## **Core Concept**
The question tests the understanding of cell membrane transport mechanisms, specifically the classification based on energy requirements. Cell membrane transport can be categorized into passive transport (which does not require energy) and active transport (which requires energy). The key concept here is the role of energy in transporting molecules across the cell membrane.

## **Why the Correct Answer is Right**
Active transport is a type of transport across the cell membrane that requires the expenditure of energy. This energy is often in the form of ATP. Active transport mechanisms include pumps like the sodium-potassium pump, which moves sodium out and potassium into the cell against their concentration gradients, a process critical for maintaining cell membrane potential and proper ion balance. This process is essential for various cellular functions, including nerve impulse transmission and muscle contraction.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is blank and does not provide a viable choice for evaluation.
- **Option B:** This option is also blank and cannot be assessed.
- **Option C:** Similarly, this option is blank and lacks the necessary information for analysis.
- **Option D:** This option is blank as well, making it impossible to evaluate.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that active transport is crucial for maintaining the internal environment of the cell, including ion balance and nutrient uptake against concentration gradients. A classic example of active transport is the **sodium-potassium pump** (Na+/K+-ATPase), which uses ATP to transport sodium out of the cell and potassium into the cell.

## **Correct Answer:** . Active transport