▶️ Answer/Explanation
(a) Chemical digestion is the breakdown of large molecules into smaller molecules or the conversion of insoluble substances into soluble ones through enzymatic reactions.
Explanation: This process involves enzymes that catalyze the hydrolysis of complex food molecules (like starch, proteins, and fats) into simpler, absorbable forms (like sugars, amino acids, and fatty acids). It occurs in the mouth, stomach, and small intestine.
(b)(i)
Explanation: Amylase breaks down starch into sugars (e.g., maltose), lipase hydrolyzes fats into fatty acids and glycerol, and protease digests proteins into amino acids.
(b)(ii)
amylase: salivary glands and pancreas
lipase: pancreas
protease: stomach (as pepsin) and pancreas
Explanation: Amylase is secreted in saliva (mouth) and pancreatic juice (small intestine). Lipase is primarily produced by the pancreas. Protease enzymes like pepsin are made in the stomach, while others (trypsin) come from the pancreas.
(c)(i) Hydrochloric acid (HCl)
Explanation: Gastric juice in the stomach contains HCl, which creates an acidic environment (pH ~2) essential for digestion and pathogen control.
(c)(ii)
1. Kills harmful microorganisms/pathogens in food, preventing infections.
2. Provides the optimum pH for pepsin (a protease) to break down proteins effectively.
Explanation: The acidic environment denatures proteins (aiding digestion) and activates pepsinogen into pepsin. It also inhibits bacterial growth, protecting the digestive system.