Chapter 7
*FIGURE 1* Which component is the collagen fiber of the extracellular matrix?
A
*FIGURE 3* Which line in the graph represents the bag with the highest initial concentration of sucrose?
A
Which of the following is true of the evolution of cell membranes?
All components of membranes evolve in response to natural selection.
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?
CO2
*FIGURE 1* Which component is cholesterol?
E
The sodium-potassium pump in animal cells requires cytoplasmic ATP to pump ions across the plasma membrane. When the proteins of the pump are first synthesized in the rough ER, what side of the ER membrane will the ATP binding site be on?
It will be on the cytoplasmic side of the ER.
Which of the following membrane activities require energy from ATP hydrolysis?
Na+ ions moving out of a mammalian cell bathed in physiological saline
Which of the following statements correctly describes the normal tonicity conditions for functioning plant and animal cells?
The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.
When a plant cell, such as one from a peony stem, is submerged in a very hypotonic solution, what is likely to occur?
The cell will become turgid.
A patient has had a serious accident and lost a lot of blood. In an attempt to replenish body fluids, distilled water-equal to the volume of blood lost-is transferred directly into one of his veins. What will be the most probable result of this transfusion?
The patient's red blood cells will swell because the blood fluid has become hypotonic compared to the cells.
Cell membranes are asymmetrical. Which of the following is the most likely explanation?
The two sides of a cell membrane face different environments and carry out different functions.
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?
Water will leave the cells, causing them to shrivel and collapse.
The cell membranes of Antarctic ice fish might have which of the following adaptations?
a high percentage of polyunsaturated fatty acids
n order for a protein to be an integral membrane protein it would have to be
amphipathic, with at least one hydrophobic region.
The movement of potassium into an animal cell requires
an energy source such as ATP.
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?
by increasing the percentage of unsaturated phospholipids in the membrane
In a paramecium, cell surface integral membrane proteins are synthesized
by ribosomes bound to the rough endoplasmic reticulum.
In which of the following would there be the greatest need for osmoregulation?
cells of a tidepool animal such as an anemone
The sodium-potassium pump is called an electrogenic pump because it
contributes to the membrane potential.
Ions diffuse across membranes through specific ion channels
down their electrochemical gradients.
The presence of cholesterol in the plasma membranes of some animals
enables the membrane to stay fluid more easily when cell temperature drops.
Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a 0.15 M salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are
hypertonic to fresh water but hypotonic to the salt solution.
When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are
integral proteins.
*FIGURE 2* Initially, in terms of tonicity, the solution in side A with respect to that in side B is
isotonic.
Water passes quickly through cell membranes because
it moves through aquaporins in the membrane.
A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in
lysosomes.
What is the voltage across a membrane called?
membrane potential
Which of these are not embedded in the hydrophobic portion of the lipid bilayer at all?
peripheral proteins
White blood cells engulf bacteria through what process?
phagocytosis
The difference between pinocytosis and receptor-mediated endocytosis is that
pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.
The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes is
to mediate cell-to-cell recognition.
*FIGURE 1* Which component is a glycolipid?
B
*FIGURE 3* Which line or lines in the graph represent(s) bags that contain a solution that is hypertonic at 50 minutes?
B
*FIGURE 1* Which component is a microfilament of the cytoskeleton?
C
*FIGURE 3* Which line in the graph represents the bag that contained a solution isotonic to the 0.6 M solution at the beginning of the experiment?
C
Which of the following statements is correct about diffusion?
It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?
The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
*FIGURE 2* After the system reaches equilibrium, what changes are observed?
The water level is higher in side A than in side B.
According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?
They can move laterally along the plane of the membrane.
Which of the following would increase the electrochemical potential across a membrane?
a proton pump
The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Phosphate import depends on a pH gradient across the membrane-more acidic outside the cell than inside the cell. Phosphate transport is an example of
cotransport.
Singer and Nicolson's fluid mosaic model of the membrane proposed that
membranes consist of protein molecules embedded in a fluid bilayer of phospholipids.
An organism with a cell wall would most likely be unable to take in materials through
phagocytosis.
Which of the following types of molecules are the major structural components of the cell membrane?
phospholipids and proteins
You are working on a team that is designing a new drug. In order for this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells?
similarity of the drug molecule to other molecules transported by the target cells
What kinds of molecules pass through a cell membrane most easily?
small and hydrophobic
When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that
the hydrophobic interactions that hold the membrane together are weakest at this point.