Carbohydrates
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MCAT Biology › Carbohydrates
Which of the following carbohydrates is created in animals, but not in plants?
Glycogen
Starch
Cellulose
Amylose
Explanation
Glucose is stored in animals cells in the form of glycogen. Plants store glucose as either starch or cellulose. Amylose is a specialized component of starch, and plays a key role in plant energy storage.
Plants do not form glycogen, similar to the way that humans cannot form (or break down) cellulose.
Which of the following carbohydrates is created in animals, but not in plants?
Glycogen
Starch
Cellulose
Amylose
Explanation
Glucose is stored in animals cells in the form of glycogen. Plants store glucose as either starch or cellulose. Amylose is a specialized component of starch, and plays a key role in plant energy storage.
Plants do not form glycogen, similar to the way that humans cannot form (or break down) cellulose.
Which of the following statements is true concerning glucose polymers?
Humans lack the enzyme that can break down the beta linkages in cellulose.
Humans do not eat foods that contain cellulose.
Starch is a glucose polymer held together by an 
Glucose is not favored in the body in ring form.
Explanation
Glucose is the primary carbohydrate absorbed by humans, and exists for its majority of time in the body in ring form. Humans are only capable of digesting alpha linked glucose polymers, and are unable to break down beta linked polymers. As a result, cellulose is incapable of being broken down by humans.
Starch is formed by an 
Which carbon in a carbohydrate determines whether a human is capable of digesting it properly?
The first chiral carbon
All chiral carbons affect its digestion capabilities
The carbonyl carbon
The anomeric carbon
Explanation
Humans are only capable of digesting the "D" isomer of a carbohydrate. The carbon that determines whether a carbohydrate is "D" or "L" is the first chiral carbon in the sugar. If it points to the right, the sugar can be digested by humans.
Cellulose is a type of carbohydrate used in plants to store glucose. Cellulose cannot be broken down by humans, but is able to be digested by ruminants (cows for example). What is the best explanation for why ruminants are able to digest cellulose?
Ruminants house bacteria in their digestive tracts that are able to break down the cellulose
Ruminants have four stomachs which allow them to digest food for a much longer time
Ruminants create an enzyme that allows them to digest cellulose
Ruminants rearrange the molecular configuration of cellulose, allowing it to be digested by other enzymes
Ruminants have a stomach pH of roughly 2.5
Explanation
Cellulose and other polysaccharides with beta linkages can only be broken down by bacteria. As a result, cows have a symbiotic relationship with bacteria that live in their digestive systems.
Which carbon in a carbohydrate determines whether a human is capable of digesting it properly?
The first chiral carbon
All chiral carbons affect its digestion capabilities
The carbonyl carbon
The anomeric carbon
Explanation
Humans are only capable of digesting the "D" isomer of a carbohydrate. The carbon that determines whether a carbohydrate is "D" or "L" is the first chiral carbon in the sugar. If it points to the right, the sugar can be digested by humans.
Which of the following statements is true concerning glucose polymers?
Humans lack the enzyme that can break down the beta linkages in cellulose.
Humans do not eat foods that contain cellulose.
Starch is a glucose polymer held together by an
Glucose is not favored in the body in ring form.
Explanation
Glucose is the primary carbohydrate absorbed by humans, and exists for its majority of time in the body in ring form. Humans are only capable of digesting alpha linked glucose polymers, and are unable to break down beta linked polymers. As a result, cellulose is incapable of being broken down by humans.
Starch is formed by an
Cellulose is a type of carbohydrate used in plants to store glucose. Cellulose cannot be broken down by humans, but is able to be digested by ruminants (cows for example). What is the best explanation for why ruminants are able to digest cellulose?
Ruminants house bacteria in their digestive tracts that are able to break down the cellulose
Ruminants have four stomachs which allow them to digest food for a much longer time
Ruminants create an enzyme that allows them to digest cellulose
Ruminants rearrange the molecular configuration of cellulose, allowing it to be digested by other enzymes
Ruminants have a stomach pH of roughly 2.5
Explanation
Cellulose and other polysaccharides with beta linkages can only be broken down by bacteria. As a result, cows have a symbiotic relationship with bacteria that live in their digestive systems.
Drain cleaners a common household staple, used to open clogged drains in bathtubs and sinks. Human hair is a common culprit that clogs pipes, and hair is made predominately of protein. Drain cleaners are effective at breaking down proteins that have accumulated in plumbing. Drain cleaners can be either acidic or basic, and are also effective at breaking down fats that have accumulated with proteins.
A typical reaction—reaction 1—which would be expected for a drain cleaner on contact with human hair, would be as follows in an aqueous solution:
Another reaction that may occur, reaction 2, would take place as follows in an aqueous solution:
In contrast to the proteins in Reactions 1 and 2, the body uses carbohydrates __________.
to store energy for immediate use
to store energy for use over many days
to create strucutral elements of cells
to dissolve nonpolar solutes in blood
to function as a secondary energy source after fatty acids have been oxidized
Explanation
Carboydrates are the main energy currency of cells. They are typically burned first, before fats and proteins, to generate energy. Proteins, in contrast, are usually the functional biomolecules, serving structural and enzymatic roles.
Which of the following accurately describes glucose?
Aldohexose
Ketohexose
Ketopentose
Aldopentose
Explanation
Glucose is composed of six carbons. When not in ring form, there is an aldehyde at the end of the molecule. As a result, glucose is an example of an aldohexose.