The function of nucleated cells in phloem is to ______

Options

A. provide energy to sieve elements for active transport
B. provide water to phloem
C. load sucrose into sieve elements by passive transport
D. load sucrose into sieve elements by active transport

Answer

### Step-by-Step Solution:

1. **Understanding Phloem Structure**: Phloem is a type of vascular tissue in plants responsible for the transport of nutrients, particularly sucrose. It consists of four main types of cells:
- Phloem parenchyma
- Companion cells
- Sieve tube elements
- Phloem fibers

2. **Identifying Nucleated Cells**: Among these cell types, companion cells are the nucleated cells in the phloem. They have a nucleus, which distinguishes them from sieve tube elements that lack a nucleus.

3. **Function of Companion Cells**: The primary function of companion cells is to support the sieve tube elements. They play a crucial role in the transport of sugars (sucrose) from the source (where sugars are produced) to the sink (where sugars are utilized).

4. **Mechanism of Sugar Loading**: Companion cells assist in loading sucrose into the sieve tube elements. This process can occur via two mechanisms:
- Passive transport (diffusion)
- Active transport (which requires energy)

5. **Determining the Correct Answer**: The question specifically asks for the function of nucleated cells in phloem. Since companion cells are responsible for loading sucrose into the sieve elements and they do so primarily through active transport, the correct answer is:
- **Option D**: Load sucrose into sieve element by active transport.