Question

what is the main responsibility of protein pumps attached to the cell membrane?
moving molecules against their concentration gradient
extra support for the cell exterior
keeping cell turgidity at normal levels

Explanation:

Protein pumps in the cell membrane are involved in active transport. Active transport requires energy (ATP) to move molecules across the membrane against their concentration gradient (from low to high concentration). The "extra support for the cell exterior" is not a function of protein pumps (structural support is more related to components like the cell wall or extracellular matrix). "Keeping cell turgidity at normal levels" is related to osmosis and the cell's water balance, not protein pumps. So the correct function is moving molecules against their concentration gradient.

Answer:

moving molecules against their concentration gradient