Who was/were the first to propose that cell membranes are phospholipid bilayers?
A) I. Langmuir
B) H. Davson and J. Danielli
C) E. Gorter and F. Grendel
D) S. Singer and G. Nicolson
E) C. Overton
E. Gorter and F. Grendel
Which of the following types of molecules are the major structural components of the cell membrane?
A) phospholipids and cellulose
B) phospholipids and proteins
C) nucleic acids and proteins
D) glycoproteins and cholesterol
E) proteins and cellulose
phospholipids and proteins
The presence of cholesterol in the plasma membranes of some animals
A) enables the membrane to stay fluid more easily when cell temperature drops.
B) makes the membrane less flexible, allowing it to sustain greater pressure from within the cell.
C) enables the animal to remove hydrogen atoms from saturated phospholipids.
D) makes the animal more susceptible to circulatory disorders.
E) enables the animal to add hydrogen atoms to unsaturated phospholipids.
enables the membrane to stay fluid more easily when cell temperature drops.
According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?
A) They occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of
B) They are free to depart from the membrane and dissolve in the surrounding solution.
C) They have hydrophilic tails in the interior of the membrane.
D) They can move laterally along the planeof the membrane.
E) They frequently flip-flop from one side of the membrane to the other.
They can move laterally along the planeof the membrane.
Which of the following is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold?
A) by using active transport
B) by increasing the percentage of unsaturated phospholipids in the membrane
C) by decreasing the number of hydrophobic proteins in the membrane
D) by cotransport of glucose and hydrogen
E) by increasing the percentage of cholesterol molecules in the membrane
by increasing the percentage of unsaturated phospholipids in the membrane
In order for a protein to be an integral membrane protein it would have to be
C) amphipathic, with at least one hydrophobic region.
D) completely covered with phospholipids.
E) exposed on only one surface of the membrane.
amphipathic, with at least one hydrophobic region.
When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of of freeze fractured membranes, the bumps seen on the fractured surface of the membrane are:
A) cholesterol molecules.
D) integral proteins.
E) peripheral proteins.
Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?
A) The double bonds result in shorter fatty acid tails and thinner membranes.
B) The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
C) The double bonds block interaction among the hydrophilic head groups of the lipids.
D) Unsaturated fatty acids are more polar than saturated fatty acids.
E) Unsaturated fatty acids have a higher cholesterol content and therefore more cholesterol in membranes.
The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
Which of the following is true of integral membrane proteins?
A) They are usually transmembrane proteins.
B) They are loosely bound to the surface of the bilayer.
C) They lack tertiary structure.
D) They serve only a structural role in membranes.
E) They are not mobile within the bilayer
They are usually transmembrane proteins
The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes is
A) to maintain membrane fluidity at low temperatures.
B) to facilitate diffusion of molecules down their concentration gradients.
C) to actively transport molecules against their concentration gradients.
D) to maintain the integrity of a fluid mosaic membrane.
E) to mediate cell-to-cell recognition.
to mediate cell-to-cell recognition
An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function?
A) attaching to the cytoskeleton
B) cell-cell recognition
C) transporting ions against an electrochemical gradient
D) maintaining fluidity of the phospholipid bilayer
E) establishing the diffusion barrier to charged molecules
A protein that spans the phospholipid bilayer one or more times is
A) a glycoprotein.
B) a transmembrane protein.
C) an integrin.
D) an integral protein.
E) a peripheral protein.
a transmembrane protein
Which of these are not embedded in the hydrophobic portion of the lipid bilayer at all?
B) transmembrane proteins
C) peripheral proteins
D) integral proteins
The cell membranes of Antarctic ice fish might have which of the following adaptations?
A) a high percentage of polyunsaturated fatty acids
B) very long chain fatty acids
C) a higher percentage of trans-fatty acids
D) no cholesterol
E) branched isoprenoid lipids
a high percentage of polyunsaturated fatty acids
In a paramecium, cell surface integral membrane proteins are synthesized
A) by ribosomes bound to the inner surface of the plasma membrane.
B) by ribosomes in the Golgi vesicles.
C) by ribosomes in the nucleus.
D) by ribosomes bound to the rough endoplasmic reticulum.
E) in the cytoplasm by free ribosomes.
by ribosomes bound to the rough endoplasmic reticulum
The formulation of a model for a structure or for a process serves which of the following purposes?
