Name___________________________________Date__________Period___________
Unit 2
Keystone Review
1. In most animal cells, a complex network of proteins provides
A. movement
B. organization
C. shape
D. all of these
2. Polymers of the carbohydrate monomer glucose are used as the major form of energy storage
for many plants. What are these glucose polymers called?
A. starch
B. glycogen
C. table sugar
D. maltose
3. Nitrogen atoms are part of the structure of some organic molecules, such as all amino acids
and some modified carbohydrates. What other organic molecules contain nitrogen?
A. nucleotides
B. starch
C. fatty acids
D. cellulose
4. Which of the following are examples of nucleic acids?
A. saturated fats and unsaturated fats
B. DNA and RNA
C. glucose and starch
D. collagen and keratin
5. Which of the following is true about protein molecules?
Protein molecules are made up of strands of DNA joined together by amino acid
A. sequences.
B.
The sequence of amino acids that make up a protein molecule do not affect its function.
Protein molecules have many functions in the body, including the storage of genetic
C. information.
The shape and folded structure of a protein molecule are important in determining its
D. function.
6. Nucleic acids are one of the four major macromolecules.
The main functions of nucleic acids are to
A. store and transport energy and structural components in the cell.
B. aid in development, the immune system, and blood clotting.
C. carry genetic material and create structures inside the cell.
D. act as enzymes, cell signals, and structural support for the cell.
7. Examine the diagram of the enzyme below:
How does the structure of this enzyme help with its function?
A.
The enzyme's shape complements the substrate's shape, so it only catalyzes specific
reactions.
B. Since the enzyme's shape matches the substrate's shape, it catalyzes only reverse reactions.
Since the enzyme is larger than the substrate, catalytic reactions can occur within the
C.
enzyme itself.
D. The enzyme's active site is amorphous and can change its shape to fit any substrate.
8. A polymer is a large molecule that forms when smaller molecules known as monomers bond
covalently in a repeating pattern. There are many biological polymers such as nucleic acids,
proteins, and starches.
What are the monomer units that make up nucleic acids?
A. fatty acids
B. nucleotides
C. glucose
D. amino acids
9. Organic macromolecules called _______ are insoluble in water, are often found in biological
membranes and other waterproof coverings, and have the ability to store energy for extended
periods of time.
A. nucleic acids
B. carbohydrates
C. lipids
D. proteins
10. Which of the following is true about nucleic acids?
I. Nucleic acids always consist of a five-carbon sugar, a nitrogenous base, and one or more
phosphate groups.
II. Both DNA, which stores genetic information and encodes protein sequences, and RNA,
which is involved in the direct production of proteins, are nucleic acids.
III. Nucleic acids are usually insoluble in water and are used for long term energy storage.
IV. Glucose, cellulose, and starch are examples of nucleic acids found in most cells.
A. I, II, III, and IV
B. II only
C. I, III, and IV only
D. I and II only
11. A large carbohydrate molecule is composed of several subunits, such as glucose.
An example of a large carbohydrate molecule is _______.
A. cellulose
B. glycogen
C. starch
D. all of these
12. All living organisms contain carbon atoms. Which of the following is an important
characteristic of carbon?
A.
B.
C.
Carbon atoms are very stable and do not easily form bonds with other atoms.
Carbon atoms are highly reactive and form unstable bonds with any available atom.
Carbon atoms can bond with many other kinds of atoms to form very stable molecules.
Carbon atoms can bond with any other atom, but they cannot form bonds with other
D. carbon atoms.
13. Protein molecules are composed of long chains of _______.
A. DNA
B. RNA
C. amino acids
D. ribosomes
14. Lakes and oceans are able to stabilize air and land temperatures because
water is able to absorb large amounts of heat without significantly changing its
A. temperature.
the temperature of water changes significantly instead of the temperature of the air and
B. land.
C.
D.
the water is able to release large amounts of heat into the air when necessary.
the salt in the water bodies is able to absorb large amounts of heat.
15. DNA molecules store genetic information and allow for self-replicating life. Molecules of
DNA can be long and very complex. They always consist of smaller molecules that are made up
of nitrogenous bases, phosphate groups, and 5-carbon sugars.
