Chapter 7

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 _______.

1) B 2) The diffusion gradient in cell B is steeper

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?

1.0 M

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?

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

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?

A hypertonic sucrose solution

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

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.

Which statements about the sidedness of the plasma membrane is correct?

All of the listed responses are correct.

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?

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

Which of the following statements about cotransport of solutes across a membrane is correct?

Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes.

Which of the following correctly describes a general property of all electrogenic pumps?

Eletrogenic pumps create a voltage difference across the membrane.

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 not a function of membrane proteins?

Energy, carbon, and nitrogen storage

Which of the following processes and organelles account for the replacement of lipids and proteins lost from the plasma membrane?

Exocytosis and smoother ER and rough ER

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. Which of the following best describes a mechanism by which Ca2+ enters the cell?

Facilitated diffusion of Ca2+ into the cell down its electrochemical gradient

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 the following is false in regard to facilitated diffusion?

Facilitated diffusion requires the hydrolysis of ATP

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

In the interior of the membrane

Which of the following statements about diffusion is true?

It is a passive process.

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

Membrane carbohydrates function primarily in cell-cell recognition

Which of the following functions of membrane proteins is important in tissue formation during embryonic development in animals?

Membrane proteins with short sugar chains form identification tags that are recognized by other cells.

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?

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

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

On the outside (external) surface of the membrane.

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 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?

Phospholipids form a selectively permeable structure.

Which of the following pairs correctly matches a membrane transport process to its primary function?

Pinocytosis: the uptake of water and small solutes into the cell by formation of vesicles at the plasma membrane

Which of the following enables a cell to pick up and concentrate a specific kind of molecule?

Receptor-mediated endocytosis

The plasma membrane is referred to as a "fluid mosaic" structure. Which of the following statements about that model is true?

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?

The movement of protons through the cotransport protein cannot occur unless sucrose moves at the same time.

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

The plasma membrane

Active transport requires an input of energy and can also generate voltages across membranes. Based on this information, which of the following statements is true?

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

Which of the following statements about the sodium-potassium pump is correct?

The sodium-potassium pump moves Na+ out and two K+ in for a net transport of one positive charge out of the cell.

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. Which of the following statements about this mechanism is accurate?

To pump glucose up its concentration gradient, sodium moves down its concentration gradient, and the distribution of sodium ions across the membrane forms an electrochemical gradient that drives this mechanism.

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?

Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease.