Cellular pH needs to be maintained close to seven because a slight shift in pH towards either acidity or alkalinity could result in serious harm to the organism, including death, coma, muscle spasms or convulsions. A slightly acidic pH of 6.95 or a more basic pH of 7.7 will inhibit the cell's ability to function properly.
The pH value of a cell's intracellular fluid is called the intracellular pH, or pHi. Close regulation of pHi is required for a cell's survival. A change in pHi can be caused by leakage of acid through organelle and plasma membranes or by metabolic acid production. Cells can regulate their pHi through the chemical actions of buffers. These are molecules that interconvert between basic and acidic forms by accepting or donating protons as needed.