Biology test ch 6

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

CO2

Which of the following is true of osmosis?

In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.

Under what circumstances does membrane transport require energy?

whenever a solute is moved against its electrochemical gradient

Which line in the graph represents the bag with the highest initial concentration of sucrose?

A

Which of the following is most likely true of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal?

A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.

A number of systems for pumping ions across membranes are powered by ATP. Such ATP- powered pumps are often called ATPases, although they do not often hydrolyze ATP unless they are simultaneously transporting ions. Because small increases in calcium ions in the cytosol can trigger a number of different intracellular reactions, cells keep the cytosolic calcium concentration quite low under normal conditions, using ATP-powered calcium pumps. For example, muscle cells transport calcium from the cytosol into the membranous system called the sarcoplasmic reticulum (SR). If a resting muscle cell's cytosol has a free calcium ion concentration of 10-7 while the concentration in the SR is 10-2, then how is the ATPase acting?

ATPase activity must be opening a channel for the calcium ions to diffuse back into the SR along the concentration gradient.

Which line or lines in the graph represent(s) bags that contain a solution that is hypertonic at 50 minutes?

B

Which of the following is the best explanation for why cholesterol decreases the permeability of biological membranes?

Because cholesterol is amphipathic, it fits in between the phospholipids and blocks diffusion through the membrane.

In what way do the membranes of a eukaryotic cell vary?

Certain proteins are unique to each membrane.

Which component is a peripheral protein?

D

In an experiment involving planar bilayers, a solution of table salt (sodium and chloride ions in water) is added on the left side of the membrane while pure water is added on the right side. After 30 minutes the researchers test for the presence of ions on each side of the membrane. The right side tests negative for ions. What can you conclude?

Ions cannot cross planar bilayers.

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

It exhibits a specificity for a particular type of molecule.

Gramicidin is an antibiotic that increases the permeability of bacterial cell walls to inorganic ions. What is the most likely mode of action of gramicidin?

It forms a channel in the membrane.

What is the most important factor in explaining why osmosis occurs spontaneously?

It leads to an increase in entropy.

You make a phospholipid bilayer with short, saturated hydrocarbon tails. You measure the permeability of this membrane to oxygen. You then double the length of the hydrocarbon tails, and remeasure membrane permeability. You then double the length of the hydrocarbon tails again, and make a third measurement of membrane permeability. You graph membrane permeability as a function of hydrocarbon tail length. Which of the graphs below best represents the data you expect?

Negative slope

You have a planar bilayer with equal amounts of saturated and unsaturated phospholipids. After testing the permeability of this membrane to glucose, you increase the proportion of unsaturated phospholipids in the bilayer. What will happen to the membrane's permeability to glucose?

Permeability to glucose will increase.

If you mechanically shook a mixture of phospholipids and water, what would you expect to see when you observe the solution using an electron microscope?

Some lipids will have formed tiny vesicles filled with water.

You make a phospholipid bilayer with short, saturated hydrocarbon tails. You measure the permeability of this membrane to oxygen. You are going to change the length of the hydrocarbon tails and remeasure membrane permeability, but first your boss asks you to graph the data you expect if there is no effect of hydrocarbon tail length on membrane permeability (your null hypothesis). Which of the graphs below best represents the data you expect if your null hypothesis is correct?

Straight line no slope

You have just discovered an organism that lives in extremely cold environments. Which of the following would you predict to be true about the phospholipids in its membranes, compared to phospholipids in the membranes of organisms that live in warmer environments?

The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails.

A patient was involved a serious accident and lost a large quantity of blood. In an attempt to replenish body fluids, distilled water—equal to the volume of blood lost—is added to the blood directly via one of his veins. What will be the most probable result of this transfusion?

The patient's red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells.

Steroid hormones are large communication molecules that are modified cholesterol molecules. How do you think they enter a cell?

Their lipid nature probably allows them to diffuse through the plasma membrane.

Why are lipids and proteins free to move laterally in membranes?

There are only weak hydrophobic interactions in the interior of the membrane.

Which aspect of phospholipids is most important to the formation of bilayers?

They are amphipathic.

Refer to the figure. If you examine side A after three days, you should find _____.

a decrease in the concentration of NaCl and a decrease in the water level

Which of the following factors would tend to increase membrane fluidity?

a greater proportion of unsaturated phospholipids

Which of the following crosses lipid bilayers the fastest?

a small, nonpolar molecule like oxygen (O2)

Which of the following crosses lipid bilayers the slowest?

a sodium ion

Which of the following is a large organic molecule that is NOT assembled by polymerization of a few kinds of simple subunits?

a steroid

A membrane protein that spans the phospholipid bilayer one or more times is _____.

a transmembrane protein

For a protein to be an integral membrane protein, it would have to be _____.

amphipathic, with at least one hydrophobic region

Which of the following allows water to move much faster across cell membranes?

aquaporins

Lipids _____.

are insoluble in water

Steroids are considered to be lipids because they _____.

are not soluble in water

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

In some cells, there are many ion electrochemical gradients across the plasma membrane even though there are usually only one or two proton pumps present in the membrane. The gradients of the other ions are most likely accounted for by _____.

cotransport proteins

Based on the figure above, which of these experimental treatments would increase the rate of sucrose transport into the cell?

decreasing extracellular pH

Cooking oil and gasoline (a hydrocarbon) are not amphipathic molecules because they _____.

do not have a polar or charged region

The presence of cholesterol in the plasma membranes of some animal cells _____.

enables the membranes to stay fluid when cell temperature drops

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?

facilitated diffusion

Phospholipids and triglycerides both _____.

have a glycerol backbone

Which of the following increases the strength of the hydrophobic interactions in lipid bilayers and thus makes them less permeable to polar molecules?

increasing length of the hydrocarbon chains

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

Refer to the paragraph on Rhodopsins. Which of the following best describes this particular protein?

integral

Which term best describes the type of membrane protein in the figure?

integral

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

Celery stalks that are immersed in fresh water for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the fresh water_____.

is hypotonic and the salt solution is hypertonic to the cells of the celery stalks

The text states that ribonucleotides can diffuse through some types of liposomes. It is likely that the lipids present early in chemical evolution had short chains. Would liposomes formed from these types of lipids be more or less permeable to ribonucleotides than if early cells formed from long-chained lipids?

more permeable

Which of the following membrane activities requires energy from ATP?

movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid

A phospholipid is a _____.

nonpolar lipid molecule that is made amphipathic by the addition of a phosphate

Which of the following affects the osmolarity of a solution?

only II and III

Which of the following processes includes all others?

passive transport

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

phospholipids and proteins

Lipids that form membranes have what kind of structure?

polar heads and nonpolar tails; the polar heads interact with water

Refer to the figure. At the beginning of the experiment,

side A is hypotonic to side B.

Where would you most likely find an integral membrane protein?

spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell

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

What region of a steroid is hydrophilic?

the terminal hydroxyl group

Ions diffuse across membranes through specific ion channels down _____.

their electrochemical gradients