Chapter 7 Practice Questions

The internal solute concentration of a plant cell is about 0.8 M. To demonstrate plasmolysis, it would be necessary to suspend the cell in what solution? (Concept 7.3) 0.8 M 0.4 M 150 mM. distilled water 1.0 M

1.0M (the solution is hypertonic, which will make water leave the cell) distilled water = turgid 0.8 = flaccid

Green olives may be preserved in brine, which is a 30% salt solution. How does this method of preservation prevent microorganisms from growing in the olives? (Concept 7.3)

A 30% salt solution is hypertonic to the bacteria, so they lose too much water and undergo plasmolysis.

Cells A and B are the same size, shape, and temperature, but cell A is metabolically less active than cell B. and cell B is actively converting oxygen to water in cellular respiration. Oxygen will diffuse more rapidly into cell __________ because __________. (Concept 7.3)

B; the diffusion gradient in cell B is steeper

Seawater is hypertonic to cytoplasm in vertebrate cells and in plant cells. If a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells? (Concept 7.3)

Both cells would lose water; the red blood cell would shrivel, and the plant's plasma membrane would pull away from the cell wall

T/F: Facilitated diffusion requires the hydrolysis of ATP.

False Needs only the concentration gradient - no energy is required

T/F: The carbohydrate composition of most eukaryotic plasma membranes is quite similar.

False (Variation in carbohydrate composition of the plasma membrane is critical in cellular recognition)

T/F: Carbohydrates associated with the plasma membrane are located on both surfaces of the membrane.

False (the primary location of carbohydrates is on the outer surface of the plasma membrane)

T/F: In passive transport, solute movement stops when the solute concentration is the same on both sides of the membrane.

False (when the concentration is the same on both sides of the membrane, passive transport continues, but the rate of transport is the same in both directions)

T/F: Cotransport involves the hydrolysis of ATP by the transporting protein.

False Cotransport proteins use the energy of gradients created by the ATP-dependent pumps

Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the plasma membrane would cholesterol most likely be found? (Concept 7.1)

In the interior of the membrane

A selectively permeable membrane separates two solutions. Water is able to pass through this membrane; however, sucrose (a disaccharide) and glucose (a monosaccharide) cannot pass. The membrane separates a 0.2-molar sucrose solution from a 0.2-molar glucose solution. With time, how will the solutions change? (Concept 7.3)

Nothing will happen, because the two solutions are isotonic to one another

The plasma membrane is referred to as a "fluid mosaic" structure. What does this mean? (Concept 7.1)

The fluid aspect of the membrane is due to the lateral and rotational movement of phospholipids, and embedded proteins account for the mosaic aspect.

Consider the transport of protons and sucrose into a plant cell by the sucrose-proton cotransport protein. Plant cells continuously produce a proton gradient by using the energy of ATP hydrolysis to pump protons out of the cell. Why, in the absence of sucrose, do protons not move back into the cell through the sucrose-proton cotransport protein? (Concept 7.4)

The movement of protons through the cotransport protein cannot occur unless sucrose moves at the same time. (coupling needs to occur)

How does the sodium-potassium pump generate voltage across the cell membrane?

The sodium-potassium pump hydrolyzes ATP and results in a net positive change outside the cell membrane.

T/F: Diffusion is synonyms with being a passive process.

True

T/F An electrogenic pump creates a net charge difference across a membrane.

True This is called a membrane potential

A single plant cell is placed in an isotonic solution. Salt is then added to the solution. Which of the following would occur as a result of the salt addition? (Concept 7.3)

Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease (plasmolyze)

The concentration of solutes in a red blood cell is about 2%, but red blood cells contain almost no sucrose or urea. Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions? (Concept 7.3)

a hypertonic sucrose solution (cannot be urea because it is permeable and will simply diffuse through the membrane)

What kind of molecule would be LEAST likely to diffuse through a plasma membrane without the help of a transport protein? (Concept 7.2)

a large, polar molecule

The ________ distribution of membrane proteins, lipids, and carbohydrates across the plasma membrane is determined as the membrane is being ________.

asymmetrical; constructed

The sucrose co-transport protein is: a. Very non specific in that it can bind to a very large number of different solutes b. Usually associated with a proton pump c. Usually associated with a Na+/K+ pump d. Insensitive to temperature e. Directly reacted with ATP

b. Usually associated with a proton pump

Receptor-mediated endocytosis differs from phagocytosis in that... a. phagocytosis is very specific for what is taken into the cell. b. receptor-mediated endocytosis is very specific for what is taken into the cell. c. fusion of vesicles with lysosomes takes place only in phagocytosis. d. fusion of vesicles with lysosomes takes place only in receptor-mediated endocytosis. e. coated vesicles are formed in phagocytosis.

b. receptor-mediated endocytosis is very specific for what is taken into the cell.

Facilitated diffusion and active transport both: a. require ATP. b. require protein carriers. c. can move molecules down their concentration gradient. d. show higher rates without limit as solute concentration increases. e. depend on the solubility of the solute in lipid.

b. require protein carriers.

