MICROSCOPES & MEMBRANES

You are monitoring the diffusion of a molecule across a membrane. Of the options listed below, the fastest rate of diffusion would result from an internal concentration of _______ μM and an external concentration of _______ μM. a) 5; 60 b) 35; 40 c) 50; 40 d) 50; 50 e) 100; 120

a) 5; 60

Suppose that a new drug shows promise in treating cancer because it can enter cells by simple diffusion. Which statement about the drug is false? a) It depends on a specific carrier protein to enter the cells. b) The drug molecules move from areas of higher concentration to areas of lower concentration. c) The rate of its diffusion is affected by temperature. d) Diffusion of the drug continues until its concentrations across membranes are in equilibrium. e) Diffusion of the drug molecules is a random process.

a) It depends on a specific carrier protein to enter the cells.

Which is a difference between a prokaryotic and a eukaryotic cell? a) The DNA in a prokaryotic cell is not enclosed in a membrane-bound nucleus. b) A prokaryotic cell does not use ribosomes for protein synthesis, whereas a eukaryotic cell does. c) Cellular processes in a prokaryotic cell are compartmentalized, whereas compartmentalization is absent in a eukaryotic cell. d) A prokaryotic cell is not enclosed by a cell membrane, and a eukaryotic cell is enclosed. e) A prokaryotic cell does not use DNA as its genetic material.

a) The DNA in a prokaryotic cell is not enclosed in a membrane-bound nucleus.

Which statement about a lipid bilayer is FALSE? a) The transmembrane space allows for the movement of charged particles. b) The outer layer contains hydrophilic portions of fatty acids. c) The transmembrane space allows for the diffusion of lipid-soluble particles. d) The transmembrane space contains hydrophobic regions of fatty acids. e) The outer layer contains polar groups that can interact with water.

a) The transmembrane space allows for the movement of charged particles.

How might a researcher study the presence of a specific protein in cells from different tissues of the body? a) Treat cells with a dye that selectively binds to the protein of interest, and look for evidence of this dye in cells, using light microscopy. b) Observe the protein in living cells, using light microscopy techniques that preserve cells in the living state. c) Slice cells into thin sections, use electron microscopy to take many images of structures inside the cells, and search for the protein in the images. d) Use scanning electron microscopy to search for the protein in the three-dimensional surfaces of whole cells. e) Use a general protein stain to treat cells before preparing them for bright-field microscopy, and then search for evidence of this dye in the samples.

a) Treat cells with a dye that selectively binds to the protein of interest, and look for evidence of this dye in cells, using light microscopy.

If a cell has an increased need for a particular molecule already present in a higher concentration within the cell than in the extracellular fluid, the cell might use active transport, which usually moves molecules a) in a direction opposite to the one in which diffusion moves them. b) from inside to outside the cell. c) toward higher pH. d) in the same direction as diffusion moves them. e) in a direction that tends to bring about equilibrium.

a) in a direction opposite to the one in which diffusion moves them.

Most plant and animal cells are a) large enough to be seen with a light microscope. b) smaller than a chloroplast. c) smaller than most bacteria. d) large enough to be seen with the unaided eye. e) larger than most fungal cells.

a) large enough to be seen with a light microscope.

Five statements about cell membranes are given. Which statement can be used to explain the importance of the cell membrane to cell survival? a) The cell membrane expands or shrinks by the addition or removal of phospholipid molecules. b) Cell membranes are selectively permeable with respect to molecules and ions. c) The cell membrane is so small that it is best viewed with an electron microscope. d) Cell membranes are composed of a phospholipid bilayer embedded with proteins. e) The cell membranes of prokaryotes and eukaryotes have the same basic structure.

b) Cell membranes are selectively permeable with respect to molecules and ions.

PICTURE: 3 red blood cells labeled A, B, and C. A is shriveled, B is normal, and C is bloated. Which statement regarding the red blood cells is true? a) Cell A has been immersed in a hypotonic solution. b) The concentration of solutes inside cell C is higher than in the solution surrounding the cell. c) Cell C has been immersed in a hypertonic solution. d) Osmosis occurs when a cell goes from condition B to C but not from condition B to A. e) Diffusion of solutes out of the cell is causing the events shown in the transition from condition B to A.

b) The concentration of solutes inside cell C is higher than in the solution surrounding the cell.

The hydrophilic regions of a membrane protein would most likely be found a) associated with the fatty acid region of the lipids. b) exposed on the surface of the membrane. c) only in cell membranes. d) in the interior of the membrane. e) either on the surface or inserted into the interior of the membrane.

b) exposed on the surface of the membrane.

The plasma membrane of the bacterium Pseudomonas syringae is able to remain fluid when it is extremely cold. The bacterium most likely accomplishes this by a) increasing the number of cholesterol molecules present. b) closing protein channels. c) replacing saturated fatty acids with unsaturated fatty acids. d) using fatty acids with longer tails. e) decreasing the number of hydrophobic proteins present.

c) replacing saturated fatty acids with unsaturated fatty acids.

One benefit of scanning electron microscopy is that it enables researchers a) to observe cells dividing. b) to sequence DNA molecules. c) to visualize 3-D topography of a cell or tissue sample. d) to determine the age of a cell. e) to follow metabolic reactions inside cells.

c) to visualize 3-D topography of a cell or tissue sample.

Which technique would be best suited to a study of normal cell migration during embryonic development? a) Electron microscopy b) Direct visual observation c) Experimentation on mutants d) Light microscopy e) Cell fractionation

d) Light microscopy

Two areas, A and B, are separated by a membrane that is permeable to a substance X. Which set of conditions will result in the greatest rate of diffusion of X into area A? a) The concentration of X in A is 200 mM; the concentration of X in B is 250 mM. b) The concentration of X in A is 5 mM; the concentration of X in B is 1 μM. c) The concentration of X in A is 50 mM; the concentration of X in B is 60 mM. d) The concentration of X in A is 10 mM; the concentration of X in B is 2 M. e) The concentration of X in A is 1 M; the concentration of X in B is 500 mM.

d) The concentration of X in A is 10 mM; the concentration of X in B is 2 M.

The speed and direction of ions as they move through channels in the cell membrane are determined by the a) number of channel proteins present. b) ability of the ions to bind water. c) size and charge of the ions. d) concentration gradient. e) thickness of the cell membrane.

d) concentration gradient.

Ribosomes are not visible under a light microscope, but they can be seen with an electron microscope because a) electron microscopes focus light with magnets. b) electrons have such high energy that they pass through biological samples. c) electron beams have more energy than light beams. d) electron microscopes have more resolving power than light microscopes. e) electron microscopes can be used to observe living cells.

d) electron microscopes have more resolving power than light microscopes.

A general function of all cellular membranes is to a) support the cell and determine its shape. b) produce proteins for the cell. c) move the cell. d) regulate which materials can enter or leave the cell. e) produce energy for the cell.

d) regulate which materials can enter or leave the cell.

A unicellular organism adapted to living in salt water is placed in a freshwater tank. What is the likely outcome? a) Water moves out of the cell, causing it to shrivel. b) Water and salt move in opposite directions until the organism can adapt. c) Water moves into the cell until the organism can adapt. d) Water moves out of the cell until the organism can adapt. e) Water moves into the cell, causing it to burst.

e) Water moves into the cell, causing it to burst.

In a biological membrane, the phospholipids are arranged with the fatty acid chains facing the interior of the membrane. As a result, the interior of the membrane is a) filled with water. b) hydrophilic. c) charged. d) polar. e) hydrophobic.

e) hydrophobic.