chapter 7 membrane function and structure

Which of the following statements about diffusion is true?

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

The membranes of winter wheat are able to remain fluid when it is extremely cold by ________.

) increasing the proportion of unsaturated phospholipids in the membrane

In which of the following environments would there be the greatest need for osmoregulation

A salmon moving from a river into an ocean

Which of the following statements 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

Which of the following statements correctly describes osmosis?

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

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

O2

Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this fact most probably mean?

Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life

What will happen to a red blood cell (RBC), which has an internal ion content of about 0.9%, if it is placed into a beaker of pure water

The cell would swell because the water in the beaker is hypotonic relative to the cytoplasm of the RBC.

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

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

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.

Cell membranes have distinct inside and outside faces. Which of the following statements is the most likely explanation for the membrane's asymmetrical nature?

The two sides of a cell membrane face different environments and carry out different functions.

The force driving simple diffusion is ________, while the energy source for active transport is ________.

a concentration gradient, ATP hydrolysis

Which of the following structures would decrease the electrochemical gradient across a membrane?

a potassium channel

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 statements correctly describes the normal tonicity conditions for typical plant and animal cells? The animal cell is in ________.

an isotonic solution, and the plant cell is in a hypotonic solution

Which of the following molecules dramatically increases the rate of diffusion of water across cell membranes?

aquaporins

According to the fluid mosaic model of cell membranes, phospholipids ________.

can move laterally along the plane of the membrane

An animal cell lacking carbohydrates on the external surface of its plasma membrane would likely be impaired in which function?

cell-cell recognition

In what way do the membranes of a eukaryotic cell vary

certain proteins are unique to each membrane

Which of the following types of molecules lack hydrophilic domains?

cholesterol

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. In this bacterial 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

Familial hypercholesterolemia is characterized by ________.

defective LDL receptors on the cell membranes

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 not fatal because we have developed which of the following types of treatments?

hydrating drinks with high concentrations of salt and glucose

Diffusion of ions across membranes through specific ion channels is driven by ________.

ion electrochemical gradients

According to the fluid mosaic model, a membrane ________.

is composed of a fluid bilayer of phospholipids with embedded amphipathic 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 sodium-potassium pump is called an electrogenic pump because it ________.

is used to drive the transport of glucose against a concentration gradient

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

it exhibits specificity for a particular type of molecule

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

lysosomes

The voltage across a membrane is called the ________.

membrane potential

Which of the following membrane activities requires energy from ATP hydrolysis?

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

A sodium-potassium pump ________.

moves three sodium ions out of a cell and two potassium ions into a cell using energy from ATP hydrolysis

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

on the inside surface of the vesticle

Which of the following processes includes all of the others

passive transport

Which of the following types of molecules are hydrophilic and therefore excluded from the hydrophobic portion of the phospholipid bilayer?

peripheral membrane proteins

A phospholipid bilayer with equal amounts of saturated and unsaturated fatty acids displays a specific permeability to glucose. What effect will increasing the proportion of unsaturated fatty acids in the bilayer have on the membrane's permeability to glucose?

permeability to glucose will increase

An organism with a cell wall would most likely be unable to take in materials through ________.

phagocytosis

White blood cells engulf bacteria using ________.

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

When a plant cell, such as one from a tulip leaf, is submerged in a hypertonic solution, what is likely to occur?

plasmolysis will shrink the interior of the cell

A research team is working on the design of a new drug for the treatment of lung cancer. To be most effective, this drug must specifically enter the cytoplasm of lung cells while not entering the cells of other tissues. Which of the following characteristics would likely enhance the specificity of this drug?

similarity of the drug molecule to other molecules normally transported lung cells

What kinds of molecules pass through a cell membrane most easily

small and hydrophobic

Which of the following are least likely to diffuse through the phospholipid bilayer of a cell membrane?

small ions

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

there are only weak hydrophobic interactions in the interior of the membrane

When a cell is in equilibrium with its environment, which of the following processes occurs for substances that can diffuse through the plasma membrane?

there is random movement of substances into and out of the cell