Which of these ingredients in saliva is responsible for activating salivary amylase?

Correct Answer: B

Rationale: The correct answer is B: phosphate ions. Phosphate ions present in saliva help activate salivary amylase by providing the necessary environment for the enzyme to function optimally. Salivary amylase works best at a slightly alkaline pH, which is facilitated by the presence of phosphate ions. Mucus (choice A) primarily helps with lubrication and binding of food particles but does not activate enzymes. Chloride ions (choice C) are not directly involved in activating salivary amylase. Urea (choice D) is a waste product and not related to enzyme activation in saliva. In summary, the correct answer is B because phosphate ions create the optimal pH environment for salivary amylase activity, while the other choices are not directly involved in enzyme activation.

Correct Answer: C

Rationale: The correct answer is C: pancreas. The pancreas secretes most digestive enzymes, including amylase, lipase, and proteases, into the small intestine to aid in the digestion of carbohydrates, fats, and proteins. It plays a crucial role in breaking down food components. The stomach (choice A) secretes gastric juices but not the majority of digestive enzymes. The liver (choice B) produces bile, which aids in fat digestion, but does not secrete digestive enzymes. The small intestine (choice D) is where most digestion and absorption occur, but it does not secrete the majority of digestive enzymes.

Correct Answer: B

Rationale: The correct answer is B: chief cells. Chief cells are responsible for secreting pepsinogen in the stomach. Pepsinogen is an inactive form of pepsin, which is an enzyme that helps in protein digestion. Parietal cells secrete hydrochloric acid, not pepsinogen. Mucous neck cells secrete mucus to protect the stomach lining. Enteroendocrine cells secrete hormones like gastrin, but not pepsinogen. Therefore, the correct answer is B as chief cells are the specific cells that secrete pepsinogen in the stomach.

Correct Answer: B

Rationale: The correct answer is B: mechanical digestion. Teeth play a crucial role in breaking down food into smaller pieces through physical chewing, which is a form of mechanical digestion. This process increases the surface area of food particles, making it easier for enzymes to further break down nutrients during chemical digestion in the stomach and intestines. Choice A (chemical digestion) is incorrect because teeth do not directly participate in chemical breakdown of food. Choice C (enzymatic digestion) is incorrect as enzymes are not produced by teeth but by salivary glands and other digestive organs. Choice D (absorption) is incorrect as teeth are not involved in absorbing nutrients; absorption primarily occurs in the small intestine.

Correct Answer: C

Rationale: The correct answer is C: Digesting proteins. Pepsin is a digestive enzyme produced in the stomach that specifically breaks down proteins into smaller peptides. It works optimally in acidic environments, aiding in the digestion of proteins consumed in the diet. The other choices are incorrect because pepsin does not play a role in digesting carbohydrates (A), fats (B), or nucleic acids (D). Carbohydrates are primarily broken down by enzymes like amylase, fats by lipase, and nucleic acids by nucleases. Thus, pepsin's main function is to digest proteins in the stomach.