Bio 101: 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. (Active transport involves moving solutes against their concentration gradient. Facilitated diffusion moves solutes down their concentration gradient. Active transport requires the use of ATP, whereas facilitated diffusion does not. )

Water movement is important in urine formation in the kidneys. Urine is formed when the blood is filtered by the kidneys into kidney tubules. Three figures are presented here that relate to how the kidney tubules respond to the administration of the hormone vasopressin. The direction that water flows in these figures is from the kidney tubules back into the blood. 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 (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.)

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.

How do fatty acids travel through a cell membrane?

carrier proteins

The fluid mosaic model describes the plasma membrane as consisting of

diverse proteins embedded in a phospholipid bilayer.

What condition might result from an excess of aquaporins?

fluid retention in pregnant women ( Aquaporins transport water. An excess of aquaporins during pregnancy can result in fluid retention.)

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. (Molecules move against their concentration gradient in active transport.)

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 (In receptor-mediated endocytosis, only a specific molecule, called a ligand, can bind to the receptor. Without receptor binding occurring first, endocytosis does not proceed.)

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 (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. (Water can cross the plasma membrane through the process of facilitated diffusion. However, water molecules can also cross the lipid bilayer directly.)

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.)

Which of these statements describes what occurs in facilitated diffusion?

Facilitated diffusion of solutes occurs through protein pores in the membrane. ( Protein pores are passageways for facilitated diffusion.)

Water movement is important in urine formation in the kidneys. Urine is formed when the blood is filtered by the kidneys into kidney tubules. Three figures are presented here that relate to how the kidney tubules respond to the administration of the hormone vasopressin. The direction that water flows in these figures is from the kidney tubules back into the blood. How do the data in Figure A relate to the data in Figures B and C?

Figure C is essentially a summary of the data in Figure A.

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 sodium-potassium pump moves ions across the plasma membrane against their concentration gradients. This requires energy and is an example of active transport.)

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. (In endocytosis, the plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell.)

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

facilitated diffusion. (In facilitated diffusion, molecules use a transport protein to move across the plasma membrane. There is a net movement of molecules down the concentration gradient -- that is, there is a net movement of molecules from where they are more concentrated to where they are less concentrated.)