When a potassium ion (`K^(+)`) passes from the soil into the vacuole of a root cell, it encounters some cellular barriers. Which of the following is the most direct path the `K^(+)` would take through these barriers?

Options

A. Primary cell wall `rarr` secondary cell wall `rarr` tonoplast
B. Secondary cell wall `rarr` plasma membrane `rarr` thylakoid
C. Primary cell wall `rarr` plasma membrane `rarr` tonoplast
D. Cell wallplasma `rarr` plasma membrane `rarr` tonoplast `rarr` grana

Answer

To determine the most direct path a potassium ion (`K^(+)`) takes from the soil into the vacuole of a root cell, we need to analyze the cellular barriers it encounters. Here’s the step-by-step solution:

### Step-by-Step Solution:

1. **Entry from Soil**: The potassium ion (`K^(+)`) begins its journey in the soil and is absorbed by the root cells. The first layer it encounters is the **primary cell wall** of the epidermal cells of the root.

2. **Crossing the Primary Cell Wall**: The potassium ion passes through the **primary cell wall**. This wall is porous and allows the movement of ions.

3. **Plasma Membrane**: After crossing the primary cell wall, the `K^(+)` ion encounters the **plasma membrane** of the root cell. The plasma membrane is semi-permeable and does not allow ions to pass freely.

4. **Transport Proteins**: To facilitate the movement of the `K^(+)` ion across the plasma membrane, it utilizes **channel proteins** or **transport proteins**. This process is known as **active transport**, which requires energy (ATP) to move the ion into the cytoplasm of the cell.

5. **Cytoplasm**: Once inside the cell, the `K^(+)` ion is now in the **cytoplasm**.

6. **Tonoplast**: The next barrier the ion encounters is the **tonoplast**, which is the membrane surrounding the vacuole. The `K^(+)` ion must cross this membrane to enter the vacuole.

7. **Vacuole**: Finally, after passing through the tonoplast, the `K^(+)` ion enters the **vacuole**, which is its final destination.

### Conclusion:
The most direct path for the potassium ion (`K^(+)`) is:
- Primary Cell Wall → Plasma Membrane → Tonoplast

Thus, the correct answer is option number 3: **Primary Cell Wall, Plasma Membrane, Tonoplast**.