The four definitions below refer to ways in which molecules and ions may pass through a cell membrane.
A the movement of water down a water potential gradient through a partially permeable membrane.
B the net movement of molecules or ions down a concentration gradient.
C movement of molecules or ions against the concentration gradient, which requires an input of energy from the cell.
D passive movement of molecules or ions across a cell membrane with the aid of transport proteins.
Name the processes A to D.
