The attraction between two oppositely charged ions is called a/an

1. covalent bond
2. polar bond
3. ionic bond

c. ionic bond

Electrons are subatomic particles that determine the chemical reactions and have a

1. neutral charge
2. positive charge
3. negative charge

c. negative charge

Which of these bonds is strong and difficult to break?

1. Hydrogen bond
2. Covalent bond
3. Ionic bond

b. Covalent bond

Which bonds are created during the formation of the primary structure of a protein?

1. peptide bonds
2. hydrogen bonds
3. disulfide bonds

a. peptide bonds

The relationship between dehydration reactions and hydrolysis is best explained by which of the following?

1. Dehydration reactions assemble polymers, and hydrolysis reactions break down polymers.
2. Dehydration reactions eliminate water from lipid membranes, and hydrolysis makes lipid membranes water permeable.
3. Dehydration reactions can occur only after hydrolysis.

1. Dehydration reactions assemble polymers, and hydrolysis reactions break down polymers.

The tertiary structure of a protein is the

1. bonding together of several polypeptide chains by weak bonds.
2. order in which amino acids are joined in a polypeptide chain.
3. unique three-dimensional shape of the fully folded polypeptide.

1. unique three-dimensional shape of the fully folded polypeptide.

Which is the polysaccharide that has the most branches?

1. cellulose
2. chitin
3. glycogen
4. amylose

c. glycogen

Celery is rich in a type of glucose molecule that cannot be digested by humans. Which is the polysaccharide that is found in celery?

1. cellulose
2. chitin
3. glycogen
4. amylose

1. cellulose

Water is a/an ____________molecule

1. non polar
2. polar
3. ionic

b. polar

Molecules that have an affinity for water are referred to as

1. hydrophilic
2. hydrophobic
3. neutrophilic

1. hydrophilic

The organelle that is specialized in synthesizing sugar using certain pigments such as chlorophyll is the

1. mitochondria.
2. ribosome.
3. vacuole.
4. chloroplast.

d. chloroplast

The shape and structure of the cell is maintained by the

1. endoplasmic reticulum.
2. nucleus.
3. microtubules and microfilaments.

c. microtubules and microfilaments

The organelle that produces hydrogen peroxide, and digests other toxic metabolic byproducts is the

1. ribosomes.
2. mitochondria.
3. peroxisome.
4. nucleus.

c. peroxisome

Small molecules such as ions can move from one cell to another via

1. mitochondria.
2. gap junction.
3. tight junctions.
4. desmosomes.

b. gap junction

Which of the following statements is correct about diffusion?

1. It requires an expenditure of energy by the cell.
2. It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
3. It is an active process in which molecules move from a region of lower concentration to one of higher concentration.

b. It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.

Ions diffuse across membranes through specific ion channels

1. down their chemical gradients.
2. down their concentration gradients
3. down their electrochemical gradients.

c. down their electrochemical gradients.

The variation in charge across the plasma membrane is called

1. membrane potential
2. electro-chemical gradient
3. diffusion

a. membrane potential

Which of the following types of molecules are the major structural components of the cell membrane?

1. phospholipids and cellulose
2. nucleic acids and proteins
3. phospholipids and proteins
4. glycoproteins and cholesterol

c. phospholipids and proteins

A protein that spans the phospholipid bilayer one or more times is a

1. transmembrane protein.
2. peripheral protein.
3. glycoprotein.

a. transmembrane protein

How will brief heating (to 95°C) affect macromolecular structures in aqueous solution?

1. DNA duplexes will unwind and separate.
2. Proteins will unfold (denature).
3. Starch will hydrolyze into monomeric sugars.
4. Proteins will hydrolyze into amino acids.
5. DNA duplexes will unwind and separate, and proteins will unfold (denature).

e. DNA duplexes will unwind and separate, and proteins will unfold (denature)

Which of the following effects is produced by the high surface tension of water?

1. Lakes don't freeze solid in winter, despite low temperatures.
2. A water strider can walk across the surface of a small pond.
3. Organisms resist temperature changes, although they give off heat due to chemical reactions.
4. Evaporation of sweat from the skin helps to keep people from overheating.
5. Water flows upward from the roots to the leaves in plants.

b. A water strider can walk across the surface of a small pond

A molecule with the chemical formula C6H12O6 is probably a:

1. Carbohydrate
2. Lipid
3. Monosaccharide
4. Carbohydrate and lipid only
5. Carbohydrate and monosaccharide only

e. Carbohydrate and monosaccharide only

Which two functional groups are always found in amino acids?