A) It serves as a data point among results.
B) It asks a scientific question.
C) It functions as a testable hypothesis.
D) It records observations.
E) It can only be arrived at after years of experimentation.
It functions as a testable hypothesis
Cell membranes are asymmetrical. Which of the following is the most likely explanation?
A) Proteins can only be associated with the cell membranes on the cytoplasmic side.
B) Cell membranes communicate signals from one organism to another.
C) The cell membrane forms a border between one cell and another in tightly packed tissues
such as epithelium.
D) The "innemess" and "outemess" of membrane surfaces are predetermined by genes.
E) The two sides of a cell membrane face different environments and carry out different
The two sides of a cell membrane face different environments and carry out different
Which of the following is true of the evolution of cell membranes?
A) Cell membranes cannot evolve if the membrane proteins do not.
B) An individual organism selects its preferred type of cell membrane for particular functions. C) The evolution of cell membranes is driven by the evolution of glycoproteins and glycolipids.
D) All components of membranes evolve in response to natural selection.
E) Cell membranes have stopped evolving now that they are fluid mosaics
All components of membranes evolve in response to natural selection
Why are lipids and proteins free to move laterally in membranes?
A) The interior of the membrane is filled with liquid water.
B) Lipids and proteins repulse each other in the membrane.
C) Molecules such as cellulose can pull them in various directions.
D) Hydrophilic portions of the lipids are in the interior of the membrane.
E) There are only weak hydrophobic interactions in the interior of the membrane
There are only weak hydrophobic interactions in the interior of the membrane
What kinds of molecules pass through a cell membrane most easily?
A) large polar
B) large and hydrophobic
C) monosaccharides such as glucose
E) small and hydrophobic
small and hydrophobic
Which of the following is a characteristic feature of a carrier protein in a plasma membrane?
A) It is a peripheral membrane protein.
B) It has few, if any, hydrophobic amino acids.
C) It requires the expenditure of cellular energy to function.
D) It works against diffusion.
E) It exhibits a specificity for a particular type of molecule.
It exhibits a specificity for a particular type of molecule
Nitrous oxide gas molecules diffusing across a cell's plasma membrane is an example of
A) diffusion across the lipid bilayer.
C) facilitated diffusion.
D) active transport.
diffusion across the lipid bilayer
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?
D) an amino acid
Which of the following statements is correct about diffusion?
A) It is an active process in which molecules move from a region of lower concentration to one of higher concentration.
B) It requires an expenditure of energy by the cell.
C) It is very rapid over long distances.
D) It requires integral proteins in the cell membrane.
E) It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
Water passes quickly through cell membranes because
A) it moves through hydrophobic channels.
B) it is a small, polar, charged molecule.
C) water movement is tied to ATP hydrolysis.
D) the bilayer is hydrophilic.
E) it moves through aquaporins in the membrane.
it moves through aquaporins in the membrane.
Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?
A) The animal cell is in a hypertonic solution, and the plant cell is in an isotonic solution.
B) The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.
C) The animal cell is in an isotonic solution, and the plant cell is in a hypertonic solution.
D) The animal cell is in a hypertonic solution, and the plant cell is in a hypotonic solution.
E) The animal cell is in a hypotonic solution, and the plant cell is in an isotonic solution
The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.
In which of the following would there be the greatest need for osmoregulation?
A) a lymphocyte before it has been taken back into lymph fluid
B) an animal connective tissue cell bathed in isotonic body fluid
C) a red blood cell surrounded by plasma
D) a plant being grown hydroponically (in a watery mixture of designated nutrients)
E) cells of a tidepool animal such as an anemone
cells of a tidepool animal such as an anemone
When a plant cell, such as one from a peony stem, is submerged in a very hypotonic solution, what is likely to occur?
A) The cell will become flaccid.
B) Plasmolysis will shrink the interior.
C) The cell membrane will lyse.
D) The cell will burst.
E) The cell will become turgid
The cell will become turgid
Which of the following membrane activities require energy from ATP hydrolysis?
A) movement of water into a cell
B) movement of carbon dioxide out of a paramecium
C) movement of glucose molecules into a bacterial cell from a medium containing a higher concentration of glucose than inside the cell
D) facilitated diffusion of chloride ions across the membrane through a chloride channel
E) Na+ ions moving out of a mammalian cell bathed in physiological saline
Na+ ions moving out of a mammalian cell bathed in physiological saline
Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. Using this information, which transport mechanism is most probably functioning in the intestinal cells?
