Which of the following is a difference between transport by xylem and transport by phloem?

Options

A. Active transport moves xylem but not phloem sap
B. Transpiration moves phloem sap but not xylem sap
C. xylem sap moves up, phloem sap moves up and down
D. xylem moves from sugar source to sink but phloem does not

Answer

To answer the question regarding the differences between transport by xylem and transport by phloem, we can break down the key aspects of each transport system in plants.

### Step-by-Step Solution:

1. **Understanding Xylem Transport**:
- Xylem primarily transports water and dissolved minerals from the roots to the rest of the plant.
- The movement of xylem sap is largely unidirectional, meaning it only moves upwards.

2. **Understanding Phloem Transport**:
- Phloem transports organic nutrients, particularly sugars produced during photosynthesis, from the leaves (source) to other parts of the plant (sink).
- The movement of phloem sap is bidirectional, meaning it can move both upwards and downwards.

3. **Direction of Flow**:
- Xylem sap flows only in one direction (upwards).
- Phloem sap can flow in multiple directions (up and down).

4. **Mechanism of Transport**:
- Xylem transport is primarily passive, relying on processes like transpiration to create a negative pressure that pulls water up.
- Phloem transport involves active transport mechanisms, especially in loading and unloading sugars, which require energy.

5. **Substances Transported**:
- Xylem mainly carries water and minerals.
- Phloem carries organic compounds, mainly sugars.

6. **Conclusion**:
- The main differences between xylem and phloem transport are:
- Xylem is unidirectional (upwards) while phloem is bidirectional (up and down).
- Xylem primarily transports water and minerals, while phloem transports organic nutrients.

### Final Answer:
The key differences between transport by xylem and transport by phloem are:
- Xylem sap moves unidirectionally (upwards) while phloem sap moves bidirectionally (up and down).
- Xylem primarily transports water and minerals, whereas phloem transports sugars and other organic nutrients.