1. Ketone and methyl
2. Carbonyl and amino
3. Carboxyl and amino
4. Amino and sulfhydryl
5. Hydroxyl and carboxyl

c. Carboxyl and amino

If one strand of a DNA molecule has the sequence of bases 5'ATTGCA3', the other complementary strand would have the sequence:

1. 5'TAACGT3'.
2. 5'TGCAAT3'.
3. 5'UAACGU3'.
4. 3'UAACGU5'.
5. 5'UGCAAU3'.

b. 5'TGCAAT3'.

Which functional group is not present in this molecule?

1. Carboxyl
2. Sulfhydryl
3. Hydroxyl
4. Amino

b. Sulfhydryl

The element present in all organic molecules is:

1. Hydrogen
2. Oxygen
3. Carbon
4. Nitrogen
5. Phosphorus

c. carbon

Which of the following statements is true about buffer solutions?

1. They maintain a constant pH when bases are added to them but not when acids are added to them.
2. They maintain a constant pH when acids are added to them but not when bases are added to them.
3. They maintain a relatively constant pH of approximately 7 when either acids or bases are added to them.
4. They maintain a relatively constant pH when either acids or bases are added to them.
5. They are found only in living systems and biological fluids.

d. They maintain a relatively constant pH when either acids or bases are added to them.

How many electron pairs does carbon share in order to complete its valence shell?

1. 1
2. 2
3. 3
4. 4
5. 8

d. 4

A carbon atom is most likely to form what kind of bond(s) with other atoms?

1. Ionic
2. Hydrogen
3. Covalent
4. Covalent bonds and hydrogen bonds
5. Ionic bonds, covalent bonds, and hydrogen bonds

c. covalent

Which of the following statements is true for the class of biological molecules known as lipids?

1. They are insoluble in water.
2. They are made from glycerol, fatty acids, and phosphate.
3. They contain less energy than proteins and carbohydrates.
4. They are made by dehydration reactions.
5. They contain nitrogen

a. They are insoluble in water

At which level of protein structure are interactions between the side chains (R groups) most important?

1. Primary
2. Secondary
3. Tertiary
4. Quaternary
5. All of the above

c. tertiary

Why are hydrocarbons insoluble in water?

1. The majority of their bonds are polar covalent carbon-to-hydrogen linkages.
2. The majority of their bonds are nonpolar covalent carbon-to-hydrogen linkages.
3. They are hydrophilic.
4. They exhibit considerable molecular complexity and diversity.
5. They are lighter than water.

b. The majority of their bonds are nonpolar covalent carbon-to-hydrogen linkages

A covalent chemical bond is one in which:

1. Electrons are removed from one atom and transferred to another atom so that the two atoms become oppositely charged.
2. Protons and neutrons are shared by two atoms so as to satisfy the requirements of both atoms.
3. Outer-shell electrons of two atoms are shared so as to satisfactorily fill the outer electron shells of both atoms.
4. Outer-shell electrons of one atom are transferred to fill the inner electron shell of another atom.
5. An electron occupies a hybrid orbital located between the nuclei of two atoms

c. Outer-shell electrons of two atoms are shared so as to satisfactorily fill the outer electron shells of both atoms.

Which of the following best summarizes the relationship between dehydration reactions and hydrolysis?

1. Dehydration reactions assemble polymers, and hydrolysis reactions break down polymers.
2. Dehydration reactions eliminate water from lipid membranes, and hydrolysis makes lipid membranes water permeable.
3. Dehydration reactions can occur only after hydrolysis.
4. Hydrolysis creates monomers, and dehydration reactions break down polymers.
5. Dehydration reactions ionize water molecules and add hydroxyl groups to polymers; hydrolysis reactions release hydroxyl groups from polymers.

a. Dehydration reactions assemble polymers, and hydrolysis reactions break down polymers.

What maintains the secondary structure of a protein?

1. Peptide bonds
2. Hydrogen bonds between the amino group of one peptide bond and the carboxyl group of another peptide bond
3. Disulfide bonds
4. Hydrophobic interactions
5. Hydrogen bonds between the R groups

b. Hydrogen bonds between the amino group of one peptide bond and the carboxyl group of another peptide bond

Which of the following explains most specifically the attraction of water molecules to one another?

1. Nonpolar covalent bond
2. Polar covalent bond
3. Ionic bond
4. Hydrogen bond
5. Hydrophobic interaction

d. hydrogen bonds

If a DNA sample were composed of 10% thymine, what would be the percentage of guanine?

