Carbohydrates I Practice Quiz (13 questions)

1. Regarding carbohydrate classification by monosaccharide-unit count:

A. Polysaccharides contain more than ten monosaccharide units.

B. A monosaccharide contains one monosaccharide unit, whereas a disaccharide contains two.

C. Sugar alcohols are classified as derived carbohydrates.

D. Carbohydrates are classified into these groups according to their monosaccharide-unit count.

E. Oligosaccharides contain three to ten monosaccharide units.

Answer: (A), (B), (C), (D), (E)

Explanation

A monosaccharide has one unit, a disaccharide has two, and oligosaccharides have three to ten. Polysaccharides have more than ten units, and sugar alcohols are derived carbohydrates; the classification is based on unit count.

2. Which statements describe the distinction between simple and complex carbohydrates?

A. A carbohydrate with three units belongs to the simple-carbohydrate category.

B. Simple carbohydrates contain one or two monosaccharide units.

C. Complex carbohydrates contain three or more monosaccharide units.

D. A disaccharide belongs to the simple-carbohydrate category.

E. Polyols are derived from simple sugars.

Answer: (B), (C), (D), (E)

Explanation

Simple carbohydrates have one or two monosaccharide units, while complex carbohydrates have three or more; polyols derive from simple sugars. A disaccharide is therefore simple, whereas a three-unit carbohydrate is complex.

3. Monosaccharides grouped by carbon count include:

A. A pentose contains six carbon atoms.

B. A triose contains three carbon atoms.

C. A pentose contains five carbon atoms.

D. A tetrose contains four carbon atoms.

E. A hexose contains six carbon atoms.

Answer: (B), (C), (D), (E)

Explanation

The names correspond to three, four, five, and six carbons for trioses, tetroses, pentoses, and hexoses, respectively. A six-carbon monosaccharide is a hexose, not a pentose.

4. Which statements correctly distinguish aldoses from ketoses?

A. Galactose contains a ketone group and is classified as a ketose.

B. Aldoses contain ketone groups, whereas ketoses contain aldehyde groups.

C. Glucose contains an aldehyde group and is classified as an aldose.

D. Glucose contains a ketone group and is classified as a ketose.

E. Fructose contains an aldehyde group and is classified as a ketose.

Answer: (C)

Explanation

Glucose and galactose contain aldehyde groups and are classified as aldoses. Fructose contains a ketone group and is classified as a ketose, not as a sugar with an aldehyde group.

5. Which monosaccharide isomers are identified as biologically significant in human metabolism?

A. α-D-galactose is identified as biologically significant in human metabolism.

B. β-D-glucose is identified as biologically significant in human metabolism.

C. α-D-glucose is identified as biologically significant in human metabolism.

D. α-D-fructose is identified as biologically significant in human metabolism.

E. β-D-fructose is identified as biologically significant in human metabolism.

Answer: (A), (C), (E)

Explanation

The identified biologically significant isomers are α-D-glucose, β-D-fructose, and α-D-galactose. The β-D-glucose and α-D-fructose forms are not the isomers specified.

6. Regarding glucose as a dietary monosaccharide:

A. Glucose is also called levulose and is the sweetest monosaccharide.

B. Glucose has the molecular formula C₆H₁₂O₆ and is a monosaccharide.

C. Glucose is also called grape sugar or blood sugar.

D. Glucose crystallizes less readily than sucrose and fructose.

E. Glucose is the body's primary energy source.

Answer: (B), (C)

Explanation

Glucose is a monosaccharide with formula C₆H₁₂O₆, is also called grape sugar or blood sugar, and serves as the body's primary energy source. Levulose is another name for fructose, which is the sweetest monosaccharide and crystallizes less readily than glucose or sucrose.

7. Which statements describe glucose dependence in the brain and mature erythrocytes?

A. The brain uses glucose as its energy source.

B. Mature erythrocytes use glucose as their energy source.

C. The brain and mature erythrocytes depend exclusively on glucose for energy.

D. Other cells are not stated to share the same exclusive glucose dependence.

E. Severe hypoglycemia can cause serious damage to the brain.

Answer: (A), (B), (C), (D), (E)

Explanation

The brain and mature erythrocytes use only glucose as an energy source, and severe hypoglycemia can seriously damage the brain. The stated exclusive dependence applies to those two cell types; it is not extended to other cells.

