AP Biology: Chemistry of Life — Practice Questions & Answers
Life depends on the unique properties of water and on a small set of elements that build four classes of carbon-based macromolecules through dehydration synthesis.
432 practice questions available for this unit — here are 10 with full answers and explanations.
Water molecules are described as polar. Which feature of a water molecule is most directly responsible for this polarity?
The two hydrogen atoms repel each other and bend the molecule
Oxygen is more electronegative than hydrogen, creating an uneven distribution of charge
Water molecules form ionic bonds with one another
The hydrogen atoms each carry a full negative charge
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WhyOxygen is more electronegative than hydrogen, so the shared electrons spend more time near oxygen. This creates a partial negative charge on oxygen and partial positive charges on the hydrogens, making the molecule polar.
2Multiple choice · Easy
Which property of water allows some insects to walk across the surface of a pond without sinking?
Surface tension produced by cohesion between water molecules
The high specific heat of water
The ability of water to act as a universal solvent
Adhesion between water and the insect's body
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WhyCohesion among water molecules at the surface produces surface tension, an inward pull that resists external force and creates a film strong enough to support small organisms.
3Multiple choice · Easy
The elements carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur make up the majority of biological macromolecules. Which of these elements is found in the side chains of certain amino acids and helps form disulfide bridges in proteins?
Phosphorus
Nitrogen
Sulfur
Carbon
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WhySulfur is present in the amino acids cysteine and methionine. The thiol (-SH) groups of two cysteines can form disulfide bridges that stabilize protein tertiary structure.
4Multiple choice · Easy
Which statement correctly describes dehydration synthesis (condensation)?
A water molecule is removed as two monomers are joined together
A water molecule is added to split a polymer into monomers
Monomers are joined without any change in the number of water molecules
A phosphate group is removed to join two monomers
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WhyIn dehydration synthesis, a covalent bond forms between two monomers and a water molecule is removed. This is how polymers such as polysaccharides, proteins, and nucleic acids are assembled.
5Multiple choice · Easy
Glucose, fructose, and galactose are all monosaccharides with the molecular formula C6H12O6. The relationship among these three molecules is best described as that of
polymers
isomers
monomers of protein
saturated fatty acids
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WhyMolecules with the same molecular formula but different structural arrangements are isomers. Glucose, fructose, and galactose all share C6H12O6 but differ in atom arrangement.
6Multiple choice · Easy
A nucleotide is the monomer of nucleic acids. Which three components make up a single nucleotide?
A pentose sugar, a phosphate group, and a nitrogenous base
An amino group, a carboxyl group, and an R group
Glycerol, a fatty acid, and a phosphate group
Two monosaccharides joined by a glycosidic bond
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WhyEvery nucleotide consists of a five-carbon (pentose) sugar, a phosphate group, and a nitrogenous base. These join to form the polymer DNA or RNA.
7Multiple choice · Easy
Which of the following best explains why water is referred to as the universal solvent in biological systems?
Its polarity allows it to surround and dissolve charged and polar substances
It has a low specific heat that prevents temperature change
It is nonpolar and dissolves lipids easily
It forms covalent bonds with all solutes it contacts
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WhyBecause water is polar, it surrounds and separates charged or polar (hydrophilic) solutes, dissolving them. This makes water an excellent medium for transporting nutrients and other solutes.
8Multiple choice · Medium
Water has an unusually high specific heat compared with most other liquids. Which of the following is the best explanation for this property?
Water molecules are nonpolar and resist movement
A large amount of heat is needed to break the many hydrogen bonds between water molecules
Water has a very low molecular mass
Covalent bonds within each water molecule absorb most of the added heat
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WhyHydrogen bonds between water molecules must absorb a large amount of energy before the molecules move faster (temperature rise). This network of hydrogen bonds gives water a high specific heat, helping organisms resist temperature change.
9Multiple choice · Medium
Capillary action moves water upward through the narrow xylem of a plant against gravity. This phenomenon depends on two properties of water working together. They are
specific heat and density
adhesion to the vessel walls and cohesion among water molecules
surface tension and evaporation only
polarity and nonpolar interactions
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WhyAdhesion attaches water to the polar walls of the xylem, while cohesion holds the column of water molecules together. Together they pull a continuous water column upward.
10Multiple choice · Medium
A scientist hydrolyzes a disaccharide and recovers two monosaccharide molecules. Based on the chemistry of hydrolysis, which additional reactant was required for this reaction?
A water molecule
A phosphate group
An additional monosaccharide
A molecule of ATP only
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WhyHydrolysis breaks a covalent bond by adding water; the components of a water molecule (-H and -OH) are added across the broken bond. Therefore water is consumed as a reactant.
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Atom: The smallest unit of an element that still retains the chemical properties of that element, consisting of a nucleus of protons and neutrons surrounded by electrons.
Element: A pure substance made of only one kind of atom that cannot be broken down into simpler substances by ordinary chemical reactions.
Proton: A positively charged subatomic particle found in the atomic nucleus; its number defines the identity (atomic number) of an element.
Neutron: An electrically neutral subatomic particle in the atomic nucleus that contributes to an atom's mass and determines its isotope.
Electron: A negatively charged subatomic particle that occupies regions around the nucleus and participates in chemical bonding.
Atomic number: The number of protons in an atom's nucleus, which uniquely identifies an element.
Mass number: The total count of protons and neutrons in an atom's nucleus.
Isotope: An atom of a given element that has the same number of protons but a different number of neutrons than other atoms of that element.