Which of the following factors tends to increase membrane fluidity? a. A lower temperature b. A relatively high protein content in the membrane c. A greater proportion of unsaturated phospholipids d. A greater proportion of relatively large glycolipids compared to lipids having smaller molecular weights e. A high membrane potential

c. A greater proportion of unsaturated phospholipids (higher temperature * more cholesterol)

Which of the following functions of membrane proteins is important in tissue formation during embryonic development in animals? (Concept 7.1) a. Membrane proteins possess enzymatic activity. b. Membrane proteins form channels, which move substances across the membrane. c. Membrane proteins with short sugar chains form identification tags that are recognized by other cells. d. Membrane proteins attach the membrane to the cytoskeleton. e. All of the listed responses are correct.

c. Membrane proteins with short sugar chains form identification tags that are recognized by other cells. (cell-cell recognition is important in tissue formation during embryogenesis)

Which of the following statements about the role of phospholipids in the structure and function of biological membranes is correct? (Concept 7.1) a. Phospholipids are completely unable to interact with water. b. They are triacylglycerols, which are commonly available in foods. c. Phospholipids form a selectively permeable structure. d. Phospholipids form a structure in which the hydrophobic portion faces outward. e. Phospholipids form a single sheet in water.

c. Phospholipids form a selectively permeable structure.

Facilitated diffusion and simple diffusion both: a. require ATP. b. require protein carriers. c. can move molecules down their concentration gradient. d. show higher rates without limit as solute concentration increases. e. depend on the solubility of the solute in lipid.

c. can move molecules down their concentration gradient.

Which of the following molecules is most likely to passively diffuse across the plasma membrane? (Concept 7.2) DNA sodium ion carbon dioxide hemoglobin glucose

carbon dioxide

Facilitated diffusion may occur through what 2 proteins in the membrane?

channel or transport

Parts of proteins that are exposed on the cytoplasmic side of the ER are also exposed on the ...

cytoplasmic side of the plasma membrane

The passive movement of a solute down its concentration gradient is termed:

diffusion (simple)

Osmotic pressure is produced by the concentration of ________ substances and is not influenced by the relative sizes of the ________.

dissolved; solute

Which of the following is NOT a function of membrane proteins? (Concept 7.1) a. enzymatic activity b. cell-cell recognition c. transport d. intercellular joining e. energy, carbon, and nitrogen storage

e. energy, carbon, and nitrogen storage

Passive transport permits the solute to move in ______ direction, but the net movement of solute molecules occurs _________ of the molecule.

either; down the concentration gradient

Glucose can be moved into cells via an active transport mechanism when the concentration of glucose inside the cell is higher than the concentration of glucose outside of the cell. This active transport mechanism moves glucose and sodium into the cell at the same time. The glucose moves up its gradient and the sodium moves down its gradient. What kind of gradient is this?

electrochemical gradient that drives this mechanism example of coupling

A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mother's milk. These molecules probably enter the cells lining the baby's digestive tract via which process? (Concept 7.5)

endocytosis (procedure that cells use to import large molecules across their plasma membrane)

What are the three organelles that account for the replacement of lipids and proteins lost from the plasma membrane? (Concept 7.5)

exocytosis, sER, and rER exocytosis - derived from the endomembrane and increases the # of phospholipids sER - responsible for the production of lipids destined rER - produces proteins destined for the plasma membrane

A cell has a membrane potential of -100 mV (more negative inside than outside) and has 1,000 times more calcium ions outside the cell than inside. What best describes a mechanism by which Ca2+ enters the cell? (Concept 7.4)

facilitated diffusion of Ca2+ into the cell down its electrochemical (electrical + chemical) gradient (as long as there is a channel or carrier protein that is specific for Ca2+)

The sodium-potassium pump establishes concentration gradients of...

higher potassium (K) concentrations inside the cell and higher sodium (Na) concentrations outside the cell 3 Na+ leave and 2 K+ come inside --> electrogenic pump

Facilitated diffusion requires ______ proteins, but passive diffusion does not.

integral

Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the membrane would carbohydrates most likely be found? (Concept 7.1)

on the outside (external) surface of the membrane

Every integral protein has a specific _________ in the plasma membrane

orientation

A cell takes in dissolved materials by forming tiny vesicles around fluid droplets trapped by folds of the plasma membrane. This process is:

pinocytosis

Which of the following enables a cell to pick up and concentrate a specific kind of molecule? (Concept 7.5) facilitated diffusion passive transport osmosis receptor-mediated endocytosis channel proteins

receptor-mediated endocytosis (only a specific molecule called a ligand can bind to the receptor)

Biological membranes are normally directly permeable to ________________ molecules, which can undergo simple diffusion across the membrane.

simple & hydrophobic

The electrochemical gradient created by a single ATP-dependent pump can drive the transport of many different ________ using ____________ proteins.

solutes; cotransport

The two lipid layers may differ in ...

specific lipid composition

The number and types of proteins differ between the inner and the outer surfaces of membranes. The reason for this is:

the functions of the membrane differ on each side