1. 10
2. 20
3. 40
4. 80

c. 40

Hydrophobic substances such as vegetable oil are:

1. Nonpolar substances that repel water molecules.
2. Nonpolar substances that have an attraction for water molecules.
3. Polar substances that repel water molecules.
4. Polar substances that have an affinity for water.
5. Charged molecules that hydrogen-bond with water molecules.

a. Nonpolar substances that repel water molecules.

What results from an unequal sharing of electrons between atoms?

1. A nonpolar covalent bond
2. A polar covalent bond
3. An ionic bond
4. A hydrogen bond
5. A hydrophobic interaction

b. A polar covalent bond

Which of the following is a hydrophobic material?

1. Paper
2. Table salt
3. Wax
4. Sugar
5. Pasta

c. Wax

Why does ice float in liquid water?

1. The high surface tension of liquid water keeps the ice on top.
2. The ionic bonds between the molecules in ice prevent the ice from sinking.
3. Ice always has air bubbles that keep it afloat.
4. Hydrogen bonds stabilize and keep the molecules of ice farther apart than the water molecules of liquid water.
5. The crystalline lattice of ice causes it to be denser than liquid water.

d. Hydrogen bonds stabilize and keep the molecules of ice farther apart than the water molecules of liquid water.

Which of the following descriptions best fits the class of molecules known as nucleotides?

1. A nitrogenous base and a phosphate group
2. A nitrogenous base and a pentose sugar
3. A nitrogenous base, a phosphate group, and a pentose sugar
4. A phosphate group and an adenine or uracil
5. A pentose sugar and a purine or pyrimidine

c. A nitrogenous base, a phosphate group, and a pentose sugar

Which of the following is the best description of a control for an experiment?

1. The control group is kept in an unchanging environment.
2. The control is left alone by the experimenters.
3. The control group is matched with the experimental group except for the one experimental variable.
4. The control group is exposed to only one variable rather than several.
5. Only the experimental group is tested or measured.

c. The control group is matched with the experimental group except for the one experimental variable.

Which type of bond must be broken for water to vaporize?

1. Ionic bonds
2. Both hydrogen bonds and ionic bonds
3. Polar covalent bonds
4. Hydrogen bonds
5. Both polar covalent bonds and hydrogen bonds

d. hydrogen bonds

Which functional group is characteristic of alcohols?

1. A
2. B
3. C
4. D
5. E

a. A

About 25 of the 92 natural elements are known to be essential to life. Which four of these 25 elements make up approximately 96% of living matter

1. carbon, sodium, hydrogen, nitrogen
2. carbon, oxygen, phosphorus, hydrogen
3. oxygen, hydrogen, calcium, nitrogen
4. carbon, hydrogen, nitrogen, oxygen
5. carbon, oxygen, nitrogen, calcium

d. carbon, hydrogen, nitrogen, oxygen

Which functional group(s) shown above is (are) present in all amino acids?

1. A and B
2. B and D
3. C only
4. D only
5. C and D

e. C and D

Humans can digest starch, but not cellulose because:

1. The monomer of starch is glucose, while the monomer of cellulose is galactose.
2. Humans have enzymes that can hydrolyze the β glycosidic linkages of starch, but not the α glycosidic linkages of cellulose.
3. Humans have enzymes that can hydrolyze the α glycosidic linkages of starch, but not the β glycosidic linkages of cellulose.
4. Humans harbor starch-digesting bacteria in the digestive tract.
5. The monomer of starch is glucose, while the monomer of cellulose is glucose with a nitrogen-containing group.

c. Humans have enzymes that can hydrolyze the α glycosidic linkages of starch, but not the β glycosidic linkages of cellulose.

What is the structural feature that allows DNA to replicate?

1. Sugar-phosphate backbone
2. Complementary pairing of the nitrogenous bases
3. Disulfide bonding (bridging) of the two helixes
4. Twisting of the molecule to form an α helix
5. Three-component structure of the nucleotides

b. Complementary pairing of the nitrogenous bases

The following question is based on the 15 molecules illustrated in Figure 5.8. Each molecule may be used once, more than once, or not at all.

Which molecule is glycerol?

1. 1
2. 6
3. 10
4. 14
5. 15

c. 10

What is the term used for a protein molecule that assists in the proper folding of other proteins?

