MasteringBio: Membranes and Membrane Transport Part 2

Which line or lines represent(s) bags that contain a solution that is hypertonic at the end of 60 minutes?

B

After the system reaches equilibrium, what changes are observed?

The water level is higher in side A than in side B.

Because ions carry a charge (positive or negative), their transport across a membrane is governed not only by concentration gradients across the membrane but also by differences in charge across the membrane (also referred to as membrane potential). Together, the concentration (chemical) gradient and the charge difference (electrical gradient) across the plasma membrane make up the electrochemical gradient. Consider the plasma membrane of an animal cell that contains a sodium-potassium pump as well as two non-gated (always open) ion channels: a Na+ channel and a K+ channel. The effect of the sodium-potassium pump on the concentrations of Na+ and K+ as well as the distribution of charge across the plasma membrane is indicated in the figure bhttp://session.masteringbiology.com/problemAsset/1119630/24/1119630_010.jpgelow. Which of the following statements correctly describe(s) the driving forces for diffusion of Na+ and K+ ions through their respective channels? Select all that apply. 1. The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane. 2. The diffusion of Na+ ions into the cell is impeded by the electrical gradient across the plasma membrane. 3. The diffusion of K+ ions out of the cell is impeded by the K+ concentration gradient across the plasma membrane. 4. The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane. 5.The electrochemical gradient is larger for Na+ than for K+.

1. The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane. 4. The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane. 5.The electrochemical gradient is larger for Na+ than for K+. -The concentration gradient of Na+ ions across the membrane (higher Na+ concentration outside) facilitates the diffusion of Na+ into the cell. At the same time, the electrical gradient across the membrane (excess positive charge outside) drives Na+ into the cell. The concentration gradient of K+ ions across the membrane (higher K+ concentration inside) facilitates the diffusion of K+ out of the cell. However, the electrical gradient across the membrane (excess positive charge outside) impedes the diffusion of K+ out of the cell. The electrochemical gradient for an ion is the sum of the concentration (chemical) gradient and the electrical gradient (charge difference) across the membrane. For Na+ ions, diffusion through the Na+ channel is driven by both the concentration gradient and the electrical gradient. But for K+ ions, the electrical gradient opposes the concentration gradient. Therefore, the electrochemical gradient for Na+ is greater than the electrochemical gradient for K+.

Which line represents the bag with the highest initial concentration of sucrose?

A

All cells contain ion pumps that use the energy of ATP hydrolysis to pump ions across the plasma membrane. These pumps create an electrochemical gradient across the plasma membrane that is used to power other processes at the plasma membrane, including some transport processes. In animal cells, the main ion pump is the sodium-potassium pump. -OUTSIDE CELL B. ([Na+]low, [K+]high) or ([Na+]high,[K+]low) C. (excess + charge) or (excess - charge) -(BETWEEN) A. (3[Na+]v,2[K+]^)，（2[Na+]^,3[K+]v), (3[Na+]^,2[K+]v) -INSIDE CELL D. ([Na+]low,[K+]high) or ([Na+]high,[K+]low) E. (excess + charge) or (excess - charge)

B.[Na+]high [K+]low C. excess + charge A. 3 Na+ ^ 2 K+ v D. [Na+]low [K+]high E. excess - charge -Active transport by the sodium-potassium pump follows this cycle. 1. Three Na+ ions from the cytosol bind to the pump. 2. The binding of Na+ stimulates the phosphorylation of the pump protein by ATP. 3. Phosphorylation causes a conformational change in the pump that moves the three Na+ ions against their concentration gradient and releases them outside the cell. 4. The release of the Na+ ions permits two K+ ions from outside the cell to bind to the pump, and the phosphate group is released. 5. Release of the phosphate group causes another conformational change in the pump. 6. The conformational change in the pump moves the two K+ ions against their concentration gradient and releases them into the cytosol. http://session.masteringbiology.com/problemAsset/1119630/24/1119630_009.jpg The net result is that the concentration of Na+ is higher outside the cell and the concentration of K+ is higher inside the cell. In addition, one more positive charge has been transported out of the cell than into the cell, leaving the outside of the cell with an excess positive charge and the inside with an excess negative charge. Thus, the sodium-potassium pump creates both chemical gradients and charge differences across the plasma membrane. The function of the sodium-potassium pump in animal cells (and the proton pump in bacteria and plant cells) is essential to many cell functions. It prevents chemical and electrical gradients across the plasma membrane from reaching equilibrium (at which point the cell would be dead) and powers many types of active transport across the plasma membrane.

Which of the following statements is TRUE with regard to this animation?

Both sodium and potassium ions are transported against their concentration gradients. (Correct. Both ions are transported from where their concentration is low to where their concentration is high.)

Which line represents the bag that contained a solution isotonic to the 0.6 molar solution at the beginning of the experiment?

C

Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?

The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.

A patient has had a serious accident and lost a lot of blood. In an attempt to replenish body fluids, distilled water, equal to the volume of blood lost, is transferred directly into one of his veins. What will be the most probable result of this transfusion?

The patient's red blood cells will swell because the blood fluid is hypotonic compared to the cells.

If you examine side A after 3 days, you should find

a decrease in the concentration of NaCl and a decrease in the water level.

This is an animation of _____. (Circle thingy that forces itself out the plasma membrane)

exocytosis (A membranous vesicle is fusing with the plasma membrane and releasing its contents into the extracellular fluid.)

Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are

hypertonic to fresh water but hypotonic to the salt solution.

Endocytosis moves materials _____ a cell via _____.

into ... membranous vesicles (The prefix "endo-" means "inward.")

A cell whose cytoplasm has a concentration of 0.02 molar glucose is placed in a test tube of water containing 0.02 molar glucose. Assuming that glucose is not actively transported into the cell, which of the following terms describes the tonicity of the external solution relative to the cytoplasm of the cell?

isotonic

Initially, in terms of tonicity, the solution in side A with respect to that in side B is

isotonic.

This is an animation of _____. (Brown thing gets sucked into the plasma membrane)

phagocytosis (Phagocytosis involves the engulfing of large particles.)

A white blood cell engulfing a bacterium is an example of _____.

phagocytosis (Phagocytosis occurs when a cell engulfs a large particle.)

You know that this process is _____ because _____.

pinocytosis ... the cell is engulfing extracellular fluid (Pinocytosis is "cell drinking.")

This is an animation of _____. (receptor protein)

receptor-mediated endocytosis (A receptor protein is involved in this process.)

At the beginning of the experiment,

side A is hypotonic to side B.

You are working on a team that is designing a new drug. In order for this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule enters the cell?

similarity of the drug molecule to other molecules transported by the target cells