8. Which statements about oxidation at carbon 6 of a hexose are correct?

A. Oxidation at carbon 6 of glucose can form glucuronic acid.

B. Oxidation at carbon 6 of glucose can support vitamin D synthesis.

C. Carbon 6 oxidation converts a hexose's –CH₂OH group into –COOH.

D. Carbon 6 oxidation of glucose contributes to collagen synthesis.

E. Carbon 6 oxidation of glucose contributes to glycogen synthesis.

Answer: (A), (C)

Explanation

Oxidation changes the C-6 –CH₂OH group into –COOH, forming a uronic acid; glucose can yield glucuronic acid. The uronic acid pathway contributes to vitamin C synthesis, detoxification and glycosaminoglycan synthesis, rather than vitamin D, collagen or glycogen synthesis.

9. Which statements distinguish invert sugar from sucrose?

A. Invert sugar contains free monosaccharides, unlike bonded sucrose.

B. Invert sugar is a 1:1 mixture of free glucose and fructose.

C. Invert sugar is a 1:1 mixture of free glucose and galactose.

D. Sucrose contains glucose and fructose chemically joined as a disaccharide.

E. Sucrose is a 1:1 mixture of free glucose and fructose.

Answer: (A), (B), (D)

Explanation

Invert sugar consists of free glucose and fructose in a 1:1 mixture, while sucrose chemically bonds those sugars as a disaccharide. Replacing fructose with galactose or describing sucrose as a free mixture gives the wrong composition or structure.

10. Regarding the structure of lactose:

A. Lactose makes up 4–5% of human milk.

B. Lactose is the main carbohydrate found in milk.

C. Lactose joins glucose and fructose through a β-1,4 glycosidic bond.

D. Lactose makes up 7–8% of cow's milk.

E. Lactose joins glucose and galactose through a β-1,4 glycosidic bond.

Answer: (B), (E)

Explanation

Lactose is the main carbohydrate of milk and consists of glucose and galactose joined by a β-1,4 bond. Human milk contains 7–8% lactose, while cow's milk contains 4–5%; lactose does not join glucose and fructose.

11. When insufficient lactase leaves lactose undigested, what happens?

A. Fermentation of undigested lactose can lead to bloating and abdominal pain.

B. Bacteria ferment undigested lactose in the large intestine, producing gas and organic acids.

C. Undigested lactose passes into the stomach, where bacteria produce gas.

D. Undigested lactose passes from the small intestine into the large intestine.

E. Lactose fermentation can lead to diarrhea and flatulence.

Answer: (A), (B), (D), (E)

Explanation

Insufficient lactase allows lactose to reach the large intestine, where bacteria ferment it into gas and organic acids. The resulting symptoms can include bloating, abdominal pain, diarrhea, and flatulence; the stomach is not the stated site.

12. Which statement describes a cause of lactose intolerance?

A. Secondary lactose intolerance results from complete lactase absence from birth.

B. Primary lactose intolerance results from intestinal mucosal injury.

C. Secondary lactose intolerance results from genetically programmed lactase decline after weaning.

D. Congenital lactose intolerance results from a decline in lactase after weaning.

E. Congenital lactose intolerance results from complete lactase absence from birth.

Answer: (E)

Explanation

Congenital lactose intolerance is caused by complete absence of lactase from birth. Primary intolerance involves a genetically programmed decline after weaning, whereas secondary intolerance follows intestinal mucosal injury.

13. During intestinal carbohydrate digestion and absorption, which statements are accurate?

A. Brush-border enzymes hydrolyze disaccharides at specific bonds, and glucose enters by active transport.

B. Glucose and fructose enter by active transport, while galactose uses facilitated diffusion.

C. Fructose enters by facilitated diffusion, and absorbed monosaccharides travel first to the pancreas.

D. Galactose enters by facilitated diffusion, and absorbed monosaccharides travel first to the kidneys.

E. Brush-border enzymes hydrolyze disaccharides at specific bonds, and fructose enters by passive diffusion.

Answer: (A)

Explanation

Brush-border enzymes hydrolyze disaccharides at specific bonds, and glucose uses active transport. Galactose also uses active transport, whereas fructose uses facilitated diffusion; all three monosaccharides enter the blood and travel to the liver.