Digestive System

What are reasonable estimates of the optimal pH values for pepsin and chymotrypsin, respectively? A. 1.5, 6.5 B. 1.5, 12 C. 6.5, 2 D. 7.4, 7.4

A. 1.5, 6.5 Hide Explanation The stomach is a highly acidic environment, where HCl causes the pH to drop below 2. Any enzymes that operate here, including pepsin, must be able to function efficiently in such conditions. In contrast, chymotrypsin operates within the small intestine, where the pH is higher due to the secretion of bicarbonate ion. B. 1.5, 12 Hide Explanation A pH of 12 is too high of an estimate for the environment of the small intestine. This value would be over one thousand times more basic than physiological pH. C. 6.5, 2 Hide Explanation This choice wrongly characterizes the small intestine, instead of the stomach, as the more acidic environment. D. 7.4, 7.4 Hide Explanation Since these two enzymes function under very different conditions, it stands to reason that their optimal pH values would differ as well.

Cholesterol is a critical biological molecule for living organisms. Which of the following is NOT a role that cholesterol plays in the body? A. A precursor to steroid hormones B. A precursor to nucleic acids C. A contributor to plasma membrane fluidity D. A precursor to bile salts

A. A precursor to steroid hormones Hide Explanation Cholesterol plays a role in maintaining membrane fluidity and is a steroid precursor. Steroids then can be converted into bile salts. Cholesterol does not play a role in nucleic acid synthesis. B. A precursor to nucleic acids Hide Explanation Cholesterol plays a role in maintaining membrane fluidity and is a steroid precursor. Steroids then can be converted into bile salts. Cholesterol does not play a role in nucleic acid synthesis. C. A contributor to plasma membrane fluidity Hide Explanation Cholesterol plays a role in maintaining membrane fluidity and is a steroid precursor. Steroids then can be converted into bile salts. Cholesterol does not play a role in nucleic acid synthesis. D. A precursor to bile salts Hide Explanation Cholesterol plays a role in maintaining membrane fluidity and is a steroid precursor. Steroids then can be converted into bile salts. Cholesterol does not play a role in nucleic acid synthesis.

Which of the following is NOT a part of the small intestine? A. Ileum B. Cecum C. Duodenum D. Jejunum

A. Ileum Hide Explanation The ileum is the final segment of the small intestine. B. Cecum Hide Explanation The cecum is part of the large intestine. C. Duodenum Hide Explanation The duodenum is the initial segment of the small intestine. D. Jejunum Hide Explanation The jejunum is the intermediate segment of the small intestine.

How is structure B transported in the bloodstream? Pic A- Triacylglycerol B- Fatty Acid C-Glycerin A. It does not travel through the blood. B. It requires carrier proteins, like lipoproteins or albumin. C. It reacts with structure B to form structure A, which can travel through the circulatory system. D. It travels freely in the blood.

A. It does not travel through the blood. Hide Explanation This answer choice is incorrect B. It requires carrier proteins, like lipoproteins or albumin. Hide Explanation B is correct. Structure B is a fatty acid, which is hydrophobic. As a result, it requires carriers for transport through the blood. C. It reacts with structure B to form structure A, which can travel through the circulatory system. Hide Explanation Triacylglycerides don't travel through the blood due to their large size. D. It travels freely in the blood. Hide Explanation This answer choice is incorrect

Starch in the digestive system is broken down by which enzyme? A. Lysozyme B. Amylase C. Pepsin D. Trypsin

A. Lysozyme Hide Explanation Lysozyme hydrolyzes β-1,4 linkages in bacterial cell walls. B. Amylase Hide Explanation B is correct. Two types of amylase exist: salivary and pancreatic. Both of these work to break down starches. C. Pepsin Hide Explanation Pepsin is a protease released into the stomach that digests protein. D. Trypsin Hide Explanation Trypsin is a pancreatic protease.

Chief cells in the stomach contain pepsinogen. Why does pepsinogen NOT damage the chief cells prior to secretion? A. Pepsinogen is a zymogen that is activated by HCl. B. Pepsinogen is not active in chief cells. C. Chief cells are immune to the effects of pepsinogen. D. Chief cells secrete bicarbonate to neutralize and inactivate the pepsinogen.

