Loading of phloem is related to

Options

A. increase of sugar in phloem
B. elongation of phloem cells
C. separation of phloem parenchyma
D. strengthering of phloem fibres

Explanation

### Step-by-Step Solution:

1. **Understanding Phloem Loading**:
- Phloem loading refers to the process of transporting sugars (mainly sucrose) into the phloem from the source, which is typically the leaves where photosynthesis occurs.

2. **Role of Photosynthesis**:
- In the leaves, during photosynthesis, glucose is produced. However, glucose is not transported directly; it is converted into sucrose for efficient transport through the phloem.

3. **Source and Sink Concept**:
- The source is where the sugars are synthesized (leaves), and the sink is where they are utilized or stored (roots, stems, or growing tissues).

4. **Active Transport Mechanism**:
- The loading of sucrose into the phloem occurs through active transport, which requires energy. This process creates a high concentration of sucrose in the phloem at the source.

5. **Pressure Flow Hypothesis**:
- According to the pressure flow hypothesis (or mass flow hypothesis), the high concentration of sucrose in the phloem creates a pressure gradient that drives the flow of sap from the source (high pressure) to the sink (low pressure).

6. **Identifying the Correct Option**:
- Among the given options, the increase of sugar in the phloem is directly related to the loading process. The other options (elongation of phloem cells, separation of phloem parenchyma, strengthening of phloem fibers) do not pertain to the loading of phloem.

7. **Conclusion**:
- Therefore, the correct answer to the question "Loading of phloem is related to" is the increase of sugar in the phloem.