Which of these nutrients is absorbed mainly in the duodenum?

Answer Explanation

C) They change food substances into molecules that can pass into the bloodstream and cells.

- Correct: Digestive enzymes secreted by the pancreas play a crucial role in breaking down complex food molecules into smaller, absorbable molecules that can pass through the walls of the small intestine and into the bloodstream. These smaller molecules include carbohydrates broken down into simple sugars, proteins broken down into amino acids, and fats broken down into fatty acids and glycerol. Once these molecules are absorbed into the bloodstream, they can be transported to cells throughout the body to provide energy and support various metabolic processes.

A) They form proteins needed in the stomach.

- Incorrect: Digestive enzymes do not form proteins needed in the stomach. Proteins are broken down into amino acids by digestive enzymes, but the enzymes themselves do not form proteins.

B) They form the acids that break down food.

- Incorrect: Digestive enzymes do not form acids. Acids such as hydrochloric acid are secreted by the stomach and aid in the breakdown of food, particularly proteins, but they are not formed by pancreatic enzymes.

D) They change food materials into wastes that can be passed out of the body.

- Incorrect: While digestive enzymes help break down food materials, their primary function is to convert these materials into absorbable molecules rather than wastes. The conversion of food into waste products occurs primarily through processes in the digestive tract and is facilitated by enzymes as part of digestion, but it is not the direct role of pancreatic enzymes.

Answer Explanation

A) The stomach - This is an organ of the digestive system. It plays a crucial role in breaking down food through the secretion of gastric juices, which contain enzymes and acids to begin the process of digestion. Therefore, option A is correct.

B) The mouth - The mouth is also an organ of the digestive system. It is where the process of digestion begins, as it is responsible for chewing and breaking down food into smaller pieces. Additionally, saliva produced in the mouth contains enzymes that start the chemical breakdown of food. Therefore, option B is correct.

C) The intestines - Both the small intestine and the large intestine are essential organs of the digestive system. The small intestine is where most of the absorption of nutrients from food occurs, while the large intestine absorbs water and salts from the material that has not been digested. Therefore, option C is correct.

D) The heart - The heart is not an organ of the digestive system. Instead, it is a part of the circulatory system responsible for pumping blood throughout the body. While the circulatory system works in conjunction with the digestive system to transport nutrients absorbed from the intestines to various tissues and organs, the heart itself is not directly involved in digestion. Therefore, option D is incorrect.

Answer Explanation

Enzymes are proteins that catalyze specific biochemical reactions in living organisms.

The production of enzymes is regulated by gene expression, where specific genes are activated (expressed) to produce particular enzymes in different cells or tissues.

In this case, the gene responsible for coding the enzyme pepsin is expressed in the cells of the stomach, leading to the production of pepsin in the stomach.

Conversely, the gene for trypsin is expressed in the cells of the small intestine, resulting in the production of trypsin in the small intestine.

Therefore, the reason that the stomach and small intestine produce different enzymes is due to the differential gene expression in these respective tissues.