A) facilitated diffusion
B) simple diffusion
E) active transport pumps
What is the voltage across a membrane called?
A) osmotic potential
B) chemical gradient
C) electrochemical gradient
D) water potential
E) membrane potential
In most cells, there are electrochemical gradients of many ions across the plasma membrane even though there are usually only one or two electrogenic pumps present in the membrane. The
gradients of the other ions are most likely accounted for by
A) ion channels.
B) cellular metabolic reactions that create or destroy ions.
C) carrier proteins.
D) passive diffusion across the plasma membrane.
E) cotransport proteins.
The sodium-potassium pump is called an electrogenic pump because it
A) pumps hydrogen ions out of the cell.
B) contributes to the membrane potential.
C) pumps equal quantities of N+ and K+ across the membrane.
D) is used to drive the transport of other molecules against a concentration gradient.
E) ionizes sodium and potassium atoms.
contributes to the membrane potential.
The movement of potassium into an animal cell requires
A) high cellular concentrations of potassium.
B) a potassium channel protein.
C) an energy source such as ATP.
D) low cellular concentrations of sodium.
E) a cotransport protein.
an energy source such as ATP
Ions diffuse across membranes through specific ion channels
A) down their chemical gradients.
B) down their concentration gradients.
C) down the osmotic potential gradients.
D) down their electrochemical gradients.
E) down the electrical gradients.
down their electrochemical gradients
Which of the following would increase the electrochemical potential across a membrane?
A) a proton pump
B) a potassium channel
C) a sucrose-proton cotransporter
D) both a proton pump and a potassium channel
E) a chloride channel
a proton pump
Several epidemic microbial diseases of earlier centuries incurred high death rates because they resulted in severe dehydration due to vomiting and diarrhea. Today they are usually because we have developed which of the following?
A) hydrating drinks that include high concentrations of salts and glucose
B) antibiotics against the viruses in question
C) antiviral medications that are efficient and work well with all viruses
D) intravenous feeding techniques
E) medication to prevent blood loss
hydrating drinks that include high concentrations of salts and glucose
An organism with a cell wall would most likely be unable to take in materials through
C) active transport.
D) facilitated diffusion.
White blood cells engulf bacteria through what process?
D) receptor-mediated exocytosis
Familial hypercholesterolemia is characterized by which of the following?
A) a poorly formed lipid bilayer that cannot incorporate cholesterol into cell membranes
B) defective LDL receptors on the cell membranes
C) a general lack of glycolipids in the blood cell membranes
D) poor attachment of the cholesterol to the extracellular matrix of cells
E) inhibition of the cholesterol active transport system in red blood cells
defective LDL receptors on the cell membranes
The difference between pinocytosis and receptor-mediated endocytosis is that
A) pinocytosis increases the surface area of the plasma membrane whereas receptor-mediated endocytosis decreases the plasma membrane surface area.
B) pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.
C) pinocytosis can concentrate substances from the extracellular fluid, but receptor-mediated
D) pinocytosis brings only water molecules into the cell, but receptor-mediated endocytosis brings in other molecules as well.
E) pinocytosis requires cellular energy, but receptor-mediated endocytosis does not
pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.
) In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis?
A) on the inside surface of the cell membrane
B) on the inside surface of the vesicle
C) on the outer surface of the nucleus
D) on the outside of vesicles
E) on the ER
on the inside surface of the vesicle
A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in
A) Golgi vesicles.
B) secretory vesicles.
In what way do the membranes of a eukaryotic cell vary?
A) Certain proteins are unique to each membrane.
B) Only certain membranes of the cell are selectively permeable.
C) Some membranes have hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm.
D) Only certain membranes are constructed from amphipathic molecules.
E) Phospholipids are found only in certain membranes.
Only certain membranes of the cell are selectively permeable.
Which of the following factors would tend to increase membrane fluidity?
A) a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses
B) a greater proportion of unsaturated phospholipids
C) a lower temperature
D) a relatively high protein content in the membrane
E) a greater proportion of saturated phospholipids
a greater proportion of unsaturated phospholipids