Match List I with List II: List I (Phase of cell cycle) i. G1 phase ii. S phase iii. G2 phase iv. M phase List II (Activity) a. Actual cell division occurs b. Cell is metabolically active and continuously grows but does not replicate its DNA c. Synthesis of DNA occurs and the amount of DNA per cell doubles d. Proteins are synthesized while cell growth continues Choose the correct answer from the options given below:

i – b, ii – c, iii – d, iv – a

i – c, ii – d, iii – a, iv – b

i – a, ii – b, iii – c, iv – d

i – d, ii – a, iii – b, iv – c

Cell Cycle Phases

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NCERT Class 11 · Cell Cycle and Cell Division · 3 NEET questions

Most students mistake Interphase for a 'resting' phase. It is the most metabolically active period of the cell cycle. If DNA replication in the S-phase is flawed, the cell is doomed to apoptosis or malignancy.

The idea

The cell cycle is divided into Interphase and the M phase. Interphase consists of G1, S, and G2 phases, where the cell grows and replicates its DNA. The M phase represents the actual division, involving karyokinesis and cytokinesis. This sequence is strictly regulated to ensure genetic stability.

Why it matters

It ensures that the cell grows, replicates its DNA, and divides accurately to maintain the integrity of the organism.

NEET lens

NEET focuses on the duration of phases and the specific events in each. Memorize that DNA content doubles in S-phase, but chromosome number remains the same. Do not confuse G0 phase with Interphase; it is a quiescent stage. Expect questions on the sequence of events and the metabolic state of the cell.

Clinical significance

Uncontrolled cell cycle progression is the hallmark of cancer. Mutations in cell cycle checkpoints, particularly those regulating the G1/S transition, lead to the formation of tumors. Chemotherapy drugs like Methotrexate specifically target these phases to halt rapid cell division.

Introduction

The cell cycle is the ordered sequence of events by which a cell grows and divides into two daughter cells. It consists of Interphase (G1 + S + G2) and M phase (mitosis + cytokinesis).

Core concept

Four phases: G1 (gap 1, first growth, longest and most variable), S (DNA synthesis/replication), G2 (gap 2, second growth, preparation for division), M (mitosis + cytokinesis, shortest). The entire cycle takes ~24 hours in rapidly dividing human cells. G1 is most variable — cells can pause here or exit to G0. Cell cycle checkpoints: G1/S, G2/M, M (spindle assembly).

Go deeper

Cyclins and CDKs (cyclin-dependent kinases) drive cell cycle progression. Different cyclin-CDK complexes are active at different phases: Cyclin D-CDK4/6 in G1, Cyclin E-CDK2 at G1/S transition, Cyclin A-CDK2 in S, Cyclin B-CDK1 (MPF, maturation promoting factor) at G2/M.

From Class 10

Cell division is a carefully ordered process. The cell cycle describes all the stages a cell goes through from one division to the next.