Cell Cycle Phases and Division Processes — NEET Biology

Correct answer: A — 5, 1, 2, 3, 6, 4

This question requires arranging key events of interphase (G₁, S, G₂) in their chronological order. Interphase consists of G₁, S, and G₂ phases in that sequence. - G₁ phase (Gap 1) is the interval between mitosis and the initiation of DNA replication. During this phase, the cell is metabolically active and continuously grows. - S phase (Synthesis) is when DNA replication occurs, doubling the DNA content. In animal cells, centriole duplication also occurs during S phase. - G₂ phase (Gap 2) is when proteins are synthesized in preparation for mitosis, and cell growth continues. Let's map the given events to their respective phases: 1. Continuous cell growth and normal metabolic activity: G₁ phase (occurs throughout G₁). 2. Centriole duplication in animal cells: S phase (occurs in cytoplasm during S phase). 3. DNA synthesis leading to doubling of DNA content: S phase (the defining event of S phase). 4. Synthesis of proteins necessary for spindle formation: G₂ phase (proteins for mitosis are synthesized). 5. Interval after M phase and before S phase: G₁ phase (This precisely defines G₁). 6. Cell growth continues in preparation for mitosis: G₂ phase (cell growth continues in G₂). Chronological order of events: - First, the cell is in G₁ phase: Events 5 and 1 happen (5 defines the period, 1 describes activity). So, 5 then 1. - Next, the cell enters S phase: Events 2 and 3 happen (2 is centriole duplication, 3 is DNA synthesis). So, 2 then 3. - Finally, the cell enters G₂ phase: Events 6 and 4 happen (6 is continued growth, 4 is protein synthesis for mitosis). So, 6 then 4. The correct chronological order is 5, 1, 2, 3, 6, 4.