The functions of (A)____ are controlled by the (B)____ of companion cells.

Answer

To answer the question, we need to identify the components involved and their relationship in the context of plant anatomy, specifically in the phloem tissue.

### Step-by-Step Solution:

1. **Identify the Components**:
- The question mentions two components: (A) and (B). We need to determine what these components are in relation to companion cells.

2. **Understand Companion Cells**:
- Companion cells are specialized cells found in the phloem tissue of plants. They are closely associated with sieve tube elements, which are responsible for the transport of nutrients, particularly sugars.

3. **Function of Companion Cells**:
- Companion cells play a crucial role in supporting the sieve tube elements. They provide metabolic support and help in the regulation of the sieve tubes' functions.

4. **Identify the Function of Sieve Tubes**:
- Sieve tubes are responsible for the translocation of food (mainly sugars) throughout the plant. However, they lack a nucleus and rely on companion cells for their metabolic functions.

5. **Determine the Relationship**:
- The functions of the sieve tube elements (A) are controlled by the nucleus of the companion cells (B). The nucleus of the companion cells regulates the activities of the sieve tubes through various mechanisms, including the exchange of materials through plasmodesmata (cytoplasmic connections).

6. **Fill in the Blanks**:
- Based on the analysis, we can fill in the blanks:
- (A) = Sieve Tube
- (B) = Nucleus

### Final Answer:
The functions of (A) **sieve tube** are controlled by the (B) **nucleus** of companion cells.

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