Correct Option: C. Protein into peptones Detailed Explanation: What is Pepsin? Pepsin is a digestive enzyme that is primarily found in the stomach. It is secreted by the stomach lining in an inactive form called pepsinogen. When pepsinogen comes into contact with the acidic environment of the stomach (due to hydrochloric acid), it is activated into pepsin. Function of Pepsin: Pepsin's main role is to break down proteins into smaller peptides, specifically into substances known as peptones. Peptones are intermediate products of protein digestion that are further broken down into amino acids by other enzymes in the small intestine. Why Option C is Correct: - Specificity of Pepsin: Pepsin specifically targets peptide bonds in proteins, which are the bonds that link amino acids together. By cleaving these bonds, pepsin effectively reduces complex proteins into smaller chains of amino acids (peptides), which are then referred to as peptones. - Digestive Process: The digestion of proteins begins in the stomach, where pepsin operates optimally at a low pH (around 1.5 to 2.0). This acidic environment is crucial for pepsin's activity and distinguishes it from other digestive enzymes that work in the more neutral pH of the small intestine. Why the Other Options are Incorrect: Option A: Cellulose into glucose molecules - Incorrect Enzyme: Cellulose is a polysaccharide made up of glucose units linked by β-1,4-glycosidic bonds. The enzyme responsible for breaking down cellulose is cellulase, not pepsin. Humans do not produce cellulase, which is why we cannot digest cellulose effectively. - Functionality: Pepsin does not act on carbohydrates, and thus cannot convert cellulose into glucose. Option B: Carbohydrates into simple sugars - Incorrect Enzyme: The digestion of carbohydrates is primarily carried out by enzymes such as amylase (found in saliva and pancreatic juice) and maltase, which break down starches and sugars into simple sugars like glucose. Pepsin does not have any role in carbohydrate digestion. - Specificity: Pepsin is specific to proteins and does not act on carbohydrates. Option D: Fats into glycerol and fatty acids - Incorrect Enzyme: The digestion of fats (lipids) is primarily facilitated by lipases, which break down triglycerides into glycerol and free fatty acids. Pepsin does not act on fats, making this option incorrect. - Digestive Process: Lipid digestion begins in the stomach with gastric lipase, but pepsin is not involved in this process. Summary:

• Pepsin is a digestive enzyme that breaks down proteins into smaller peptides called peptones.
• It is activated in the acidic environment of the stomach and works specifically on peptide bonds.
• Other options (A, B, D) involve different types of enzymes that are not related to pepsin's function.
• Understanding the specificity of digestive enzymes is crucial for grasping how the digestive system processes different macromolecules.