Where does the digestion of starch begin?

Correct Answer: C

Rationale: The correct answer is C: mouth. Starch digestion begins in the mouth with the action of salivary amylase, an enzyme that breaks down starch into maltose. This process initiates the breakdown of complex carbohydrates into simpler sugars. The stomach (A) primarily digests proteins, the small intestine (B) further breaks down carbohydrates, proteins, and fats, and the esophagus (D) is a passageway for food to travel from the mouth to the stomach. Hence, the mouth is where the digestion of starch begins due to the presence of salivary amylase.

Correct Answer: B

Rationale: The correct answer is B: stomach. The stomach is the most acidic area in the digestive tract, with a low pH due to the presence of hydrochloric acid that aids in digestion. Choice A (mouth) has a neutral pH, not as low as the stomach. Choices C (large intestine) and D (small intestine) have higher pH levels due to the neutralization of acids from previous stages. Therefore, the reading labelled X, which is at a low pH, is most likely obtained from the stomach.

Correct Answer: C

Rationale: The correct answer is C: stomach. After food leaves the esophagus, it enters the stomach for further digestion. The stomach secretes digestive enzymes and acids to break down food. The liver (choice A) is not where food enters after the esophagus. The pharynx (choice B) is part of the throat and not a digestive organ. The pancreas (choice D) is involved in producing digestive enzymes but food does not enter it directly after the esophagus.

Correct Answer: D

Rationale: The correct answer is D: the heart. The heart is not an organ of the digestive system. The digestive system is responsible for breaking down food and absorbing nutrients. The stomach, mouth, and intestines are all essential organs involved in this process. The heart, on the other hand, is part of the circulatory system, responsible for pumping blood throughout the body. It plays no direct role in digestion. Therefore, D is the correct answer.

Correct Answer: C

Rationale: The correct answer is C: converting glycogen into glucose. When no carbohydrate ingestion occurs, the liver breaks down stored glycogen into glucose through a process called glycogenolysis to maintain blood glucose levels. This process provides a source of energy for the body. Emulsification (A) is the breakdown of fats into smaller droplets, not related to carbohydrate breakdown. Manufacturing more bile (B) is not directly related to liver activity in response to no carbohydrate ingestion. Releasing iron (D) is unrelated to the liver's response to carbohydrate deprivation.