should not enter mitosis unless DNA replication and repair are complete.

NEET cue: DNA amount doubles in S phase, but chromosome number does not double until sister chromatids separate.

Meiosis Event Map

Leptotene condenses chromosomes. Zygotene pairs homologues by synapsis. Pachytene performs crossing over. Diplotene shows chiasmata. Diakinesis completes terminalisation and prepares for metaphase I.

The single most tested confusion: crossing over happens in pachytene, while chiasmata are clearly seen in diplotene.

Study System

How to Master This Chapter

Use this process after reading the notes. It turns NCERT lines into exam-ready recall, diagrams, and MCQ decisions.

NCERT to MCQ Flow

  1. Read one NCERT paragraph and underline the exact term.
  2. Convert it into a one-line cause-effect rule.
  3. Attach one example, diagram label, exception, or comparison.
  4. Solve five MCQs from the same subtopic immediately.
  5. Write why each wrong option is wrong, not only why the answer is right.

Mistake Repair

Memory mistake: make a two-column comparison table.

Diagram mistake: redraw the labelled structure from memory.

Process mistake: rewrite the sequence with arrows.

Assertion-reason mistake: check truth of each statement first, then relation.

Easy Examples for Quick Revision

Practice these before starting MCQs. They are designed to lock core concepts with minimum theory load.

Example 1: DNA replication occurs in which phase?

S phase of interphase.

Example 2: Best mitotic stage to count chromosomes?

Metaphase.

Example 3: Crossing over occurs in which prophase I substage?

Pachytene.

Example 4: Chiasmata become visible in which stage?

Diplotene.

Example 5: Meiosis I is reductional or equational?

Reductional, because homologous chromosomes separate and chromosome number halves.

NEET Bio Cell Cycle Notes
NEET Biology Revision

Chapter note placement for Cell Cycle and Cell Division.

Practice Tests

The Practice Zone

Test your understanding of Cell Cycle and Cell Division with focused sectional tests and a full-length NEET-style module test. Each chapter now runs 5 practice tests of 25 questions each, and every question has a 90-second timer — matching real NEET exam pacing.

Session Tests

5 focused sessions: cell cycle phases, mitosis events, meiosis overview, Prophase I substages, and mitosis vs meiosis comparison — 25 NEET-style MCQs each.

Open Session Tests

Full-Length Mock

NEET-style 125-question module test on Cell Cycle and Cell Division with timer, palette, answer review, and subtopic accuracy breakdown.

Open Full Mock
NEET Bio Cell Cycle Notes Practice
NEET Practice Sponsor

Inline banner shown in the practice section — high-intent placement for test-prep and coaching campaigns.

Up Next
Transport in Plants
Next Chapter →
Finished this topic?

Keep the practice loop moving

Move straight from chapter-wise questions into a subject test, then loop back into weaker areas instead of ending the session here.

Try Full NEET Mock