DNA is an example of a complex _______.
A. organic molecule
B. protein structure
C. carbohydrate polymer
D. inorganic molecule
16. Sugars such as glucose, fructose, and ribose are examples of _______.
A. nucleic acids
B. proteins
C. lipids
D. carbohydrates
17. Water is important to plant cells because it is used as one of the reactants in the process of
photosynthesis. What is another reason why water is important to plant cells?
A. Water helps to maintain turgidity in plant cells.
B. Water is a major structural component found in plant cell walls.
C. Water signals plant DNA to start transcription and translation.
D. Water can be used as a substitute for glucose in times of distress.
18. In which of the following are lipids found?
A. in some vitamins and steroids
B. in biological membranes
C. in saturated and unsaturated fats
D. all of these
19. Water is the most abundant molecule found in living organisms. Most mammals, in fact, are
approximately 70% water by weight. About two-thirds of this water is present inside cells. The
other one-third is present outside cells (e.g., in blood plasma or other body fluids). Why is water
so important to cells?
A. The main structural component found in plasma membranes and cell walls is water.
B. Water determines which proteins are translated from the cellular DNA.
C. Water is stored in the cells to be used when the organism gets thirsty.
D. Almost all the chemical reactions in life processes occur in solutions with water.
20. Carbohydrates, such as glucose, are excellent sources of immediate energy for living
organisms. More complex carbohydrates, such as glycogen and starch, can also be used for the
long term storage of energy. However, carbohydrates play other vital roles, too. Which of the
following describes another common use for carbohydrates?
A. Cellulose is used as a structural component in plant cell walls.
B. Keratin provides support in hair, nails, feathers, hooves, and some animal shells.
C. Collagen is a major component in cartilage and tendons.
D. Enzymes help speed up metabolic reactions.
21. Which of the following are the important, life-sustaining properties of water?
I. cohesive behavior
II. ability to moderate temperature
III. expansion upon freezing
IV. versatility as a solvent
A. II and III only
B. I and III, and IV only
C. I, II, III, and IV
D. I, II, and IV only
22. A _______ is a kind of lipid that can store energy for a long period of time. These lipids are
made up of long chains of carbon and oxygen atoms bonded to a backbone structure.
A. fat
B. nucleic acid
C. carbohydrate
D. protein
23. Lipids are organic macromolecules that serve a variety of purposes. What is the most
important role of lipids?
A. to store energy
B. to metabolize sugar
C. to build muscles
D. to oxygenate blood
24. Carbohydrates are biological molecules that contain carbon, hydrogen, and oxygen.
Polysaccharides are biological polymers because they contain repeating patterns of monomer
subunits.
Amylose is a polysaccharide that serves as one of two components in starches.
Glycogen is also a polysaccharide used to store energy in animal cells.
How does the structure of amylose compare to the structure of glycogen?
A. They contain different monomer subunits but they are arranged in the same pattern.
B. They contain the same monomer subunits and they are arranged in the same pattern.
C. They contain different monomer subunits and they are arranged differently.
D. They contain the same monomer subunits but they are arranged differently.
25. Which of the following best describes a carbohydrate?
Carbohydrates always consist of a five-carbon sugar, a nitrogenous base, and one or more
A. phosphate groups and are used to store genetic information.
Carbohydrates are composed of amino acid monomers and are involved in cell signaling,
B. cell transport, immune responses, and the cell cycle.
Carbohydrates are organic macromolecules that are insoluble in water and have the ability
C. to store energy for extended periods of time.
Carbohydrates are organic macromolecules that are made up of carbon, hydrogen, and
D. oxygen atoms and are used for energy storage or as structural molecules.
26. What role do ATP and NADH play in living cells?
A. They provide structural support to cell membranes.
B. They store and transfer energy.
C. They also store and transfer information.
D. They are involved in cell-to-cell signaling.
27. All living things contain carbon. Which of the following statements are true about carbon
atoms?
