Hydrochloric Acid (Cambridge International IGCSE Biology)

Spec point — 7.4.5 · Describe the functions of hydrochloric acid in gastric juice, limited to killing harmful microorganisms in food and providing an acidic pH for optimum enzyme activity

Hydrochloric acid

• The stomach produces several fluids which together are known as gastric juice
• One of the fluids produced is hydrochloric acid
• This kills bacteria in food and gives an acid pH for enzymes to work in the stomach

How is a low pH helpful in the stomach?

• The low pH kills bacteria in ingested food as it denatures the enzymes in their cells, meaning they cannot carry out any cell reactions to maintain life
• Pepsin, produced in the stomach, is an example of an enzyme which has a very low optimum pH - around pH 2
• The hydrochloric acid produced in the stomach ensures that conditions in the stomach remain within the optimum range for pepsin to work at its fastest rate