Why is diffusion important to a living cell?
Diffusion allows the exchange of substances; the entry of oxygen, proteins, etc into the cell and the removal of waste substances. A high concentration of a particular waste product may hinder the normal functioning of the cell. There may be a higher concentration of H+ ions when the CO2 concentration is high. The pH may thus become unfavourable for certain cellular processes to occur. These may be essential processes that are required to sustain the cell. Also, waste products like urea formed from the deamination of amino acids can be toxic to the cell.