A. Pepsinogen is a zymogen that is activated by HCl. Hide Explanation The -ogen ending on an enzyme indicates that it is a zymogen, an inactive precursor form.Thus, pepsinogen cannot damage cells. Instead, its active form (pepsin) exerts proteolytic activity that could potentially damage cells. B. Pepsinogen is not active in chief cells. Hide Explanation While this is technically correct, choice A is the better explanation for why pepsinogen does not damage chief cells. C. Chief cells are immune to the effects of pepsinogen. Hide Explanation It is not that chief cells are immune to pepsinogen, but rather that pepsinogen is an inactive precursor. D. Chief cells secrete bicarbonate to neutralize and inactivate the pepsinogen. Hide Explanation Pepsinogen is already an inactive precursor. Therefore, it does not need to be neutralized or inactivated by chief cells.

Which of the following vitamins is degraded into retinal, which aids in sight? A. Vitamin A B. Vitamin C C. Vitamin E D. Vitamin K

A. Vitamin A Another name for Vitamin A is retinol.

Salivary amylase aids in the digestion of: A. lipids. B. polysaccharides. C. polypeptides. D. monosaccharides.

A. lipids. Hide Explanation Lipid digestion begins in the small intestine. B. polysaccharides. Hide Explanation Polysaccharides, such as starches are first broken up in the mouth by salivary amylase. Monosaccharides are not metabolized until glycolysis or other metabolic pathways. C. polypeptides. Hide Explanation Polypeptide digestion begins in the stomach. D. monosaccharides. Hide Explanation Monosaccharides are not metabolized until glycolysis or other metabolic pathways.

Bile, a substance used to emulsify fats and aid in their digestion, is formed in the: A. liver. B. gallbladder. C. bone marrow. D. pancreas.

A. liver. Hide Explanation Bile is formed in the liver and stored in the gallbladder. B. gallbladder. Hide Explanation While bile is stored in the gallbladder, it is not formed there. C. bone marrow. Hide Explanation Bile should not be present in the bone marrow. D. pancreas. Hide Explanation While the common bile duct does pass through the pancreas before emptying into the duodenum, bile is not formed in the pancreas.

Peristalsis may refer to the rhythmic contractions of muscle in the ______ and _______. A. mouth, large intestine B. lungs, esophagus C. small intestine, esophagus D. large intestine, kidneys

A. mouth, large intestine Hide Explanation While peristalsis does occur in the large intestine, it does not occur in the mouth. B. lungs, esophagus Hide Explanation While peristalsis does occur in the esophagus, it does not occur in the lungs. C. small intestine, esophagus Hide Explanation Peristalsis occurs in the esophagus, small intestine, and large intestine. D. large intestine, kidneys Hide Explanation While peristalsis does occur in the large intestine, it does not occur in the kidneys.

Pepsin aids in the digestion of: A. polysaccharides. B. polypeptides. C. disaccharides. D. lipids.

A. polysaccharides. Hide Explanation Pepsin breaks peptide bonds, which are not present in polysaccharides. B. polypeptides. Hide Explanation Pepsin breaks peptide bonds. C. disaccharides. Hide Explanation Pepsin breaks peptide bonds, which are not present in disaccharides. D. lipids. Hide Explanation Pepsin breaks peptide bonds, which are not present in lipids.

A physician is analyzing a particular digestive molecule, but (due to an unfortunate memory lapse) forgets which molecule he is studying. If he knows only that this molecule is not initially secreted as a zymogen, he may be dealing with: A. trypsin. B. pepsin. C. chymotrypsin. D. gastrin.

A. trypsin. Hide Explanation This enzyme is originally released as a zymogen or a proenzyme. The inactive protein product must be cleaved or otherwise modified before it can be activated. B. pepsin. Hide Explanation This enzyme is originally released as a zymogen or a proenzyme. The inactive protein product must be cleaved or otherwise modified before it can be activated. C. chymotrypsin. Hide Explanation This enzyme is originally released as a zymogen or a proenzyme. The inactive protein product must be cleaved or otherwise modified before it can be activated. D. gastrin. Hide Explanation Gastrin is secreted by G cells and promotes the release of hydrochloric acid by parietal cells in the stomach. Unlike many digestive substances, it is a hormone, not an enzyme; as such, it is not initially present in zymogen form.

