Chapter 7: Membrane Structure and Function

The internal solute concentration of a plant cell is about 0.8M. To demonstrate plasmolysis, it would be necessary to suspend the cell in what solution?

1.0M

How does cholesterol affect membrane fluidity?

At body temperature, it makes the membrane less fluid.

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

B; the diffusion gradient in cell B is steeper

Why is energy required for active transport?

Because it moves solutes against their concentration gradient.

If a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells?

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

What function do carbohydrates fulfill in the plasma membrane?

Cell-to-cell recognition

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?

Endocytosis

How does the "fluid mosaic model" describe the structure of the plasma membrane?

Proteins in the membrane contribute to the mosaic quality of the membrane while the lateral and rotational movements of phospholipids contribute to its fluidity.

Red blood cells contain approximately a 2% concentration of solutes. A red blood cell is placed into a solution that contains a 4% concentration of solutes to which the cell is not permeable. What will happen to the red blood cell?

The cell will decrease in size as water flows out of it.

Which of the following molecules is most likely to passively diffuse across the plasma membrane? a. Carbon dioxide b. Glucose c. Sodium ion d. DNA e. Hemoglobin

a. Carbon dioxide

Which of the following processes and organelle(s) accounts for the replacement of lipids and proteins lost from the plasma membrane? a. Exocytosis and smooth and rough ER b. Endocytosis and Golgi c. Active transport and the rough endoplasmic reticulum d. Receptor-mediated endocytosis and smooth ER and Golgi e. Flip-flop of phospholipids from one side of the plasma membrane to the other and the Golgi

a. Exocytosis and smooth and rough ER

Which of these statements describes some aspect of facilitated diffusion? a. Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane. b. Facilitated diffusion is another name for osmosis. c. Facilitated diffusion of solutes occurs through phospholipid pores in the membrane. d. Facilitated diffusion requires energy to drive a concentration gradient. e. There is only one kind of protein pore for facilitated diffusion.

a. Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane.

Which of the following molecules are most abundant in the plasma membrane? a. Phospholipids b. Proteins c. Carbohydrates d. Cholesterol e. Water

a. Phospholipids

Which of the following cell structures exhibits selective permeability between a cell and its external environment? a. Plasma membrane b. Mitochondria c. Chloroplasts d. Endoplasmic e. Lysosomes

a. Plasma membrane

Which of the statements is not true? a. Osmosis is a completely passive process. b. Bacterial cells burst if placed in a hypotonic solution. c. Isotonic solutions have equal solute concentrations. d. Osmosis is the diffusion of water across membranes. e. All of the above choices are accurate statements.

b. Bacterial cells burst if placed in a hypotonic solution.

Which of the following molecules will diffuse most quickly across a lipid bilayer membrane? a. H2O b. O2 c. H2PO4- d. Glucose e. Na+

b. O2

In facilitated diffusion, __________ proteins provide openings in the plasma membrane for substances to flow through without changing structure, and __________ proteins allow passage of substances through the plasma membrane after undergoing a subtle change in shape.

channel; carrier

Which of the following is not a good explanation for why the plasma membrane assembles the way it does? a. Water predominates both outside and inside cells. b. The hydrophobic nature of the interior of the membrane allows it to have fluidity. c. The hydrophobic ends of the phospholipids cannot interact with an aqueous environment. d. The amphipathic nature of the phospholipids allows the membrane to be mono-layered. e. None of the above choices are correct.

d. The amphipathic nature of the phospholipids allows the membrane to be mono-layered.

Which of the following amino acids would most likely be present in the transmembrane domain of an integral membrane protein? a. a charged amino acid like lysine b. a polar amino acid like serine c. a special amino acid like glycine or proline d. a hydrophobic amino acid like valine e. any of the above, with no preference

d. a hydrophobic amino acid like valine

The plasma membrane exhibits selective permeability. This means that __________.

the plasma membrane allows some substances to flow through it more easily than others

The sodium-potassium pump __________.

transports sodium ions out of the cell and transports potassium ions into the cell

Which of the following plant cells would exhibit the most turgor pressure? a. A cell placed in a hypotonic solution b. A cell placed in an isotonic solution c. A cell placed in a hypertonic solution d. None of the listed responses is correct. e. All of the listed responses are correct.

a. A cell placed in a hypotonic solution

Which of the following would be least likely to diffuse through a plasma membrane without the help of a transport protein? a. A large polar molecule b. A large nonpolar molecule c. Dissolved gases such as oxygen or carbon dioxide d. A small nonpolar molecule e. Any of the above would easily diffuse through the membrane.

a. A large polar molecule

Which of the following substances would be most likely to pass through the plasma membrane without the help of a transport protein? a. A nonpolar molecule, such as a hydrocarbon b. A large polar molecule c. A negatively charged ion d. Water e. Glucose

a. A nonpolar molecule, such as a hydrocarbon

Which of the following is a correct difference between active transport and facilitated diffusion? a. Active transport requires energy from ATP, and facilitated diffusion does not. b. Active transport involves transport proteins, and facilitated diffusion does not. c. Facilitated diffusion can move solutes against a concentration gradient, and active transport cannot. d. Active transport can move solutes in either direction across a membrane, but facilitated diffusion can only move in one direction. e. Facilitated diffusion involves transport proteins, and active transport does not.

a. Active transport requires energy from ATP, and facilitated diffusion does not.

