AP Bio Unit 1 Quiz
Questions: 16 · 10 minutes
1. During dehydration synthesis, how are two biological subunits typically joined?
A water molecule is added, breaking a covalent bond between the subunits.
Components of a water molecule are removed as a new covalent bond forms.
Both subunits gain phosphate groups and become ions.
Hydrogen bonds permanently replace all covalent bonds between the subunits.
2. Which feature is characteristic of a phospholipid?
It is a polymer made entirely from repeating glucose monomers.
It contains an amino group, a carboxyl group, and a variable R group.
It has a polar phosphate-containing region and nonpolar fatty-acid tails.
It consists of a nitrogenous base attached to two amino acids.
3. Why can a change in a protein’s primary structure alter its biological function?
Primary structure determines how many nucleotide bases the protein contains.
Changing one amino acid always breaks every peptide bond in the protein.
The amino acid sequence influences the interactions that produce the protein’s shape.
Primary structure affects function only when the protein contains carbohydrates.
4. An enzyme works well at pH 7 but loses most of its activity at pH 2. What is the most direct molecular explanation?
The enzyme becomes a lipid because acids are nonpolar.
The acidic solution changes every amino acid into a monosaccharide.
Low pH removes all peptide bonds but leaves the enzyme’s shape unchanged.
Changes in proton concentration can alter side-chain charges, disrupting the enzyme’s shape or active site.
5. Starch and cellulose are both built from glucose, yet humans readily digest starch but not cellulose. What best explains this difference?
Their glucose subunits have different linkages, and human enzymes do not hydrolyze cellulose’s beta linkages.
Cellulose contains amino acids in place of some of its glucose monomers.
Starch is a lipid, whereas cellulose is a carbohydrate.
Cellulose has no covalent bonds between its glucose subunits.
6. A cell membrane must remain functional as its environment becomes colder. Which lipid change would generally help preserve membrane fluidity?
Replacing phospholipids with long chains of covalently bonded amino acids
Increasing the proportion of unsaturated fatty-acid tails, whose bends limit tight packing
Increasing only straight, saturated tails so the lipids pack more closely
Removing polar heads so every phospholipid becomes completely nonpolar
7. Sweating can cool the body when water evaporates from the skin. What most directly produces this cooling effect?
Higher-energy water molecules escape, lowering the average kinetic energy of the water left behind.
Water releases stored chemical energy when its covalent bonds break.
Hydrogen bonds make water vapor denser than liquid water.
Evaporation converts water molecules into nonpolar molecules.
8. A mutation replaces a charged amino acid on a protein’s surface with a nonpolar amino acid. Which outcome is most reasonable?
Different side-chain interactions may change the protein’s folding or interactions with water.
The protein will necessarily be converted into a carbohydrate.
The protein must gain a new nucleotide at the same location.
The mutation cannot affect the protein because all amino acids have identical chemical properties.
9. Which statement correctly distinguishes typical RNA structure from DNA structure?
RNA usually contains deoxyribose, while DNA contains ribose.
RNA uses thymine, while DNA uses uracil.
RNA is always double-stranded, while DNA is always single-stranded.
RNA typically contains ribose and uracil, while DNA contains deoxyribose and thymine.
10. Which example best represents a hydrogen bond that can help stabilize protein structure?
Two nonpolar side chains cluster away from surrounding water.
Two cysteine side chains form a covalent disulfide bond.
A positively charged side chain attracts a negatively charged side chain.
A partially positive N–H hydrogen is attracted to a partially negative carbonyl oxygen.
11. What property of carbon makes it especially useful as a framework for diverse biological molecules?
It has eight valence electrons available for bonding.
It normally forms only ionic bonds with other carbon atoms.
It can form four covalent bonds and build chains, branches, and rings.
It cannot bond with hydrogen, so its structures remain stable in water.
12. Why is a water molecule polar?
Hydrogen transfers both of its electrons completely to oxygen.
Oxygen attracts the shared electrons more strongly than hydrogen, producing partial charges.
The two O–H bonds share electrons equally but point in opposite directions.
Oxygen and hydrogen become ions whenever they form water.
13. Which three components make up a nucleotide?
A five-carbon sugar, a phosphate group, and a nitrogenous base
An amino group, a carboxyl group, and an R group
Glycerol, a phosphate group, and a fatty acid
A six-carbon sugar, a peptide group, and a nitrogenous base
14. A pond freezes at its surface while liquid water remains below. Which molecular explanation best accounts for the ice staying on top?
Frozen water molecules lose their polarity and repel liquid water.
Covalent O–H bonds become longer in ice, making each molecule lighter.
Ionic bonds form in ice and push its molecules toward the surface.
Hydrogen bonds hold water molecules in an open lattice, making ice less dense than liquid water.
15. A digestive enzyme splits a polysaccharide into smaller sugars. Which process is occurring?
Dehydration synthesis, because water is released from each bond
Hydrolysis, because water is used to break covalent bonds
Denaturation, because the sugar changes its three-dimensional shape
Neutralization, because the polysaccharide gains and loses protons
16. Which interaction is a hydrogen bond between two water molecules?
The covalent bond joining oxygen and hydrogen within one molecule
The attraction between the two hydrogen atoms of neighboring molecules
The attraction between one molecule’s partially positive hydrogen and another molecule’s partially negative oxygen
The sharing of an electron pair by the oxygen atoms of neighboring molecules