Which of these is involved in the chemical digestion of protein?

Correct Answer: B

Rationale: The correct answer is B: trypsin. Trypsin is an enzyme produced by the pancreas that specifically breaks down proteins into smaller peptides. It works in the small intestine to continue the process of protein digestion. Pancreatic amylase (A) breaks down carbohydrates, sucrase (C) breaks down sucrose, and pancreatic nuclease (D) breaks down nucleic acids, not proteins. Therefore, trypsin is the only enzyme involved in the chemical digestion of protein among the choices provided.

Correct Answer: C

Rationale: The majority of carbohydrate digestion occurs in the mouth. This is because the enzyme amylase, present in saliva, begins breaking down carbohydrates into simpler sugars like maltose. The process starts in the mouth as the food is chewed and mixed with saliva, creating a bolus that can be easily swallowed. In the stomach, the acidic environment actually inhibits amylase activity, so minimal carbohydrate digestion occurs there. The small intestine is where further digestion and absorption of carbohydrates primarily happen, but the initial breakdown in the mouth is crucial. The esophagus is not involved in digestion, but rather in the transportation of food to the stomach.

Correct Answer: A

Rationale: The correct answer is A, the small intestine, because it is the primary site for nutrient absorption in the digestive system. The small intestine is lined with villi and microvilli, increasing its surface area for efficient absorption. It contains specialized cells that transport nutrients into the bloodstream for distribution to the body. The stomach (B) primarily breaks down food using digestive enzymes and acids, while the pancreas (C) secretes digestive enzymes but does not directly absorb nutrients. The liver (D) plays a role in bile production and detoxification, but nutrient absorption occurs mainly in the small intestine.

Correct Answer: B

Rationale: The correct answer is B: Chemical digestion of proteins. The stomach produces hydrochloric acid and enzymes like pepsin to break down proteins into peptides and amino acids. This process is essential for protein digestion. Mechanical digestion (A) occurs mainly in the mouth and intestines. Absorption of nutrients (C) primarily takes place in the small intestine. Neutralization of stomach acid (D) is not the primary role of the stomach; rather, the stomach maintains an acidic environment for digestion.

Correct Answer: C

Rationale: The correct answer is C because the pharyngeal phase of swallowing involves the peristaltic activity of the upper third of the esophagus, pushing the food bolus towards the stomach. This phase is involuntary and is controlled by the swallowing reflex. Choices A, B, and D are incorrect because the pharyngeal phase is entirely involuntary, the upper esophageal sphincter opens during the esophageal phase, and the opening of the glottis is associated with protection of the airway during swallowing, not the pharyngeal phase.