AP Biology : Understanding Carbohydrates

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Understanding Carbohydrates

Which of the following is one of the primary functions of carbohydrates?

Possible Answers:

Catalyze chemical reactions

Maintain genetic fidelity

Protect cell organelles

Energy storage

Correct answer:

Energy storage

Explanation:

Carbohydrates, such as glucose and fructose, are primarily used in metabolic pathways to provide energy for the cell. Glucose is the first reactant necessary for driving glycolysis and subsequent cellular respiration in the cell, with the goal of producing ATP.

Proteins and enzymes serve to catalyze reactions. Nucleic acids store genetic material. Lipids form the membranes that surround and protect organelles.

Example Question #2 : Understanding Carbohydrates

Which of the following is a carbohydrate?

Possible Answers:

Lipase

Mannose

Cholesterol

miRNA

Correct answer:

Mannose

Explanation:

Mannose is an epimer of glucose, and is a carbohydrate. Typically, molecule names ending in "–ose" will be carbohydrates. The other answers each belong to a different category of macromolecule: cholesterol is a lipid, miRNA is a nucleic acid, and lipase is a protein.

Just as the suffix "ose" signifies a carbohydrate, the suffix "ol" indicates a lipid and the suffix "ase" indicates a protein.

Example Question #41 : Macromolecules

Beta amylase is an enzyme that breaks down polysaccharides into component monosaccharides, but is not produced by humans. Beta amylase is most effective in digesting which of the following?

Possible Answers:

Cellulose

Glucose

Glycogen

Starch

Correct answer:

Cellulose

Explanation:

Starch and glycogen have alpha glycosidic bonds between each glucose molecule. Humans can digest starch and glycogen because humans possess alpha amylase, which breaks these alpha linkages.

Cellulose contains beta glycosidic bonds, which can be digested by beta amylase. Since humans do not possess beta amylase protein, they are unable to digest cellulose.

Starch and cellulose are polysaccharides that are found in plants and glycogen is found in human liver. All three polysaccharides are made from glucose, a monosaccharide.

Example Question #42 : Macromolecules

Which of the following carbohydrates does not have a molecular formula of ?

Possible Answers:

Glucose

Ribose

Galactose

Mannose

Correct answer:

Ribose

Explanation:

Carbohydrates have an empirical formula of . The most common types of carbohydrates are pentoses (5-carbon carbohydrates) and hexoses (6-carbon carbohydrates). All 6-carbon carbohydrates share the molecular formula .

Glucose, galactose, and mannose are all hexoses. The only difference between these three carbohydrates is their relative orientation of hydroxyl groups on the carbons.

Ribose is a pentose, and has a different molecular formula. Remember that all nucleic acids contain 5-carbon rings.

Example Question #43 : Macromolecules

Which of the following statements is true regarding glycogen?

Possible Answers:

Increased levels of insulin will increase the amount of glycogen stored in the liver

Decreased levels of glucagon promotes breakdown of glycogen into galactose

Decreased levels of insulin promotes breakdown of glycogen into galactose

Increased levels of insulin will increase the amount of glycogen stored in the pancreas

Correct answer:

Increased levels of insulin will increase the amount of glycogen stored in the liver

Explanation:

Recall that glucagon promotes the breakdown of glycogen to glucose, whereas insulin promotes formation of glycogen from glucose molecules. Both hormones function to regulate glucose levels. You can eliminate choices with galactose because glycogen is made up of glucose, not galactose.

You can also eliminate the answer choice that suggests that glycogen is stored in the pancreas. The pancreas releases the hormones insulin and glucagon, but it doesn’t store glycogen. The glycogen is actually stored in the liver. Increased levels of insulin increase the amount of glycogen stored in the liver.

Example Question #44 : Macromolecules

What is the main source of carbohydrates used in the human body for energy?

Possible Answers:

Lactose

Fructose

Sucrose

Glucose

Galactose

Correct answer:

Glucose

Explanation:

Glucose is the main source of energy in the human body. It is a six carbon sugar that, when fully oxidized, can yield as many as 36 ATP. The brain in the human body uses glucose exclusively, though other parts of the body are capable of metabolizing other sugars. When complex sugars are ingested, they are broken down and converted by various enzymes to produce glucose. The glucose then enters into glycolysis to generate cellular energy.

Example Question #45 : Macromolecules

When does glycolysis occur?

Possible Answers:

When insulin levels are high

During the catabolism of proteins

During both anaerobic and aerobic respiration

During the catabolism of fatty acids

During fermentation only

Correct answer:

During both anaerobic and aerobic respiration

Explanation:

Glycolysis occurs within the cytosol of the cell, during both aerobic and anaerobic respiration. Glycolysis is the first step to generate energy from the breakdown of carbohydrates. 

Glycolysis does not involve the breakdown of proteins or fatty acids. Fermentation can be used to regenerate NAD+, with a byproduct of lactic acid or ethanol, during anaerobic respiration. Glycolysis will occur simultaneous to fermentation, but will also occur during healthy aerobic respiration.

Example Question #46 : Macromolecules

Which of the following is not a basic biological building block?

Possible Answers:

Nucleotide

Amino acid

Enzyme

Fatty acid

Monosaccharide

Correct answer:

Enzyme

Explanation:

Enzymes are proteins, which are composed of amino acids. Biomolecules are made of polymers. The monomers in nucleic acids are nucleotides. The monomers in carbohydrates are monosaccharides. Lipids are biomolecules, but their structure does not follow as clear of a pattern as the other three. Depending on the textbook, we may consider fatty acids, or hydrocarbons as "monomers" of lipids. There is some ambiguity with lipids because their structures are diverse and are not always chains of repeating subunits.

Example Question #47 : Macromolecules

Which of the following is a polymer composed of sugar monomers?

Possible Answers:

Lipids

Lactose

Carbohydrates

Glucose

Proteins

Correct answer:

Carbohydrates

Explanation:

Carbohydrates and proteins are polymers (a long chain molecule generally composed of repeating single units), but glucose and lipids are not polymers (though glucose has the ability to polymerize). Proteins are polymers of amino acids. Carbohydrates are polymers of sugar monomers or monosaccharides. Lactose is a disaccharide or two sugar monomers connected. 

Example Question #48 : Macromolecules

Which of the following terms is defined as the process by which water breaks polymers down into monomers?

Possible Answers:

Anabolic reaction

Condensation synthesis reaction

None of these

Hydrolysis

Correct answer:

Hydrolysis

Explanation:

Polymers are broken down into monomers via hydrolysis. Hydrolysis is the reverse of a condensation synthesis reaction. In hydrolysis, adding water molecules breaks the bonds between monomers. In this reaction polymers are broken down when the hydrogen of the water molecules attaches to one monomer and the hydroxyl attaches the next monomer.

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