What is rate of change of position at a specific point in time?

instantaneous speed. the rate of change in position at a given point in time. velocity. the speed of an object and the direction of its motion.

so whats the answer

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.