1. Tertiary protein
2. Chaperonin
3. Enzyme protein
4. Renaturing protein
5. Denaturing protein

b. Chaperonin

The tertiary structure of a protein is the:

1. Bonding together of several polypeptide chains by weak bonds.
2. Order in which amino acids are joined in a polypeptide chain.
3. Unique three-dimensional shape of the fully folded polypeptide.
4. Organization of a polypeptide chain into an α helix or β pleated sheet.
5. Overall protein structure resulting from the aggregation of two or more polypeptide subunits.

c. Unique three-dimensional shape of the fully folded polypeptide

The partial negative charge in a molecule of water occurs because:

1. The oxygen atom acquires an additional electron.
2. The electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus.
3. The oxygen atom has two pairs of electrons in its valence shell that are not neutralized by hydrogen atoms.
4. The oxygen atom forms hybrid orbitals that distribute electrons unequally around the oxygen nucleus.
5. One of the hydrogen atoms donates an electron to the oxygen atom.

b. The electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus.

Which bonds are created during the formation of the primary structure of a protein?

1. Peptide bonds
2. Hydrogen bonds
3. Disulfide bonds
4. Phosphodiester bonds
5. Peptide bonds, hydrogen bonds, and disulfide bonds

a. Peptide Bonds

The method of scientific inquiry that describes natural structures and processes as accurately as possible through careful observation and the analysis of data is known as:

1. Hypothesis-based science
2. Discovery science
3. Experimental science
4. Quantitative science
5. Qualitative science

b. Discovery Science

When applying the process of science, which of these is tested?

1. A question
2. A result
3. An observation
4. A prediction
5. A hypothesis

e. A Hypothesis

There are 20 different amino acids. What makes one amino acid different from another?

1. Different side chains (R groups) attached to a carboxyl carbon
2. Different side chains (R groups) attached to the amino groups
3. Different side chains (R groups) attached to an α carbon
4. Different structural and optical isomers
5. Different asymmetric carbons

c. Different side chains (R groups) attached to an α carbon

Which bond or interaction would be difficult to disrupt when compounds are put into water?

1. Covalent bond
2. Hydrogen bond
3. Van der Waals interaction
4. Ionic bond
5. Either covalent bonds or ionic bonds

a. Covalent bond

The following question is based on the 15 molecules illustrated in Figure 5.8. Each molecule may be used once, more than once, or not at all.

Which molecule is a saturated fatty acid

1. 1
2. 5
3. 6
4. 8
5. 9

e. 9

Which animal cell organelle contains enzymes that transfer hydrogen from various substrates to oxygen?

1. Lysosome
2. Vacuole
3. Mitochondrion
4. Golgi apparatus
5. Peroxisome

e. Peroxisome

Which of the following contains hydrolytic enzymes?

1. Lysosome
2. Vacuole
3. Mitochondrion
4. Golgi apparatus
5. Peroxisome

a. Lysosome

Thylakoids, DNA, and ribosomes are all components found in:

1. Vacuoles
2. Chloroplasts
3. Mitochondria
4. Lysosomes
5. Nuclei

b. Chloroplasts

Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

1. The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
2. Unsaturated fatty acids have a higher cholesterol content and therefore more cholesterol in membranes.
3. Unsaturated fatty acids are more polar than saturated fatty acids.
4. The double bonds block interaction among the hydrophilic head groups of the lipids.
5. The double bonds result in shorter fatty acid tails and thinner membranes.

a.The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly

Which organelle is the primary site of ATP synthesis in eukaryotic cells?

1. Lysosome
2. Vacuole
3. Mitochondrion
4. Golgi apparatus
5. Peroxisome

c. Mitochondrion

Which of the following produces and modifies polysaccharides that will be secrete

1. Lysosome
2. Vacuole
3. Mitochondrion
4. Golgi apparatus
5. Peroxisome

d.Golgi apparatus

What kinds of molecules pass through a cell membrane most easily?

1. Large and hydrophobic
2. Small and hydrophobic
3. Large polar
4. Ionic
5. Monosaccharides such as glucose

b.Small and hydrophobic

White blood cells engulf bacteria through what process?

1. Exocytosis
2. Phagocytosis
3. Pinocytosis
4. Osmosis
5. Receptor-mediated exocytosis

b. Phagocytosis

A protein that spans the phospholipid bilayer one or more times is:

1. A transmembrane protein
2. An integral protein
3. A peripheral protein
4. An integrin
5. A glycoprotein

a. A transmembrane protein

Prokaryotes are classified as belonging to two different domains. What are the domains?

