Increase in temperature

Options

A. Increases osmotic pressure
B. Decreases osmotic pressure
C. Has no effect on osmotic pressure
D. Causes endosmosis

Answer

### Step-by-Step Solution:

1. **Understanding Mass Flow Hypothesis**: The mass flow hypothesis explains how nutrients, particularly sucrose, are transported in the phloem of plants. It is based on the concept of pressure flow, where differences in pressure drive the movement of sap.

2. **Loading of Phloem**: The process begins with the loading of sucrose into the phloem from the source (usually leaves). This loading decreases the water potential in the phloem, causing water to move in from the adjacent xylem due to osmosis.

3. **Creation of Hydrostatic Pressure**: As water enters the phloem, it increases the turgor pressure within the sieve tubes. This pressure is what drives the movement of the sap through the phloem.

4. **Bidirectional Movement**: The movement of sucrose in the phloem can occur in both directions (from source to sink and vice versa), depending on the plant's needs.

5. **Evaluating the Statements**:
- **Loading of Phloem**: This statement is correct as it sets up a water potential gradient.
- **Transported Sugar**: The sugar transported is indeed sucrose, which is also correct.
- **Pressure Flow Stops**: The statement that "as hydrostatic pressure in the phloem sieve tube increases, pressure flow stops and sap accumulates in the phloem" is incorrect. According to the mass flow hypothesis, pressure flow does not stop; instead, it continues as long as there is a gradient.

6. **Conclusion**: The incorrect statement regarding the mass flow hypothesis is that pressure flow stops and sap accumulates in the phloem when hydrostatic pressure increases. Instead, the pressure flow continues due to the maintained gradient.

### Final Answer:
The statement that is not correct for the mass flow hypothesis is: "As hydrostatic pressure in phloem sieve tube increases, pressure flow stops and sap accumulates in the phloem."

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