Which cell process will move substances against a concentration gradient?

a. active transport
b. osmosis
c. diffusion
d. facilitated diffusion

Option A) Active transport.

Explanation: Active transport - Movement of molecules or ions from a lower concentration to a region of higher concentration(against a concentration gradient), by the use of enzymes and consuming energy(ATP), hence the substances move across plasma membrane against a concentration gradient. Osmosis is the process in which molecules of the solvent passes through a semipermeable membrane(plasma membrane in case of cell) from a less concentrated solution to more concentrated one along the concentrated gradient. Energy is not required in this process and hence it is passive process. Diffusion is the movement of the molecules of a material from higher concentration to lower concentration.Facilitated diffusion is similar to diffusion, it the transport of substances across a biological membrane from an area of higher concentration to an area of lower concentration by the help of a carrier molecule.

Result: Active transport happens against a concentration gradient.

The correct answer is  b)