Consider the following statements
1. Xylem vessels are semi-permeable
2. Sieve tubes translocate only solutes
3. Xylem vessels do not have a turgor pressure
4. Companion cells help in maintaining pressure gradient in the sieve tubes .
Which of the statements given above are correct ?

Options

A. 1 and 2
B. 2 and 3
C. 1 and 3
D. 2 and 4

Answer

To determine which of the given statements about xylem vessels and sieve tubes are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyzing Statement 1: "Xylem vessels are semi-permeable."**
- Xylem vessels are primarily responsible for the conduction of water and minerals. They consist of dead cells (tracheids and vessel elements) that have lignified walls. These walls do not allow selective permeability as they lack a living cell membrane. Therefore, this statement is **incorrect**.

2. **Analyzing Statement 2: "Sieve tubes translocate only solutes."**
- Sieve tubes, which are part of the phloem, are responsible for the transport of organic substances (solutes) such as sugars. They do not conduct water like xylem vessels. Since they primarily translocate solutes, this statement is **correct**.

3. **Analyzing Statement 3: "Xylem vessels do not have a turgor pressure."**
- Turgor pressure is essential for the functioning of xylem vessels. It helps in the upward movement of water and minerals. Xylem vessels do experience turgor pressure due to the water that fills them. Therefore, this statement is **incorrect**.

4. **Analyzing Statement 4: "Companion cells help in maintaining pressure gradient in the sieve tubes."**
- Companion cells are closely associated with sieve tubes and play a crucial role in maintaining the pressure gradient necessary for the translocation of substances. They have a nucleus and support the sieve tubes, which lack a nucleus. Thus, this statement is **correct**.

### Conclusion:
The correct statements are:
- Statement 2: "Sieve tubes translocate only solutes." (Correct)
- Statement 4: "Companion cells help in maintaining pressure gradient in the sieve tubes." (Correct)

### Final Answer:
The correct statements are 2 and 4.

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