Which of the following statements about diffusion is true? a. It is a passive process. b. It is very rapid over long distances. c. It requires expenditure of energy by the cell. d. It occurs when molecules move from a region of lower concentration to a region of higher concentration. e. It always requires integral proteins of the cell membrane.

a. It is a passive process.

Which of the following statements concerning carbohydrates associated with the plasma membrane is correct? a. Membrane carbohydrates function primarily in cell-cell recognition. b. Carbohydrates are only found associated with the membranes of prokaryotic cells. c. The carbohydrate composition of most eukaryotic plasma membranes is quite similar. d. Carbohydrates on the plasma membrane are typically short chains of between two and five monosaccharides. e. Carbohydrates associated with the plasma membrane are located on both surfaces of the membrane.

a. Membrane carbohydrates function primarily in cell-cell recognition.

Which of the following statements about passive transport is correct? a. Passive transport permits the solute to move in either direction, but the net movement of the population of solute molecules occurs down the concentration gradient of the molecule. b. Passive transport operates independently of diffusion. c. Passive transport operates independently of the concentrations of the moving solute. d. In passive transport, solute movement stops when the solute concentration is the same on both sides of the membrane. e. Passive transport does not occur in the human body.

a. Passive transport permits the solute to move in either direction, but the net movement of the population of solute molecules occurs down the concentration gradient of the molecule.

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

a. Phospholipids form a selectively permeable structure.

Which of the following structural arrangements of the components in biological membranes facilitates the cell membrane's property of selective permeability? a. Proteins embedded in two layers of phospholipids b. Proteins sandwiched between two layers of phospholipids c. A layer of protein coating a layer of phospholipid d. Phospholipids sandwiched between two layers of protein e. A phospholipid bilayer with proteins scattered on the surfaces of the membranes

a. Proteins embedded in two layers of phospholipids

Which of the following is not a property of both exocytosis and endocytosis? a. Specific molecules can be bound by receptors and contained within a vesicle. b. The membrane of the vesicle is at some point part of the plasma membrane of the cell. c. Large molecules can be transported from one location to another. d. All of the above choices are correct. e. None of the above choices are correct.

a. Specific molecules can be bound by receptors and contained within a vesicle.

A cell is placed into a solution and the cell shrinks. Which of the following is true regarding the solution? a. The solution is hypertonic. b. The solution has the same solute concentration as the cell. c. The solution is hypotonic. d. The cell is hypertonic. e. None of the listed responses is correct.

a. The solution is hypertonic.

Which of the following is correct regarding peripheral proteins? a. These proteins are found only on the surface of the plasma membrane. b. They span the entire phospholipid bilayer. c. They exhibit only hydrophobic properties. d. They have no specific function in the plasma membrane. e. These proteins exhibit both hydrophilic and hydrophobic properties.

a. These proteins are found only on the surface of the plasma membrane.

Which of the following is correct regarding integral proteins? a. These proteins exhibit both hydrophilic and hydrophobic properties. b. These proteins are found only on the surface of the plasma membrane. c. They exhibit only hydrophilic properties. d. They exhibit only hydrophobic properties. e. They have no specific function in the plasma membrane.

a. These proteins exhibit both hydrophilic and hydrophobic properties.

Which of the following statements about osmosis is correct? a. If a cell is placed in an isotonic solution, more water will enter the cell than leaves the cell. b. The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis. c. If a solution outside the cell is hypertonic compared to the cytoplasm, water will move into the cell by osmosis. d. Osmosis is the diffusion of water from a region of lower water concentration to a region of higher water concentration. e.All ofthe above choices are correct.

b. The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis.

An oligosaccharide (a short stretch of monosaccharides) covalently linked to a lipid in the lumen of the rough ER may end up on the ________________.

b. extracellular face of the plasma membrane.

Phagocytosis, pinocytosis, and receptor-mediated endocytosis all involve ____________.

b. invagination of the plasma membrane.

Which of the following forms of cell interaction would be conducted through gap junctions? a. Anchoring of cells together and to the cytoplasm. b. Restricting movement of dissolved materials between cells. c. Allowing molecules to pass through channels between cells. d. All of the above choices are correct. e. None of the above choices are correct.

c. Allowing molecules to pass through channels between cells.

If a marine algal cell is suddenly transferred from seawater to freshwater, the algal cell will initially ____________.

c. absorb water and increase in volume.

All cells have voltages across their membranes. This voltage is called a(n) __________ and is often maintained by __________.

membrane potential; electrogenic pumps