I. Each carbon atom can form single bonds with up to four other carbon atoms.
II. Each carbon atom can form double bonds with up to two other carbon atoms.
III. Carbon atoms can join together to form chains or rings.
IV. A single molecule of some compounds can contain thousands of carbon atoms.
A. I, II, and III only
B. I and III only
C. I, II, III, and IV
D. II and III only
28. Proteins are used for many structural functions such as in the actin and myosin in muscle or
as a part of the cytoskeleton scaffolding that maintains cell shape. What other main function do
proteins serve?
A. as cellulose to form the major structural component of plant cell walls
B. as enzymes to control the rate of reactions and regulate cellular activity
C. as waterproof membranes to regulate the transport of molecules in and out of the cell
D. as coding for genotypic expression and phenotypic traits
29. Carbon atoms have four electrons in their outer shell. This means that a single carbon atom
can form up to _______ bonds with other atoms.
A. six
B. two
C. four
D. eight
30. Suppose that the temperature in the ecosystem below dips below freezing.
What would happen to the fish swimming in the lake?
A. The fish would die because the lake would freeze solid.
B. Ice would form on the surface of the lake and insulate the fish.
C. The fish would move more rapidly to increase their body temperature.
D. Ice would only form on the bottom of the lake, so the fish would be okay.
Answers
1. D
2. A
3. A
4. B
5. D
6. C
7. A
8. B
9. C
10. D
11. D
12. C
13. C
14. A
15. A
16. D
17. A
18. D
19. D
20. A
21. C
22. A
23. A
24. D
25. D
26. B
27. C
28. B
29. C
30. B
Explanations
1. In most animal cells, a complex network of proteins provides organization, shape, and
movement. In all cells, other than very primitive ones, the network of proteins provides
organization and shape.
Most of these structural proteins that provide organization and shape are fibrous proteins, such as
actin and tubulin. Most of the motor proteins are made up of myosin and kinesin.
2. Though polymers of glucose are a common form of energy storage, they have different
structures (and names) based on which carbon atom is involved in the glycosidic linkage. In
animals, the polymers synthesized are glycogen; in plants, they are starches.
3. All nucleotides are made up of three component compounds:



a 5-carbon sugar (ribose or deoxyribose),
a phosphate group, and
a nitrogenous base.
The nitrogenous bases are a group of compounds with a complex one- or two-ring structure
made up of carbon and nitrogen atoms in single and double bond combinations.
4. There are two main types of nucleic acids - ribonucleic acids (RNA) and deoxyribonucleic
acids (DNA). These nucleic acids are different because their five-carbon sugars are different.
RNA contains ribose, and DNA contains deoxyribose. DNA and RNA also have different
functions. DNA stores genetic information and encodes the sequences of all the cell's proteins
whereas RNA is involved in the direct production of the proteins.
5. Protein molecules are composed of long chains of amino acids and perform many functions in
the human body. The function of a protein molecule is determined by the sequence of its amino
acids and its shape/folded structure.
Proteins do not, however, store genetic information. Genetic information is stored by sequences
of DNA.
6. The main functions of nucleic acids are to carry genetic material and create structures
inside the cell.
A nucleic acid is a macromolecule that is made up of chains of nucleotides. The two main types
of nucleic acids are DNA and RNA.
7. The shape of an enzyme determines how it works. Most enzymes have a surface with one or
more deep folds. The folds make pockets which are called active sites.
The active sites match folds in the substrate's surface, like a key matches a lock, so the enzyme
only catalyzes specific reactions. Once an enzyme binds to a substrate, the amount of energy
needed to start a chemical reaction with the substrate is reduced.
8. Cells can make a variety of macromolecules from a relatively small set of monomers.
Starches are made up of hundreds of glucose monomers bonded together. Starches are a common
storage form for glucose.
Proteins are made up of amino acid monomers. Proteins play many structural and metabolic roles
in organisms.
Nucleic acids are made up of nucleotides. A nucleotide consists of a five-carbon sugar, a
phosphate group, and a nitrogenous base. In DNA, the five-carbon sugar is deoxyribose. In
RNA, the five-carbon sugar is ribose.
9. Organic macromolecules called lipids are insoluble in water which is why lipids are often
found in biological membranes and other waterproof coverings. Lipids also play a vital role in
insulation, regulating which substances can or cannot enter a cell, and they have the ability to
store energy for extended periods of time.
