AP BIOLOGY

Detailed explanation-1: -area with lower concentration. The difference between the concentrations is called the “concentration gradient”. Diffusion goes down the gradient until an equilibrium is reached.

Detailed explanation-2: -Therefore, the sodium-potassium pump is an electrogenic pump (a pump that creates a charge imbalance) contributing to the membrane potential. What will happen to the opening of the sodium-potassium pump if no ATP is present in a cell? It will remain facing the extracellular space, with sodium ions bound.

Detailed explanation-3: -Secondary active transport (cotransport), on the other hand, uses an electrochemical gradient – generated by active transport – as an energy source to move molecules against their gradient, and thus does not directly require a chemical source of energy such as ATP.

Detailed explanation-4: -Passive transport, most commonly by diffusion, occurs along a concentration gradient from high to low concentration. No energy is necessary for this mode of transport.