Diffusion: it is the net movement of molecules from region of higher concentration to region of lower concentration. It is random e.g diffusion of water in the plant. Bulk flow:Particle moves from area of high pressure to low pressure across far distance .It is non random Bulk flow occur in gas exchange in lungs .Respiration involves movement of oxygen across membrane by diffusion Solution Diffusion: it is the net movement of molecules from region of higher concentration to region of lower concentration. It is random e.g diffusion of water in the plant. Bulk flow:Particle moves from area of high pressure to low pressure across far distance .It is non random Bulk flow occur in gas exchange in lungs .Respiration involves movement of oxygen across membrane by diffusion.