In biochemistry, pH is a measure of the hydrogen ion (H+) concentration of a solution. It is used to determine the acidity or alkalinity of a substance. In chemistry, it is the negative logarithm of hydrogen ion concentration expressed in molarity. On a scale of 0 to 14, a pH o 7 represents neutrality. pH level that is below 7 indicates acidity whereas pH level above 7 indicates alkalinity.
In biology, pH is an essential factor influencing the metabolic activities of a cell, a tissue, or an organism. The pH of different cellular compartments, body fluids, and organs is usually tightly regulated in a process called acid-base homeostasis. Lysosomes have a pH level of 4.5. Cytosol has a neutral pH, i.e. 7.2. The mitochondrial matrix has a pH of 7.5. The human gastric acid has pH ranging from 1.5 to 3.5. Human skin has a pH of 4.7. Urine has a pH o 6.0. Blood has a pH between 7.34 and 7.45. Pancreatic secretions have a pH o 8.1.
In microbiology, pH is an essential factor in the growth and survival of microorganisms. Microorganisms that prefer an acidic environment are called acidophiles whereas those that prefer an alkaline environment are called alkaliphiles. And, microorganisms that thrive in a neutral environment, i.e. neither acidic nor alkaline, are called neutrophiles.