Munch's mass flow hypothesis explains

Options

A. water flow in xylem
B. horizontal flow of water from cortex to xylem
C. translocation of solutes through phloem
D. absorption of water by roots .

Answer

**Step-by-Step Solution:**

1. **Understanding Munch's Mass Flow Hypothesis:**
- Munch's mass flow hypothesis, also known as the pressure flow hypothesis, explains the mechanism of translocation of sugars in plants, particularly from the source (leaves) to the sink (areas of consumption like roots, fruits, etc.).

2. **Identifying the Source and Sink:**
- The source is where sugars are produced, primarily in the leaves through photosynthesis. The sink is where these sugars are utilized or stored.

3. **Loading of Sugars:**
- Sugars (mainly in the form of sucrose) are actively transported from the source into the companion cells and then into the phloem sieve tube elements. This process is known as loading and occurs under hypertonic conditions, which means that the concentration of solutes (sugars) is higher in the phloem than in the surrounding cells.

4. **Water Movement:**
- Due to the hypertonic condition created by the high concentration of sugars, water from the adjacent xylem enters the phloem. This influx of water increases the pressure within the phloem.

5. **Pressure Flow:**
- The increased pressure in the phloem causes the sap (sugar solution) to move towards areas of lower pressure, which are the sinks. At the sink, sugars are actively transported out of the phloem, leading to a decrease in pressure.

6. **Conclusion:**
- Thus, Munch's mass flow hypothesis explains the translocation of solutes (specifically sugars) through the phloem from the source to the sink, driven by pressure differences.

**Final Answer:**
- Munch's mass flow hypothesis explains the translocation of solutes through the phloem.

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