Q: Cellulose and starch are both composed of repeating glucose units. Why is cellulose difficult for most adult humans to digest, while starch is not?

Cellulose contains $eta$-1,4-glycosidic linkages, which human digestive enzymes cannot break, while starch contains $ ext{α}$-1,4-glycosidic linkages that can be hydrolyzed by human enzymes.

Question 1

Cellulose and starch are both composed of repeating glucose units. Why is cellulose difficult for most adult humans to digest, while starch is not?

Accepted Answer

Cellulose contains $eta$-1,4-glycosidic linkages, which human digestive enzymes cannot break, while starch contains $	ext{α}$-1,4-glycosidic linkages that can be hydrolyzed by human enzymes.

Question 2

Which of the following best explains why burning sugar releases energy?

Accepted Answer

The chemical bonds in carbohydrates store potential energy, which is released as heat and light when the bonds are broken during combustion.

Question 3

Which structural feature distinguishes glucose from fructose?

Accepted Answer

Glucose has an aldehyde group at the end of its carbon chain, while fructose has a ketone group in the middle of its carbon chain.

Question 4

Which of the following is a correct general formula for a monosaccharide?

Accepted Answer

$	ext{(CH}_2	ext{O)}_n$

Question 5

Amylopectin and glycogen are both storage polysaccharides. Which statement best describes a key difference between them?

Accepted Answer

Glycogen has branches that occur about once every 10 monomers, while amylopectin branches about once every 30 monomers.

Question 6

Which type of glycosidic linkage is found in cellulose, and what is its structural consequence?

Accepted Answer

$\beta$-1,4-glycosidic linkages; they generate linear molecules that allow hydrogen bonding between parallel strands.

Question 7

Which of the following best describes the role of carbohydrates in cell identity?

Accepted Answer

Carbohydrate components of glycoproteins on cell surfaces are recognized by other cells, helping to indicate cell identity.

Question 8

A scientist isolates glycoproteins from the surface of a mouse egg and separates the protein and carbohydrate components. Sperm are exposed to each component separately. What result would support the hypothesis that sperm recognize eggs by binding to the carbohydrate component?

Accepted Answer

Sperm exposed to the carbohydrate component show reduced attachment to eggs.

Question 9

Which of the following is a correct description of a condensation reaction in carbohydrate chemistry?

Accepted Answer

A condensation reaction joins two monosaccharides by forming a glycosidic bond and releasing a molecule of water.

Question 10

Which of the following polysaccharides is found in the exoskeletons of insects and the cell walls of fungi?

Accepted Answer

Chitin

Question 11

Which of the following statements about ring formation in sugars is correct?

Accepted Answer

Sugars tend to form ring structures in aqueous solutions due to reactions between the carbonyl group and a hydroxyl group.

Question 12

Which of the following is a correct statement about the arrangement of hydroxyl groups in glucose and galactose?

Accepted Answer

Glucose and galactose differ in the orientation of the hydroxyl group at carbon 4.

Question 13

Which of the following best explains why polysaccharides like cellulose are important for plant cells?

Accepted Answer

Cellulose provides structural support as a major component of the cell wall.

Question 14

Which of the following is a correct description of the difference between amylose and amylopectin?

Accepted Answer

Amylose is unbranched and contains only $	ext{α}$-1,4-glycosidic linkages, while amylopectin is branched and contains both $	ext{α}$-1,4 and $	ext{α}$-1,6-glycosidic linkages.

Question 15

Which of the following is a function of carbohydrates in living organisms?

Accepted Answer

Carbohydrates serve as building blocks for the synthesis of other molecules, store chemical energy, provide structural materials, and indicate cell identity.

Question 16

Which of the following best describes the difference between a condensation and a hydrolysis reaction?

Accepted Answer

Condensation reactions join monomers and release water; hydrolysis reactions break polymers and consume water.

Question 17

Which of the following molecules is most likely to have the highest potential energy stored in its bonds?

Accepted Answer

A carbohydrate molecule, because its carbon atoms are bonded to hydrogen and hydroxyl groups, which have higher energy than carbon-oxygen double bonds.

Question 18

Which of the following is true about glycosidic linkages in polysaccharides?

Accepted Answer

Glycosidic linkages can form between any two hydroxyl groups of monosaccharides, resulting in diverse polysaccharide structures.

Carbohydrates: Structure, Function, and Biological Importance

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