10. Nucleic acids are formed from nucleotide monomers and are primarily comprised of the
elements carbon, hydrogen, oxygen, nitrogen, and phosphorus. They always consist of a fivecarbon sugar, a nitrogenous base, and one or more phosphate groups.
There are two main types of nucleic acids - ribonucleic acids (RNA) and deoxyribonucleic acids
(DNA). These nucleic acids are different because their five-carbon sugars are different. RNA
contains ribose, and DNA contains deoxyribose. DNA and RNA also have different functions.
DNA stores genetic information and encodes the sequences of all the cell's proteins whereas
RNA is involved in the direct production of the proteins.
Only I and II are true about nucleic acids. Lipids are usually insoluble in water and are used for
long term energy storage. Glucose, cellulose, and starch are examples of carbohydrates.
11. Polysaccharides, or large carbohydrate molecules, are polymers that are made up of
monosaccharide subunits. Starch, cellulose, and glycogen are all examples of large
carbohydrate molecules.
Starch, cellulose, and glycogen are all composed of glucose subunits linked in different ways.
Starches have branched chains of glucose subunits and are used as food storage for plants.
Glycogen has more highly branched chains of glucose than starch and is used by animals instead
of plants. Cellulose is a mostly straight chain of glucose subunits and is used to form the cell
wall of plants.
12. Carbon atoms can bond with many other kinds of atoms to form very stable molecules.
This is because carbon atoms have four electrons in their outer shells, and all four are available
for bonding.
Carbon can share these electrons in single bonds with up to four other atoms to form very stable
structures. Alternatively, carbon can form double bonds with up to two other atoms by sharing
two electrons with each. Carbon can also form a combination of double and single bonds, as long
as no more than four electrons are donated.
13. There are over 20 different kinds of amino acids, which, when connected in long chains,
form protein molecules.
These long chains are usually folded into specific conformations. The sequence of amino acids
and the shape of the chain are a result of attractions between the chain's parts.
14. Water has a high specific heat. This means that water is able to absorb large amounts of
heat energy without significantly changing its temperature. One effect of water's high
specific heat is that lakes and oceans are able to stabilize air and land temperatures.
15. Nucleic acids, such as DNA, are formed from nucleotide monomers. Nucleotides are
chemical compounds that consist of a five-carbon sugar, a nitrogenous base, and one or more
phosphate groups. All nucleic acids, including DNA, are organic molecules.
16. Sugars such as glucose, fructose, and ribose are all examples of monosaccharides, or simple
carbohydrates.
Carbohydrates are organic macromolecules that are made up of carbon, hydrogen, and oxygen
atoms. These atoms are combined in a ratio of
1 carbon atom : 2 hydrogen atoms : 1 oxygen atom
Simple carbohydrates can bond together to make polysaccharides, or larger, more complex
carbohydrates, such as starch or cellulose.
Carbohydrates are typically used for energy storage or as structural molecules.
17. Plant cells must retain their turgidity, or rigid structure, in order to effectively undergo
photosynthesis, because if a plant's stems or leaves wilt, the surfaces of the leaves will not be
able to properly absorb energy from the Sun.
Inside of plant cells are large vacuoles that hold water. These vacuoles can take up 30-90% of the
total volume of the plant cell. The water in these vacuoles helps to maintain turgidity in the
plant cells.
18. Due to the abundance of carbon-hydrogen bonds present in lipids, they are primarily used as
a source of energy for living organisms. Lipids, however, are found in a variety of other roles,
too.
Lipids are found in some fat-soluble vitamins and naturally occurring steroids, such as estrogen
and testoterone. Lipids are found in biological membranes and other waterproof coverings, such
as plasma membranes and the intracellular membranes of cellular organelles. Lipids are also
found in food in the form of saturated and unsaturated fats. Butter, cheese, oils, chocolate, beef,
fish, and mayonnaise are among the many foods in which fats are found.
19. Water is an extremely important molecule to cells because almost all the chemical
reactions in life processes occur in solutions with water. Without water, processes such as
photosynthesis and cellular respiration, or even simpler processes such as diffusion and osmosis,
could not occur. Also, cells would be unable to manufacture and transport ATP to provide
energy for the organism. Water is an essential molecule to all living things.
