What is the combined effect of concentration gradient and membrane potential on ion movement called?

The combined effect of the concentration gradient and membrane potential on ion movement is termed the electrochemical gradient. This gradient considers both the concentration of ions across the membrane and the electrical potential difference, influencing the direction and rate at which ions move across a membrane.

The concentration gradient refers to the difference in the concentration of a substance across a membrane, encouraging ions to move from an area of high concentration to one of lower concentration. Meanwhile, the membrane potential, or electric potential difference, constitutes the voltage difference across the membrane, which affects how ions, charged particles, will be attracted or repelled based on their charge.

Together, these two forces determine the net movement of ions, allowing for the proper functioning of cells, particularly in processes like nerve impulse transmission and muscle contraction. As a result, the electrochemical gradient is a crucial concept in understanding how ions behave in biological systems. The other options do not encompass both aspects of concentration and electrical potential in their definitions, which is why they are not the correct answer.