Which part in roots has transport proteins that are control points, where a plant adjust the quantity & types of solutes that reach the xylem :

Options

A. Cortical cells
B. Endodermal cells
C. Epidermal cells
D. Root hairs

Answer

To answer the question regarding which part of the roots contains transport proteins that act as control points for adjusting the quantity and types of solutes reaching the xylem, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for a specific part of the root that has transport proteins functioning as control points for solute regulation.

2. **Analyzing the Options**:
- **Option 1: Cortical Cells**: These are unspecialized cells located between the epidermis and vascular tissue. Their primary role is to regulate water flow, but they do not specifically control solute types and quantities reaching the xylem. Thus, this option is incorrect.

- **Option 2: Endodermal Cells**: These cells are located in the endodermis, which is the innermost layer of the cortex in roots. Endodermal cells contain transport proteins that selectively allow water and nutrients to pass into the xylem. They act as control points, regulating the amount and types of solutes that enter the vascular system. This makes this option the correct answer.

- **Option 3: Epidermal Cells**: The epidermis serves as a protective layer and does not play a significant role in solute transport to the xylem. Therefore, this option is incorrect.

- **Option 4: Root Hairs**: Root hairs are extensions of root epidermal cells that increase surface area for absorption of water and minerals. While they are important for nutrient uptake, they do not function as control points for solute transport to the xylem. Thus, this option is also incorrect.

3. **Conclusion**: After analyzing all options, the correct answer is **Option 2: Endodermal Cells**, as they are responsible for regulating the entry of solutes into the xylem.

### Final Answer:
**The part in roots that has transport proteins which are control points for adjusting the quantity and types of solutes that reach the xylem is the Endodermal Cells.**

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