20. In addition to being an energy source for living organisms, carbohydrates play a structural
role, as well. Cellulose, for example, is a carbohydrate found in plant cell walls.
Keratin, collagen, and enzymes are all examples of proteins, not carbohydrates.
21. Water contains special properties that contribute to Earth's suitability as an environment for
life. These properties include, but are not limited to




cohesive behavior
ability to moderate temperature
expansion upon freezing, and
versatility as a solvent.
Cohesion is due to hydrogen bonding which contributes to the transport of water against gravity
in plants. Related to cohesion is surface tension, a measure of how difficult it is to stretch or
break the surface of a liquid. Rocks are able to skip across a pond due to the cohesion of the
water molecules, especially at the surface.
Water is known as a versatile solvent because it is a polar molecule. It dissolves other polar
molecules with great ease.
During the winter, large bodies of water, such as lakes, do not freeze solid because ice expands
and floats to the top to form an insulating layer that keeps the rest of the liquid water from
freezing. If water did not expand upon freezing, large bodies of water would likely freeze solid
during the winter, killing all the organisms that live in the water.
22. A fat is a kind of lipid that can store energy for a long period of time. Fats are made up of
long chains of carbon and oxygen atoms bonded to a backbone structure. This backbone
structure is often glycerol.
Fats are important because they are a major source of energy. Since they contain even more
carbon-hydrogen bonds than carbohydrates, fatty tissue has the ability to store energy for
extended periods of time.
23. Lipids are found as structural components of cell membranes and can also serve as signaling
molecules. Their most important role, however, is to store energy. In fact, lipids store over twice
as much energy (9 kcal/gram) as carbohydrates or proteins (4 kcal/gram).
24. Starches, glycogen, and cellulose are all examples of polysaccharides.
These biological polymers are similar because they all contain the same monomer subunits glucose. However, they possess different chemical properties because they are arranged
differently.
Amylose forms a long linear chain whereas glycogen forms many branches.
25. Carbohydrates are organic macromolecules that are made up of carbon, hydrogen, and
oxygen atoms. These atoms are combined in a ratio of
1 carbon atom : 2 hydrogen atoms : 1 oxygen atom
Carbohydrates may be simple or complex and are typically used for energy storage or as
structural molecules. Examples of carbohydrates include glucose, cellulose, starch, and
fructose.
26. ATP is a monomeric nucleotide with three consecutive phosphate groups attached rather than
one. These phosphate groups are joined by high energy phosphate-to-oxygen-to-phosphate
covalent bonds that can provide energy to activities in the cell that need energy.
NADH is a dinucleotide molecule that can store energy obtained from the breakdown of food
molecules. This energy will later be transferred to a series of molecules to synthesize more ATP
when cells need it.
27. Carbon atoms have four electrons in their outer shells, and all four are available for bonding.
Carbon can share these electrons in single bonds with up to four other atoms.
Alternatively, carbon can form double bonds with up to two other atoms by sharing two electrons
with each. Or, carbon can instead form a combination of double and single bonds, so long as it
donates no more than four electrons.
As a result of carbon's ability to bond with itself, carbon atoms can form chain-shaped or ring-
shaped molecules. The backbones of carbon molecules can be of any size and may contain from
one carbon atom to thousands of carbon atoms.
28. Proteins also serve as enzymes to control the rate of reactions and regulate cellular
activity. Enzymes are able to influence reactions as a result of their shape. Cells, in turn, can
control enzymatic activity by altering the enzyme's shape.
29. Carbon atoms have four electrons in their outer shells, and all four are available for bonding.
Carbon can share these electrons in single bonds with up to four other atoms to form very stable
structures. Alternatively, carbon can form double bonds with up to two other atoms by sharing
two electrons with each. Carbon can also form a combination of double and single bonds, as long
as no more than four electrons are donated.
30. Most solids are more dense than their liquid forms. Ice, however, is unique in that it is less
dense than liquid water and is able to float on surfaces of bodies of water, such as lakes and
oceans.
When ice forms on the surfaces of lakes and oceans, it serves as a layer of insulation. This
prevents the water bodies from freezing solid and also protects organisms, such as fish, that live
within them.