Correct Answer: D

Rationale: Phytochemicals are not considered a class of nutrients. While proteins, fats, and carbohydrates are essential macronutrients providing energy and structural support, phytochemicals are non-nutrient compounds found in plants that offer various health benefits but are not essential for sustaining life like the other three choices. Therefore, the correct answer is D.

Correct Answer: C

Rationale: Mechanical digestion involves physical movements that break down food in the digestive tract. Segmentation (choice B) and peristalsis (choice D), which are both movements of the muscles in the digestive tract, are examples of this type of digestion. Heat (choice A), on the other hand, is related to chemical digestion, not mechanical digestion. Therefore, choice C (Option B and D) is the correct answer as it includes both examples of mechanical digestion provided in the choices. Choices A and D are incorrect because heat (choice A) is not a mechanical digestion process, and peristalsis (choice D) is a movement that helps propel food along the digestive tract but is not directly involved in breaking down food physically.

Correct Answer: A

Rationale: The correct answer is A: 'they must be supplied by the diet.' Essential fatty acids, like omega-3 and omega-6, cannot be produced by the body and must be obtained through the diet. They are polyunsaturated fatty acids, playing vital roles in inflammation and cell membrane structure. Choice B is incorrect because essential fatty acids cannot be produced by dehydrogenation, a process of removing hydrogen. Choice C is incorrect as not all essential fatty acids are anti-inflammatory; some have pro-inflammatory roles. Choice D is incorrect because not all essential fatty acids are polyunsaturated; omega-9, for example, is a monounsaturated essential fatty acid.

Correct Answer: A

Rationale: Phosphorus is the correct answer. It is a key component of cell membranes, being part of the phospholipid bilayer that provides structure and controls the movement of substances in and out of cells. Magnesium, iron, and iodine do not serve as principal components of cell membranes. Magnesium is involved in various enzymatic reactions, iron is essential for oxygen transport, and iodine plays a role in thyroid hormone synthesis.

Correct Answer: B

Rationale: Pepsin, choice B, is the correct answer as it is a proteolytic enzyme that is essential for the breakdown of large protein molecules in the stomach. Gastric lipase, choice A, is incorrect because it primarily targets fats, not proteins, hence it is not involved in protein hydrolysis. Mucus, choice C, is incorrect as it serves to protect the stomach lining from acidic gastric juices and does not play a direct role in protein digestion. Intrinsic factor, choice D, is incorrect as it is vital for the absorption of Vitamin B12 in the small intestine and doesn't participate in the process of hydrolyzing proteins.