The main difference between active and passive transport across cell membrane is that the

Options

A. Passive transport is active
B. Active transport is passtive
C. Passive transport is gradient based, while active transport is energy based against concentration gradient
D. Passive transport is confined to anions, while active transport is for cations only

Answer

To answer the question about the main difference between active and passive transport across the cell membrane, we can break it down into clear steps:

### Step-by-Step Solution:

1. **Definition of Active Transport**:
- Active transport is the process by which substances move across the cell membrane against their concentration gradient. This means that molecules move from an area of lower concentration to an area of higher concentration.
- This process requires energy, usually in the form of ATP (adenosine triphosphate).

2. **Definition of Passive Transport**:
- Passive transport is the movement of substances across the cell membrane without the need for energy. This occurs along the concentration gradient, meaning substances move from an area of higher concentration to an area of lower concentration.
- Examples of passive transport include simple diffusion and facilitated diffusion.

3. **Energy Requirement**:
- Active transport requires energy input because it is moving substances against their natural flow (from low to high concentration).
- Passive transport does not require energy since it relies on the natural tendency of molecules to move from areas of high concentration to areas of low concentration.

4. **Direction of Movement**:
- In active transport, the movement is against the concentration gradient (low to high).
- In passive transport, the movement is along the concentration gradient (high to low).

5. **Types of Molecules Transported**:
- Active transport can involve various types of molecules, including ions (cations and anions), depending on the specific transport mechanism.
- Passive transport can also involve various types of molecules, but it is generally not restricted to specific types like anions or cations.

### Conclusion:
The main difference between active and passive transport across the cell membrane is that **active transport requires energy to move substances against their concentration gradient, while passive transport occurs naturally along the concentration gradient without the need for energy**.

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