Question

up to 25% of a cells atp is used to run sodium - potassium pumps which transport sodium outside of the cell against its concentration gradient and potassium inside the cell against its concentration gradient. without the resulting sodium and potassium gradients, neurons and muscles cannot function properly. the sodium - potassium pump is an example of

• osmosis.
• facilitated diffusion.
• diffusion.
• equilibrium.
• active transport.

Explanation:

To solve this, we analyze each option:

• Osmosis: Movement of water across a semipermeable membrane, not relevant here.
• Facilitated diffusion: Passive transport (no energy) through a protein, moves with concentration gradient.
• Diffusion: Passive movement of particles with concentration gradient, no energy.
• Equilibrium: State of balance, not a transport mechanism.
• Active transport: Requires energy (like ATP) and moves substances against concentration gradient. The sodium - potassium pump uses ATP and moves ions against their gradients, so it's active transport.

Answer:

E. active transport.