Understanding Other Digestive Physiology - AP Biology

In order to answer this question, visualize the macromolecules as their monomers. The chemical formula for ammonia is , so the monomer will need to include nitrogen. Carbohydrates are chains of monosaccharides and are only composed of carbon, hydrogen, and oxygen. Fatty acids are nonpolar molecules, and are composed of only carbon and hydrogen. Proteins are composed of amino acid monomers. Amino acids have an amino terminus, which includes a nitrogen atom. As a result, only proteins have the nitrogen atom which can be used in the byproduct of ammonia.

The liver is a very important organ with many interrelated functions, however, the liver is not responsible for the creation of antibodies. This is done by plasma cells, a key cell type in the immune system.

Glycogen is stored primarily in cells of the liver and muscles. The pancreas is responsible for secreting hydrolytic enzymes into the small intestine via the pancreatic duct. Along with these digestive enzymes the pancreas releases bicarbonate, which reacts in an acid-base reaction with acidic stomach chyme to pervent it from damaging the intestine. The pancreas also releases insulin and glucagon, among other hormones.

Secretin is a hormone released by the duodenum in response to an influx of acid. The hormone targets the stomach, to reduce the amount of acid that can pass through to the small intestine, and the pancreas, to increase secretion of bicarbonate, which neutralizes the acidity.

Cholecystokini (CCK) targets the stomach to inhibit motility, while gastrin targets the stomach to increase motility. Gastrin is secreted by the duodenum and the stomach, but targets only the stomach. CCK, however, targets the stomach, pancreas, and gall bladder.

Lipase is synthesized and secreted from the pancreas into the duodenum of the small intestine. Lipase plays a key role in the digestion of lipids.

Pepsin is the only enzyme out of the given choices that functions in the stomach, where the pH is very low (acidic). Trypsin, carboxypeptidase, and lipase all function within the small intestine, where the pH is usually more basic to neutralize the pH of chyme as food is digested. Amylase is found in saliva and functions in the mouth, where pH is about neutral.

The liver has a large number of functions, including metabolizing toxins, synthesizing proteins, and storing glucose in the form of glycogen. The only answer choice that describes liver functions is the production of bile, triglycerides, and cholesterol.

The pancreas produces insulin from beta cells, the gall bladder stores bile, and the adrenal medulla secretes epinephrine and norepinephrine. Physical digestion takes place mainly in the mouth and stomach, not the liver.

Carbohydrates begin their digestion in the mouth, where salivary amylase is produced.

Fats are emulsified by bile and digested by lipase in the small intestine. Nucleic acids are also digested in the small intestine by nucleases. Proteins begin their digestion in the stomach, where the low pH of gastric juice begins the breakdown process and pepsin begins to cleave peptide bonds. Protein digestion continues in the small intestine with other protease enzymes.

Amylase breaks down starch in the mouth and small intestine. Proteases are found in the stomach and small intestine. Water absorption occurs in the intestines (mostly the large intestine). Lipases break down lipids; fats are a type of lipid.

Complete digestion takes place in the small intestine, but pepsin is present in the stomach where it breaks down proteins to peptides. The pH in the stomach is very low, and pepsin, like all enzymes, has an optimal temperature and pH at which it functions best. For pepsin, this pH happens to be very low. The other enzymes mentioned that function in the small intestine have optimal pH's close to the pH of the small intestine (which is slightly alkaline due to the pancreas secreting bicarbonate).

Amylase is the enzyme that breaks down starches and carbohydrates. There are two types, salivary amylase and pancreatic amylase. Salivary amylase is produced in the mouth by the salivary glands and it is one of the first enzymes that begins the process of food digestion.

The correct answer is carbohydrates because amylase is the enzyme that is able to break these macromolecules down into smaller parts. There are two kinds of amylase found in the body, salivary amylase in the mouth and pancreatic amylase in the pancreas. Both of these are involved in the breakdown of carbohydrates in digestion.

The pancreas is responsible for secreting proteolytic zymogens, such as trypsinogen, into the small intestine. This is triggered by the presence of undigested food (chyme) in the duodenum.

Bile is synthesized in the liver and secreted by the gallbladder into the small intestine upon the appearance of acidic chyme in the duodenum. Bile contains salts that emulsify (solubilize) fats, which is a necessary step in their digestion. If the gallbladder is removed, the liver can take over both roles.

Salivary amylase in the mouth targets large starch molecules and begins the digestion process to a monosaccharide (i.e. glucose). Salivary amylase secretion is stimulated by the recognition of starch on sweet taste receptors, and is carried out by the salivary glands (parotid, submandibular, and sublingual).

Zymogens are inactive forms of enzymes that are secreted in order to prevent the accidental digestion of the body's important proteins (i.e. other enzymes, structural proteins). These zymogens are then activated through further processing in the compartments in which they are meant to work.

Trypsin and chymotrypsin belong to a family of enzymes that are "proteolytic". This means that they target proteins and break them down into their building blocks called amino acids.

Gastrin is secreted in the stomach, and stimulates the secretion of hydrochloric acid by parietal cells. The other three enzymes directly aid in the digestion of proteins. Trypsin and chymotrypsin are released from the pancreas into the duodenum, and pepsin digests proteins located in the stomach. Each of these has different cleavange targets within protein sequences and can be used as a restriction enzyme in experimental procedures.