The digestive system breaks down food into:

Answer Explanation

d. all of the above

- Correct: All of the statements are true regarding the stomach:

a. muscles churn and mix the food with acids and enzymes: The stomach has muscular walls that contract and relax to mechanically churn and mix food with gastric juices, including hydrochloric acid and various enzymes (such as pepsin) that aid in the digestion of proteins.

b. glands make 3 quarts of digestive juices each day: The gastric glands in the lining of the stomach produce gastric juice, which contains hydrochloric acid, enzymes (such as pepsinogen), mucus, and intrinsic factor. These glands collectively secrete about 2 to 3 liters (quarts) of gastric juice per day.

c. food leaves as a thick liquid called chyme: After mixing with gastric juices and undergoing partial digestion in the stomach, food is transformed into a semi-liquid mixture called chyme. Chyme is then gradually released from the stomach into the small intestine for further digestion and absorption.

Therefore, all of the statements accurately describe processes that occur in the stomach.

Answer Explanation

a) mouth

- Correct: The chemical digestion of starch begins in the mouth. Salivary amylase, an enzyme secreted by the salivary glands, initiates the breakdown of starch molecules into maltose and other smaller carbohydrate molecules. This process begins as soon as food enters the mouth and continues as it is mixed with saliva during chewing and swallowing.

b) esophagus

- Incorrect: The esophagus is not directly involved in the chemical digestion of starch. It serves primarily as a conduit for the passage of food from the mouth to the stomach via peristaltic contractions.

c) stomach

- Incorrect: While some minor digestion may occur in the stomach due to the presence of salivary amylase from swallowed saliva, the stomach is not the primary site of starch digestion. Its acidic environment inhibits the activity of salivary amylase, so significant starch digestion does not occur there.

d) small intestine

- Incorrect: Starch digestion continues in the small intestine, primarily in the duodenum, but it does not begin there. Enzymes such as pancreatic amylase and brush border enzymes further break down starch into simpler sugars in the small intestine.

Answer Explanation

b) trypsin

- Correct: Trypsin is an enzyme involved in the chemical digestion of protein. It is secreted as trypsinogen by the pancreas and activated to its active form, trypsin, by enterokinase in the duodenum. Trypsin breaks down proteins into smaller peptides by cleaving peptide bonds between specific amino acids.

a) pancreatic amylase

- Incorrect: Pancreatic amylase is an enzyme involved in the digestion of carbohydrates (starches). It breaks down starch molecules into maltose and other simpler sugars.

c) sucrase

- Incorrect: Sucrase is an enzyme involved in the digestion of disaccharide sugars, specifically sucrose. It catalyzes the hydrolysis of sucrose into its constituent monosaccharides, glucose, and fructose.

d) pancreatic nuclease

- Incorrect: Pancreatic nuclease is an enzyme involved in the digestion of nucleic acids (DNA and RNA). It breaks down nucleic acid molecules into their component nucleotides.