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

Which of the following plant cells would exhibit the most turgor pressure?

Answer: A cell placed in a hypotonic solution -A cell placed in a hypotonic solution - A cell placed in an isotonic solution -A cell placed in a hypertonic solution -None of the listed responses is correct. -All of the listed responses are correct.

How does cholesterol affect membrane fluidity?

At body temperature, it makes the membrane less fluid.

Why is energy required for active transport?

Because it moves solutes against their concentration gradient To pump a solute across a membrane against its gradient requires work; the cell must expend energy. Therefore, this type of membrane traffic is called active transport. The transport proteins that move solutes against their concentration gradients are all carrier proteins rather than channel proteins.

What function do carbohydrates fulfill in the plasma membrane?

Cell-to-cell recognition

Which of the following processes and organelle(s) accounts for the replacement of lipids and proteins lost from the plasma membrane?

Exocytosis and smooth and rough ER Exocytosis and the smooth and rough ER play important roles in replacing lipids and proteins in the cell membrane. Exocytosis is the process whereby transport vesicles move to the cell membrane and fuse with it as they release their contents into the extracellular space, leading to the replacement of cell membrane phospholipids. The smooth ER produces lipids destined for the membrane, whereas the rough ER produces proteins destined for the plasma membrane.

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. Since the concentration of solutes in the solution is higher than that in the cell, the cell is in a hypertonic environment. Cells lose water in this type of environment.

A cell is placed into a solution and the cell shrinks. Which of the following is true regarding the solution?

The solution is hypertonic.

Which of the following molecules are most abundant in the plasma membrane?

Answer: Phospholipids - Phospholipids -Proteins -Carbohydrates -Cholesterol -Water

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

Which of the following would be least likely to diffuse through a plasma membrane without the help of a transport protein?

Answer: A large polar molecule - A large polar molecule -A large nonpolar molecule -Dissolved gases such as oxygen or carbon dioxide -A small nonpolar molecule -Any of the above would easily diffuse through the membrane. A large polar molecule would be the least likely to passively diffuse through a plasma membrane without the help of a transport protein. Both its size and the hydrophobic interior of the membrane would restrict it.

Which of the following substances would be most likely to pass through the plasma membrane without the help of a transport protein?

Answer: A nonpolar molecule, such as a hydrocarbon -A nonpolar molecule, such as a hydrocarbon -A large polar molecule -A negatively charged ion -Water -Glucose

Which of the following is a correct difference between active transport and facilitated diffusion?

Answer: Active transport requires energy from ATP, and facilitated diffusion does not. - Active transport requires energy from ATP, and facilitated diffusion does not. -Active transport involves transport proteins, and facilitated diffusion does not. -Facilitated diffusion can move solutes against a concentration gradient, and active transport cannot. -Active transport can move solutes in either direction across a membrane, but facilitated diffusion can only move in one direction. - Facilitated diffusion involves transport proteins, and active transport does not.

Which of these statements describes some aspect of facilitated diffusion?

Answer: Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane. - Facilitated diffusion is another name for osmosis. -Facilitated diffusion of solutes occurs through phospholipid pores in the membrane. -Facilitated diffusion requires energy to drive a concentration gradient. -There is only one kind of protein pore for facilitated diffusion.

Which of the following statements about diffusion is true?

Answer: It is a passive process -It is a passive process. -It is very rapid over long distances. It requires expenditure of energy by the cell. -It occurs when molecules move from a region of lower concentration to a region of higher concentration. -It always requires integral proteins of the cell membrane. Diffusion occurs slowly over long distances. It is a passive process that does not require the expenditure of energy by the cell. The molecules of a substance diffuse from an area of higher concentration to an area of lower concentration, spreading out to fill the available space. Passive diffusion does not depend on the presence of integral proteins; however, facilitated diffusion, which is also a passive process, does.

Which of the following statements concerning carbohydrates associated with the plasma membrane is correct?

Answer: Membrane carbohydrates function primarily in cell-cell recognition. -Membrane carbohydrates function primarily in cell-cell recognition. -Carbohydrates are only found associated with the membranes of prokaryotic cells. -The carbohydrate composition of most eukaryotic plasma membranes is quite similar. -Carbohydrates on the plasma membrane are typically short chains of between two and five monosaccharides. -Carbohydrates associated with the plasma membrane are located on both surfaces of the membrane.

Which of the following statements about passive transport is correct?

Answer: 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. - 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. -Passive transport operates independently of diffusion. -Passive transport operates independently of the concentrations of the moving solute. -In passive transport, solute movement stops when the solute concentration is the same on both sides of the membrane. -Passive transport does not occur in the human body.

Which of the following statements about the role of phospholipids in the structure and function of biological membranes is correct?

Answer: Phospholipids form a selectively permeable structure. - Phospholipids are completely insoluble in water. -Phospholipids form a single sheet in water. -Phospholipids form a structure in which the hydrophobic portion faces outward. -They are triacylglycerols, which are commonly available in foods.

Which of the following structural arrangements of the components in biological membranes facilitates the cell membrane's property of selective permeability?

Answer: Proteins embedded in two layers of phospholipids - Proteins embedded in two layers of phospholipids -Proteins sandwiched between two layers of phospholipids -A layer of protein coating a layer of phospholipid -Phospholipids sandwiched between two layers of protein -A phospholipid bilayer with proteins scattered on the surfaces of the membranes

Which of the following is correct regarding peripheral proteins?

Answer: These proteins are found only on the surface of the plasma membrane. -These proteins are found only on the surface of the plasma membrane. -They span the entire phospholipid bilayer. -They exhibit only hydrophobic properties. -They have no specific function in the plasma membrane. -These proteins exhibit both hydrophilic and hydrophobic properties.

Which of the following is correct regarding integral proteins?

Answer: These proteins exhibit both hydrophilic and hydrophobic properties. - These proteins exhibit both hydrophilic and hydrophobic properties. -These proteins are found only on the surface of the plasma membrane. -They exhibit only hydrophilic properties. -They exhibit only hydrophobic properties. - They have no specific function in the plasma membrane

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.

Which of the following molecules is most likely to passively diffuse across the plasma membrane?

Carbon dioxide Nonpolar molecules like carbon dioxide, hydrocarbons, and oxygen are hydrophobic and dissolve in the lipid bilayer, crossing the cell membrane easily through passive diffusion. Ions and polar molecules, however, are hydrophilic and cannot cross the hydrophobic interior of the membrane without a carrier.

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 The key terms here are "large protein molecules." Both passive and active transport move small molecules across cell membranes. Osmosis refers to the movement of free water, not antibodies, across a membrane. Exocytosis removes large molecules from cells. Endocytosis is the process used by cells to import large molecules, such as antibodies, across the plasma membrane.

Which of the following cell structures exhibits selective permeability between a cell and its external environment?

Plasma membrane

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

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

membrane potential; electrogenic pumps

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