Doctors measured the glucose, blood pH, and insulin levels of a patient at intake and post-treatment and found the following results. What is the reason for the low blood pH of the patient at intake?

B. Ketone body generation can promote acidosis. Hide Explanation B is correct. The patient is in a prolonged state of starvation, so his body is producing a large amount of ketones to provide fuel. If this state continues for too long, the patient may develop ketoacidosis.

According to the passage which of the following methods would be most effective for separating unconjugated bilirubin (shown below) from conjugated bilirubin?

B. Liquid-liquid extraction using water and benzene Hide Explanation As the first paragraph tells us, conjugated bilirubin (bilirubin connected to a carboxylic acid) is solubilized (i.e. made water-soluble). This is deduced from the fact that being joined with a highly polar, H-bonding molecule like glucuronic acid is what made the molecule soluble. The question also shows us the structure of free bilirubin, which is largely hydrophobic. Using water (polar) and benzene (nonpolar/organic), the conjugated form will be soluble in water while the unconjugated form will stay in the organic layer.

Chymotrypsin is an intestinal enzyme that is used to digest proteins. In the absence of food, chymotrypsin does not digest any non-target proteins because chymotrypsin:

B. is synthesized as a zymogen, which is activated by other digestive enzymes in the presence of food. Hide Explanation B is correct. You must recall that many digestive enzymes are synthesized as zymogens.

The human liver has high regenerative capacity. What does this mean?

C. It can undergo extensive, but not complete, regrowth; thus, people can donate up to 50% of their livers and will eventually experience regeneration of the missing portion. Hide Explanation Regenerative capacity refers to an organ's ability to rebuild itself. Humans exhibit partial regeneration in response to injury, with the liver representing an organ with high regenerative capacity. Thus, this structure can undergo extensive, but not complete, regrowth. In fact, a person can donate up to 50% of his liver and it will regrow the missing portion.

Fat is broken down in the digestive system by lipase and emulsified by bile, a molecule that tends to form amphipathic salts. Which correctly identifies the origins of lipase and bile?

C. Lipase is released from the pancreas, while bile is synthesized in the liver and stored in the gall bladder. Hide Explanation The lipase used to digest lipids in the small intestine is also known as pancreatic lipase, a term that denotes the organ in which it is produced. In contrast, bile is synthesized by the liver, then travels to the gall bladder, where it is stored until needed. Both lipase and bile are released into the duodenum to act.

Which of these are functions of the large intestine? I. Water absorption II. Electrolyte absorption III. Fat absorption IV. Provision of an environment for E. coli A. III only B. IV only C. III and IV D. I, II, and IV

D. I, II, and IV Hide Explanation D is correct. I, II, and IV all occur in the large intestine.

The normal flora of the large intestine consists mainly of: A. bacteria. B. fungi. C. protozoa. D. viruses.

The large intestine contains enormous numbers of bacteria, which help aid in digestion and even produce some vitamins, such as vitamin K.

With regard to digestion, it is accurate to say that: A. the liver releases bicarbonate ions into the duodenum to make it less acidic than the stomach. B. parietal cells secrete gastrin to inhibit the release of HCl. C. the pancreas releases enzymes and hydrochloric acid into the duodenum. D. pepsinogen is produced by chief cells in the stomach, then stimulated by the low pH to be cleaved into pepsin.

With regard to digestion, it is accurate to say that: A.Bicarbonate is produced by the pancreas, not the liver. B. G cells, not parietal cells, release gastrin. Additionally, gastrin promotes the secretion of hydrochloric acid. C.The pancreas does release enzymes into the duodenum, but it does not secrete HCl. In contrast, it releases bicarbonate to raise the pH of the duodenum to approximately 6. D. pepsinogen is produced by chief cells in the stomach, then stimulated by the low pH to be cleaved into pepsin. Hide Explanation Pepsinogen is a zymogen, or inactive enzyme precursor, that is released by chief cells. This prevents pepsin, a protease, from degrading stomach cells while it is stored. Once released into the stomach, the low pH denatures the pepsinogen protein and reveals cleavage points that neighboring pepsinogen molecules attack to produce pepsin.