**Previous Year Questions (2019-16) - Cell Cycle and Cell Division**

Cell cycle and cell division are important topics in the NEET syllabus. Here, we will discuss some previous year questions related to these topics.

**Question 1 (2019):**
Describe the cell cycle and explain the significance of checkpoints in the cell cycle.

**Answer:**
The cell cycle is a series of events that occur in a cell leading to its division and duplication. It consists of four main phases: G1 (gap 1), S (synthesis), G2 (gap 2), and M (mitotic) phase.

- G1 Phase: The cell grows and carries out its normal functions.
- S Phase: DNA replication occurs, resulting in the duplication of chromosomes.
- G2 Phase: The cell prepares for division by synthesizing proteins and organelles.
- M Phase: The cell divides into two daughter cells through mitosis and cytokinesis.

**Significance of Checkpoints in the Cell Cycle:**
Checkpoints are crucial in the cell cycle as they ensure that each phase is completed accurately before progressing to the next. There are three main checkpoints:

1. G1 Checkpoint: Also known as the restriction point, it determines whether the cell will continue with the cell cycle or enter a resting phase (G0). It checks for cell size, nutrient availability, DNA damage, and growth factors.
2. G2 Checkpoint: It ensures that DNA replication is complete and checks for any DNA damage before entering mitosis.
3. M Checkpoint: This checkpoint occurs during metaphase and ensures that all chromosomes are properly attached to the spindle fibers before the cell proceeds to anaphase.

These checkpoints prevent the cell from proceeding to the next phase if any abnormalities or errors are detected. They help maintain genomic integrity, prevent the formation of abnormal cells, and ensure proper cell division.

**Question 2 (2018):**
Differentiate between mitosis and meiosis.

**Answer:**
Mitosis and meiosis are two types of cell divisions, but they differ in their purpose and outcome.

**Mitosis:**
- Purpose: Mitosis is involved in the growth, repair, and asexual reproduction of organisms.
- Outcome: It results in the production of two genetically identical daughter cells.
- Number of Divisions: One division.
- Chromosome Number: The daughter cells have the same number of chromosomes as the parent cell.
- Phases: Mitosis consists of four phases - prophase, metaphase, anaphase, and telophase.
- Crossing Over: Absent in mitosis.

**Meiosis:**
- Purpose: Meiosis is involved in the production of gametes (sex cells) for sexual reproduction.
- Outcome: It results in the production of four genetically unique daughter cells.
- Number of Divisions: Two divisions (meiosis I and meiosis II).
- Chromosome Number: The daughter cells have half the number of chromosomes as the parent cell.
- Phases: Meiosis consists of eight phases - prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, and telophase II.
- Crossing Over: Occurs during prophase I, leading to genetic variation.

**Question 3 (2017):**
What is the significance of cytokinesis in the cell cycle?

**Answer:**
Cytokinesis is