Which of the following statements is incorrect about companion cell?

Options

A. It is a specialised parenchymatous cell
B. Its nucleus controls the function of sieve tube
C. It helps in maintaining the pressure gradient in sieve tube
D. It is present in all vascular plants having phloem

Answer

To determine which statement about companion cells is incorrect, we will analyze each option provided:

1. **Option 1: It is specialized parenchyma cells.**
- Companion cells are indeed specialized cells that are derived from the same parent cell as sieve tube elements. They are part of the phloem tissue and play a crucial role in the transport of nutrients.

2. **Option 2: The nucleus controls the function of CO2.**
- This statement is misleading. Companion cells do have a nucleus, but they do not specifically control the function of CO2. Instead, they assist in the transport of sugars and other organic compounds in the phloem.

3. **Option 3: It helps in maintaining the pressure gradient in CO2.**
- This statement is incorrect. Companion cells do not maintain a pressure gradient specifically for CO2. They are involved in maintaining the pressure gradient for the transport of phloem sap, which primarily consists of sugars, not CO2.

4. **Option 4: It helps in maintaining the pressure gradient in CO2.**
- Similar to option 3, this statement is also incorrect for the same reason. Companion cells are not directly involved in maintaining a pressure gradient for CO2.

After analyzing all the options, we can conclude that the incorrect statements are options 2, 3, and 4, but since the question asks for a singular incorrect statement, we can highlight option 2 as the most misleading.

### Final Answer:
The incorrect statement about companion cells is: **Option 2: The nucleus controls the function of CO2.**