6. The Membrane

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

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

Which of the following statements about diffusion is true?

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 __________.

Which of these statements describes some aspect of facilitated diffusion?

Which of the following is false in regard to facilitated diffusion?

Based on Figure 7.18, which of these experimental treatments would increase the rate of sucrose transport into a plant cell? a. decreasing extracellular sucrose concentration b. decreasing extracellular pH c. decreasing cytoplasmic pH d. adding a substance that makes the membrane more permeable to hydrogen ions

Draw and label the plasma membrane of a cell that is placed in a solution with concentrations of calcium ions and lactose that are greater than those on the inside of the cell. Use arrows to show the relevant gradients and the activity of the following membrane proteins: (1) a pump that exports protons; (2) a calcium channel; and (3) a lactose carrier.

In terms of structure, how do channel proteins differ from carrier proteins?

Facilitated diffusion across a membrane requires ______________ and moves a solute ______________ its concentration gradient. a. transport proteins . . . up (against) b. transport proteins . . . down c. energy and transport proteins . . . up d. energy and transport proteins . . . down

Cells lining kidney tubules function in the reabsorption of water from urine. In response to chemical signals, they reversibly insert additional aquaporins into their plasma membranes. In which of these situations would your tubule cells have the most aquaporins: after a long run on a hot day, right after a large meal, or after drinking a large bottle of water? Explain.

SCIENTIFIC THINKING Mercury is known to inhibit the permeability of water channels. To help establish that the protein isolated by Agre's group was a water channel, the researchers incubated groups of RNA-injected oocytes (which thus made aquaporin proteins) in four different solutions: plain buffer, low concentration and high concentration of a mercury chloride (HgCl2) solution, and low concentration of a mercury solution followed by an agent (ME) known to reverse the effects of mercury. The water permeability of the cells was determined by the rate of their osmotic swelling. Interpret the results of this experiment, which are presented in the graph below. Control oocytes not injected with aquaporin RNA were also incubated with buffer and the two concentrations of mercury. Predict what the results of these treatments would be