What are pumps in active transport?

Explanation

### Step-by-Step Text Solution:

1. **Definition of Active Transport**: Active transport is a biological process that requires energy to move molecules across a cell membrane. This movement is against the concentration gradient, meaning substances are moved from an area of lower concentration to an area of higher concentration.

2. **Role of Pumps**: In the context of active transport, "pumps" refer to specific types of proteins embedded in the cell membrane. These proteins are responsible for facilitating the movement of molecules against their concentration gradient.

3. **Energy Requirement**: The process of active transport requires energy, typically in the form of ATP (adenosine triphosphate). This energy is necessary because moving substances against their natural flow (from low to high concentration) is energetically unfavorable.

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