Answer: The correct answer is: C. acid-producing enzymes in the lysosomal lumen.
Step-by-step explanation:
1. Lysosomes: Lysosomes are membrane-bound organelles found within cells. They contain a variety of enzymes called acid hydrolases that function optimally at an acidic pH.
2. pH difference: The pH of the lysosomes is lower (more acidic) compared to the cytosol. This acidic environment is essential for the proper functioning of the lysosomal enzymes.
3. Acid-producing enzymes: Lysosomes contain acid-producing enzymes, such as proton pumps, which actively transport protons (H+) into the lysosomal lumen. These enzymes contribute to the acidification of the lysosome.
4. Action of enzymes: Once the lysosomal enzymes are inside the lysosomal lumen, they can break down various biomolecules, including proteins, lipids, carbohydrates, and nucleic acids. The acidic pH is necessary for the optimal activity of these enzymes.
Option A, Na+ and OH− transport proteins in the lysosomal membrane, is incorrect because lysosomes do not actively transport Na+ and OH− ions.
Option B, H+ and Cl− transport proteins in the plasma membrane, is also incorrect. While H+ and Cl− ions are involved in maintaining the acidic environment in lysosomes, they are transported by specific proteins in the lysosomal membrane, not the plasma membrane.
Option D, H+ and Cl− transport proteins in the lysosomal membrane, is incorrect because although H+ and Cl− ions are involved in maintaining the acidity of the lysosomes, they are transported by specific proteins in the lysosomal membrane, not solely responsible for the lower pH.
In summary, the pH of lysosomes is lower than that of the cytosol because of the action of acid-producing enzymes in the lysosomal lumen. These enzymes actively transport protons (H+) into the lysosomal lumen, creating an acidic environment necessary for their optimal activity.