Which one of the following process of transporting substances across a membrane does not involve a change in shape of the transport protein

Options

A. Active transport
B. `Na^(+) -K^(+)` pump
C. Simple diffusion
D. Facilitated diffusion

Explanation

To solve the question "Which one of the following processes of transporting substances across a membrane does not involve a change in shape of the transport protein?", we need to analyze the options provided:

1. **Active Transport**
2. **Sodium-Potassium Pump**
3. **Simple Diffusion**
4. **Facilitated Diffusion**

### Step-by-Step Solution:

**Step 1: Understand the Processes**
- **Active Transport**: This process requires energy to move substances against their concentration gradient. It involves transport proteins that change shape to facilitate the movement of molecules.

- **Sodium-Potassium Pump**: This is a specific type of active transport that moves sodium ions out of the cell and potassium ions into the cell. It also involves a change in the shape of the transport protein.

- **Facilitated Diffusion**: This process allows substances to cross membranes with the help of transport proteins (either carrier proteins or channel proteins) but does not require energy. However, the transport proteins still change shape during this process.

- **Simple Diffusion**: This is the movement of molecules from an area of higher concentration to an area of lower concentration without the need for transport proteins. It does not involve any change in the shape of proteins because it does not require them.

**Step 2: Identify the Correct Answer**
From the analysis:
- Active transport, sodium-potassium pump, and facilitated diffusion all involve a change in the shape of the transport proteins.
- Simple diffusion does not involve any transport proteins and therefore does not involve a change in shape.

Thus, the correct answer is **Simple Diffusion**.

### Final Answer:
**Simple Diffusion**

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