AQA GCSE Biology Paper 1 2025 – 400 Free Practice Questions to Pass the Exam

Hydrochloric acid in the stomach plays a crucial role in digestion by fulfilling multiple functions. It helps to create an acidic environment, which is necessary for the optimal activity of digestive enzymes, particularly pepsinogen, which is converted to pepsin in the presence of acid. Pepsin, in turn, is essential for the breakdown of proteins into smaller peptides.

Moreover, the low pH achieved by hydrochloric acid also serves to kill harmful bacteria that may enter the stomach with food, thus providing a protective barrier against infections. This acid environment is vital for the proper function of digestive enzymes and for ensuring that pathogens are eliminated, making the statement about its role in killing bacteria and creating an optimal pH for enzymes accurate.

The other choices do not correctly represent the primary functions of hydrochloric acid in the stomach. For instance, hydrochloric acid does not aid in digesting cellulose, neutralizing bile, or increasing nutrient absorption in the intestines. Rather, it primarily assists in preparing food for further digestion and in protecting the body from potential pathogens.