1. Bacteria and eukarya
2. Bacteria and archaea
3. Archaea and protista
4. Bacteria and protista
5. Bacteria and fungi

b.Bacteria and archaea

Large numbers of ribosomes are present in cells that specialize in producing which of the following molecules?

1. Lipids
2. Glycogen
3. Proteins
4. Cellulose
5. Nucleic acids

c.Proteins

Which of the following types of molecules are the major structural components of the cell membrane?

1. Phospholipids and cellulose
2. Nucleic acids and proteins
3. Phospholipids and proteins
4. Proteins and cellulose
5. Glycoproteins and cholesterol

c.Phospholipids and proteins

Which structure is the site of the synthesis of proteins that may be exported from the cell?

1. Rough ER
2. Lysosomes
3. Plasmodesmata
4. Golgi vesicles
5. Free cytoplasmic ribosomes

a.Rough ER

Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?

1. CO2
2. An amino acid
3. Glucose
4. K+
5. Starch

a. CO2

All of the following are part of a prokaryotic cell except

1. DNA
2. A cell wall.
3. A plasma membrane
4. Ribosomes
5. An endoplasmic reticulum

e.An endoplasmic reticulum

In order for a protein to be an integral membrane protein it would have to be:

1. Hydrophilic
2. Hydrophobic
3. Amphipathic, with at least one hydrophobic region
4. Completely covered with phospholipids
5. Exposed on only one surface of the membrane

c.Amphipathic, with at least one hydrophobic region

The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes is:

1. To facilitate diffusion of molecules down their concentration gradients.
2. To actively transport molecules against their concentration gradients.
3. To maintain the integrity of a fluid mosaic membrane.
4. To maintain membrane fluidity at low temperatures.
5. To mediate cell-to-cell recognition.

e. To mediate cell-to-cell recognition.

A cell with a predominance of free ribosomes is most likely:

1. Producing primarily proteins for secretion.
2. Producing primarily cytoplasmic proteins.
3. Constructing an extensive cell wall or extracellular matrix.
4. Digesting large food particles.
5. Enlarging its vacuole.

b.Producing primarily cytoplasmic proteins.

A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in:

1. Peroxisomes
2. Lysosomes
3. Golgi vesicles
4. Vacuoles
5. Secretory vesicles

b.Lysosomes

The difference between pinocytosis and receptor-mediated endocytosis is that:

1. Pinocytosis brings only water molecules into the cell, but receptor-mediated endocytosis brings in other molecules as well.
2. Pinocytosis increases the surface area of the plasma membrane whereas receptor-mediated endocytosis decreases the plasma membrane surface area.
3. Pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.
4. Pinocytosis requires cellular energy, but receptor-mediated endocytosis does not.
5. Pinocytosis can concentrate substances from the extracellular fluid, but receptor-mediated endocytosis cannot.

c.Pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

1. It is a peripheral membrane protein.
2. It exhibits a specificity for a particular type of molecule.
3. It requires the expenditure of cellular energy to function.
4. It works against diffusion.
5. It has few, if any, hydrophobic amino acids.

b.It exhibits a specificity for a particular type of molecule.

Which plant cell organelle contains its own DNA and ribosomes?

1. Glyoxysome
2. Vacuole
3. Mitochondrion
4. Golgi apparatus
5. Peroxisome

c.Mitochondrion

In a liver cell detoxifying alcohol and some other poisons, the enzymes of the peroxisome remove hydrogen from these molecules and:

1. Combine the hydrogen with water molecules to generate hydrogen peroxide.
2. Use the hydrogen to break down hydrogen peroxide.
3. Transfer the hydrogen to the mitochondria.
4. Transfer the hydrogen to oxygen molecules to generate hydrogen peroxide.

d.Transfer the hydrogen to oxygen molecules to generate hydrogen peroxide.

Signals between the ECM and the cytoskeleton may be transmitted by:

1. Fibronectin
2. Proteoglycans
3. Integrins
4. Collagen
5. Middle lamella

c. Integrins

What is the voltage across a membrane called?

1. Water potential
2. Chemical gradient
3. Membrane potential
4. Osmotic potential
5. Electrochemical gradient

c.Membrane potential

Ions diffuse across membranes through specific ion channels:

1. Down their chemical gradients.
2. Down their concentration gradients.
3. Down the electrical gradients.
4. Down their electrochemical gradients.
5. Down the osmotic potential gradients.

d.Down their electrochemical gradients.

