Membrane Structure/Function

Which of these is hydrophobic like the interior of the plasma membrane?

A (Lipid soluble molecules are hydrophobic)

Which of the following is an accurate comparison of active transport and facilitated diffusion?

Active transport moves solutes against their concentration gradient; facilitated diffusion moves substances down their concentration gradient. Submit

Using the data from the graphs and what you know about membranes and metabolic pathways, predict which of the following is the likely reason why actions of aquaporins in a membrane can change so rapidly.

Aquaporins are inserted into the membrane as needed.

Cells A and B are the same size and shape, but cell A is metabolically quiet and cell B is actively consuming oxygen. Oxygen will diffuse more quickly into cell _____ because _____.

B ... the diffusion gradient there is steeper Submit (As long as a metabolically active cell consumes oxygen as it enters, diffusion into the cell will continue because the concentration gradient favors movement in that direction)

Which of these statements describes what occurs in facilitated diffusion?

Facilitated diffusion of solutes occurs through protein pores in the membrane.

How do fatty acids travel through a cell membrane?

carrier proteins

What condition might result from an excess of aquaporins?

fluid retention in pregnant women

Some protozoans have special organelles called contractile vacuoles that continually eliminate excess water from the cell. The presence of these organelles tells you that the environment

is hypotonic to the protozoan.

In active transport,

molecules move across the plasma membrane against their concentration gradient.

You're on the pilot episode of a new game show called "The Transport Factor." The host hands you three different amino acids, four different sugars, and two different ions. Then the host shouts, "How many different proteins does the cell need to move these molecules across the plasma membrane using facilitated transport?" Quickly, you correctly respond: _____.

nine (The specificity of transport proteins for the materials they transport is exactly like the specificity of enzymes for their substrates. Therefore, if there are nine different substances to be transported by facilitated diffusion, this almost certainly involves nine different transport proteins.)

Overall, membranes seem to have a great deal in common, but on closer inspection it is revealed that membranes of different cells have unique properties. What is the primary component of membranes that gives membranes cell-specific properties?

proteins (There is a large variety of proteins, and it is differences in these widely varying molecules that give a particular membrane its unique properties.)

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

receptor-mediated endocytosis

Which characteristic promoted the utilization of lipids as the first cell membrane?

self-assembly into a simple membrane

The lipids in a cell membrane are arranged _____.

so that the nonpolar parts of two lipids point toward each other(A phospholipid bilayer can exist as a stable boundary between two aqueous compartments because the molecular arrangement shelters the hydrophobic tails of the phospholipids from water while exposing the hydrophilic heads to water.)

What controls the net direction of molecules, such as oxygen, involved in passive transport?

the direction of the oxygen concentration gradient Submit (The direction a material moves in passive transport is determined by the material's concentration gradient, with material diffusing from regions of higher concentration to regions of lower concentration)

Plasma membranes are selectively permeable. This means that

the plasma membrane allows some substances to enter or leave a cell more easily than others.

Water crosses the plasma membrane

through facilitated diffusion or diffusion.

Structure A in the figure is a(n) _____.

transport protein (The protein is allowing solute molecules to enter the cell)

Aquaporins are proteins that facilitate the transport of __________ across the membrane.

water (Aquaporins are a newly discovered class of transport proteins that transport water in cells with very high water permeability needs.)

A group of single-cell organisms collected from the ocean was brought into the lab for examination. The lab assistant was concerned that the water had become full of toxic waste products and so added clean water to the culture. All of the organisms died, and when she looked at them under the microscope, all she could see were bits and pieces of them scattered throughout the water. What likely happened?

She added water that was hypotonic to the culture of organisms, and they ruptured.

The concentration of solutes in a red blood cell is about 2%. 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 (Water moves by osmosis from the hypotonic environment, the cell interior, to the hypertonic environment.)

The sodium-potassium pump uses energy from ATP to move sodium ions out of the cell, and potassium ions into the cell. This is an example of

active transport.

The fluid mosaic model describes the plasma membrane as consisting of

diverse proteins embedded in a phospholipid bilayer. Submit

The plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell. This describes the process of

endocytosis.

A molecule moves down its concentration gradient using a transport protein in the plasma membrane. This is an example of

facilitated diffusion.