Which factor influences activ transport of substances across the membrane ?

Explanation

### Step-by-Step Text Solution:

1. **Understanding Active Transport**: Active transport is a process that moves substances across a cell membrane against their concentration gradient, meaning from an area of lower concentration to an area of higher concentration. This process requires energy, typically in the form of ATP (adenosine triphosphate).

2. **Role of Energy**: The energy required for active transport is crucial because it allows cells to accumulate substances that are necessary for their functions, even when those substances are in lower concentrations outside the cell.

3. **Protein Transporters**: Active transport relies on specific proteins known as transporters or pumps. These proteins facilitate the movement of molecules across the membrane. A well-known example is the sodium-potassium pump, which transports sodium ions out of the cell and potassium ions into the cell.

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