When do viscosity and refractivity of cytoplasm increase ?

Options

A. `G_(1)`-phase
B. S-phase
C. Prophase
D. Metaphase

Answer

**Step-by-Step Solution:**

1. **Understanding Viscosity and Refractivity:**
- Viscosity refers to the thickness or resistance to flow of a fluid. In the context of cytoplasm, higher viscosity means that the cytoplasm becomes thicker and flows less easily.
- Refractivity refers to the bending of light as it passes through a substance. An increase in refractivity indicates that the substance is becoming denser or more concentrated.

2. **Identifying the Phase of Cell Division:**
- The question asks during which phase of the cell cycle the viscosity and refractivity of the cytoplasm increase.
- The phases of the cell cycle include Interphase (G1, S, G2) and Mitosis (Prophase, Metaphase, Anaphase, Telophase).

3. **Analyzing the Prophase:**
- During Prophase, chromatin condenses to form distinct chromosomes. This process involves the compaction of genetic material, which leads to changes in the cytoplasm.
- As chromatin condenses, the cytoplasm's flow becomes more restrained, leading to an increase in viscosity.

4. **Conclusion:**
- Based on the condensation of chromatin and the formation of chromosomes during Prophase, it is concluded that both viscosity and refractivity of the cytoplasm increase during this phase.
- Therefore, the correct answer is **Prophase (Option C)**.

---