Diffusion is the moving of solutes from a region of higher solute concentration to a region of low solute concentration. It does not require energy so we say it is a “passive process” and it can occur it all phases i.e. solid, gas and liquid. A everyday-life example that can illustrate the process of diffusion is the entering of oxygen into our bloodstream. After we breath oxygen in, the oxygen has to find a way to enter our bloodstream. In very simple words, the oxygen will passively enter the bloodstream in the blood capillaries because the bloodstream will be deoxygenated (low oxygen concentration), while the oxygen in the alveoli(where the oxygen will come from) is higher. The same happens with Carbon dioxide but towards the opposite direction since we want to get rid of it.