Questions & explanations
1. Which of the following correctly describes the cell cycle?
- A series of events that take place in a cell from one mitotic division to the next
- The process of DNA replication only
- The period between two meiotic divisions
- The time taken for a cell to undergo apoptosis
Answer: A series of events that take place in a cell from one mitotic division to the next
The cell cycle is defined as the sequence of events from one cell division to the next, including interphase and mitosis. Option A correctly captures this definition. Option B is incorrect because DNA replication is only one part of the S phase. Option C is incorrect because the cell cycle includes mitotic divisions, not just meiotic. Option D is incorrect because apoptosis is programmed cell death, not part of the cell cycle.
2. Which of the following is a function of cell cycle checkpoints?
- To ensure DNA replication is complete before mitosis
- To trigger apoptosis in all cells
- To speed up the cell cycle
- To prevent any cell from dividing
Answer: To ensure DNA replication is complete before mitosis
Cell cycle checkpoints monitor and ensure proper completion of key events. For example, the G2 checkpoint checks for complete DNA replication before mitosis. Option B is incorrect because apoptosis is not triggered at checkpoints routinely. Option C is opposite; checkpoints can delay the cycle. Option D is false; checkpoints allow division if conditions are met.
3. The M phase of the cell cycle includes which two main processes?
- Karyokinesis and cytokinesis
- DNA replication and transcription
- Cell growth and protein synthesis
- Chromosome condensation and decondensation
Answer: Karyokinesis and cytokinesis
M phase consists of mitosis (karyokinesis, division of the nucleus) and cytokinesis (division of the cytoplasm). DNA replication occurs in S phase, cell growth in G1, and chromosome condensation is part of prophase but not the entire M phase. Thus, option A is correct.
4. Which event is characteristic of the S phase of the cell cycle?
- Cell growth and protein synthesis
- DNA replication and doubling of DNA content
- Preparation for mitosis and spindle formation
- Separation of sister chromatids
Answer: DNA replication and doubling of DNA content
The S phase is specifically when DNA replication occurs, resulting in the doubling of DNA content. Option A describes G1 phase, option C describes G2 phase, and option D describes anaphase of mitosis. Thus, option B is correct.
5. Which of the following occurs during the G1 phase of the cell cycle?
- DNA replication
- Cell growth and synthesis of proteins
- Formation of the mitotic spindle
- Cytokinesis
Answer: Cell growth and synthesis of proteins
G1 phase is characterized by cell growth and the synthesis of proteins and organelles. DNA replication occurs in S phase, spindle formation in G2/prophase, and cytokinesis at the end of M phase. Therefore, option B is correct.
6. During which phase of the cell cycle does DNA replication occur?
- G1 phase
- S phase
- G2 phase
- M phase
Answer: S phase
The S phase (synthesis phase) is when DNA replication takes place, doubling the DNA content. G1 phase is for cell growth, G2 phase is for preparation for mitosis, and M phase is mitosis itself. Therefore, option B is correct.
7. Cells that exit the active cell cycle and enter a non-dividing state are said to be in which phase?
- G1 phase
- S phase
- G0 phase
- G2 phase
Answer: G0 phase
The G0 phase is a quiescent stage where cells have left the active cell cycle and are not dividing. They may re-enter the cycle if stimulated. G1, S, and G2 are all active phases of the cell cycle. Hence, option C is correct.
8. In a typical human cell, the cell cycle duration is approximately:
- 12 hours
- 24 hours
- 48 hours
- 72 hours
Answer: 24 hours
A typical human cell in culture completes the cell cycle in about 24 hours. This can vary, but 24 hours is the standard reference. Options A, C, and D are not typical for human cells.