Chapter 7

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

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

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

the plasma membrane

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

Why is energy required for active transport?

Because it moves solutes against their concentration gradient

Which of the following statements about passive transport is correct?

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 molecules are most abundant in the plasma membrane? Carbohydrates Cholesterol Phospholipids Water Proteins

Phospholipids

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

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

Which of the following is correct regarding integral proteins?

These proteins exhibit both hydrophilic and hydrophobic properties.

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

carbon dioxide

Which of the following statements about diffusion is true?

it is a passive process

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

A cell placed in a hypotonic solution In a hypotonic solution, the plant cell would take up water. The cells of plants, prokaryotes, fungi, and some protists are surrounded by cell walls. When such a cell is immersed in a hypotonic solution—bathed in rainwater, for example—the cell wall helps maintain the cell's water balance. Consider a plant cell. Like an animal cell, the plant cell swells as water enters by osmosis. However, the relatively inelastic cell wall will expand only so much before it exerts a back pressure on the cell, called turgor pressure, that opposes further water uptake. At this point, the cell is turgid (very firm), which is the healthy state for most plant cells.

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

A large polar molecule 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? A negatively charged ion Water Glucose A large polar molecule A nonpolar molecule, such as a hydrocarbon

A nonpolar molecule, such as a hydrocarbon

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

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

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

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

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.

Which of these statements describes some aspect of facilitated diffusion?

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

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

Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane. Facilitated diffusion is a type of passive diffusion in which polar molecules and some ions use transport proteins to cross the membrane. These proteins are either channel proteins or carrier proteins. Channel proteins provide channels for molecules or ions to cross, whereas carrier proteins move substances across the membrane by changing their shapes. Facilitated diffusion does not occur through phospholipid pores, but through integral membrane transport proteins. It does not require cellular energy, but is driven solely by the concentration gradient inside vs outside the cell.

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

Membrane carbohydrates function primarily in cell-cell recognition

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.

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?

Proteins embedded in two layers of phospholipids

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.

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

membrane potential; electrogenic pumps