A primary objective of cell fractionation is to:

1. View the structure of cell membranes.
2. Sort cells based on their size and weight.
3. Determine the size of various organelles.
4. Separate the major organelles so that their particular functions can be determined.
5. Separate lipid-soluble from water-soluble molecules.

d.Separate the major organelles so that their particular functions can be determined.

According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?

1. They can move laterally along the plane of the membrane.
2. They frequently flip-flop from one side of the membrane to the other.
3. They occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane.
4. They are free to depart from the membrane and dissolve in the surrounding solution.
5. They have hydrophilic tails in the interior of the membrane.

a.They can move laterally along the plane of the membrane.

Which type of organelle or structure is primarily involved in the synthesis of oils, phospholipids, and steroids?

1. Ribosome
2. Lysosome
3. Smooth endoplasmic reticulum
4. Mitochondrion
5. Contractile vacuole

c.Smooth endoplasmic reticulum

Mammalian blood contains the equivalent of 0.15 M NaCl. Seawater contains the equivalent of 0.45 M NaCl. What will happen if red blood cells are transferred to seawater?

1. Water will leave the cells, causing them to shrivel and collapse.
2. NaCl will be exported from the red blood cells by facilitated diffusion.
3. The blood cells will take up water, swell, and eventually burst.
4. NaCl will passively diffuse into the red blood cells.
5. The blood cells will expend ATP for active transport of NaCl into the cytoplasm.

a.Water will leave the cells, causing them to shrivel and collapse.

Which of the following is true of integral membrane proteins?

1. They lack tertiary structure.
2. They are loosely bound to the surface of the bilayer.
3. They are usually transmembrane proteins.
4. They are not mobile within the bilayer.
5. They serve only a structural role in membranes.

c.They are usually transmembrane proteins.

Which of these are not embedded in the hydrophobic portion of the lipid bilayer at all?

1. Transmembrane proteins
2. Integral proteins
3. Peripheral proteins
4. Integrins
5. Glycoproteins

c.Peripheral proteins

Which of the following statements is correct about diffusion?

1. It is very rapid over long distances.
2. It requires an expenditure of energy by the cell.
3. It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
4. It is an active process in which molecules move from a region of lower concentration to one of higher concentration.
5. It requires integral proteins in the cell membrane.

c.It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.

The presence of cholesterol in the plasma membranes of some animals:

1. Enables the membrane to stay fluid more easily when cell temperature drops.
2. Enables the animal to remove hydrogen atoms from saturated phospholipids.
3. Enables the animal to add hydrogen atoms to unsaturated phospholipids.
4. Makes the membrane less flexible, allowing it to sustain greater pressure from within the cell.
5. Makes the animal more susceptible to circulatory disorders.

a. Enables the membrane to stay fluid more easily when cell temperature drops.

Movement of vesicles within the cell depends on what cellular structures?

1. Microtubules and motor proteins
2. Actin filaments and microtubules
3. Actin filaments and ribosomes
4. Centrioles and motor proteins
5. Actin filaments and motor proteins

a.Microtubules and motor proteins

In a plant cell, DNA may be found:

1. Only in the nucleus.
2. Only in the nucleus and mitochondria.
3. Only in the nucleus and chloroplasts.
4. In the nucleus, mitochondria, and chloroplasts.
5. In the nucleus, mitochondria, chloroplasts, and peroxisomes.

d.In the nucleus, mitochondria, and chloroplasts.

Ions can travel directly from the cytoplasm of one animal cell to the cytoplasm of an adjacent cell through:

1. Plasmodesmata
2. Intermediate filaments
3. Tight junctions
4. Desmosomes
5. Gap junctions

e.Gap junctions

Water passes quickly through cell membranes because:

1. The bilayer is hydrophilic.
2. It moves through hydrophobic channels.
3. Water movement is tied to ATP hydrolysis.
4. It is a small, polar, charged molecule.
5. It moves through aquaporins in the membrane.

e.It moves through aquaporins in the membrane.

Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. As a result, these lipid rafts:

1. Are more fluid than the surrounding membrane.
2. Are more rigid than the surrounding membrane.
3. Are able to flip from inside to outside.
4. Detach from the plasma membrane and clog arteries.
5. Have higher rates of lateral diffusion of lipids and proteins into and out of the lipid rafts.

b.Are more rigid than the surrounding membrane.

In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis?

1. On the outside of vesicles
2. On the inside surface of the cell membrane
3. On the inside surface of the vesicle
4. On the outer surface of the nucleus
5. On the ER

c.On the inside surface of the vesicle