Final answer:
The stomach contains the H/K-ATPase-type pump, which secretes concentrated acid into the stomach chamber. This acid is necessary for protein digestion in the stomach.
Step-by-step explanation:
The stomach contains the H/K-ATPase-type pump, which secretes concentrated acid (up to 0.16 N HCl) into the stomach chamber. This acid is secreted by parietal cells, which combine hydrogen and chloride ions to form hydrochloric acid. This highly acidic environment is necessary for protein digestion in the stomach, as it helps activate the enzyme pepsin that breaks down proteins into smaller polypeptides.