A transport which is carried out by membrane prote ins and uses energy to pump molecules against a concentration gradients is

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about a type of transport that involves membrane proteins and requires energy to move molecules against a concentration gradient.

2. **Membrane Proteins**: Recognize that transport across membranes often involves specific proteins embedded in the membrane. These proteins can facilitate the movement of substances in and out of the cell.

3. **Energy Requirement**: Note that the transport in question requires energy. This is a key characteristic that differentiates it from passive transport, which does not require energy.

4. **Concentration Gradient**: Understand that a concentration gradient refers to the difference in concentration of a substance across a membrane. Molecules typically move from an area of higher concentration to an area of lower concentration (down the gradient).

5. **Against the Gradient**: The question specifies that the transport is against the concentration gradient. This means that the molecules are being moved from an area of lower concentration to an area of higher concentration.

6. **Active Transport**: The type of transport that fits all these criteria—membrane proteins, energy usage, and movement against a concentration gradient—is known as "active transport."

7. **Conclusion**: Therefore, the answer to the question is "active transport."

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