456 #2

Which of the following substances would have the most trouble crossing a biological membrane by diffusing through the lipid bilayer?

Na+

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?

Protein

Osmosis is often viewed incorrectly as a process driven directly by differences in solute concentration across a selectively permeable membrane. What really drives osmosis?

The difference in water concentration across a selectively permeable membran

What controls the direction of a molecule, such as oxygen, involved in passive transport?

The direction of the oxygen concentration gradient

Which of the following statements regarding membrane function is false?

The plasma membrane is the control center of the cell.

In the lab, you use a special balloon that is permeable to water, but not sucrose, to make an "artificial cell." The balloon is filled with a solution of 20% sucrose and 80% water and is immersed in a beaker containing a solution of 40% sucrose and 60% water. Which of the following will occur?

Water will leave the balloon

Utah's Great Salt Lake has an average salinity seven times higher than that of the oceans. Very few multicellular organisms live in this harsh environment. An example is the brine shrimp, which must devote a large portion of its metabolic energy to osmoregulation. These brine shrimp must _____.

actively pump water back into their cells to counter its loss due to osmosis

Membrane phospholipids

are able to drift in the plasma membrane

Small, nonpolar, hydrophobic molecules such as fatty acids

easily pass through a membrane's lipid bilayer

When two aqueous solutions that differ in solute concentration are placed on either side of a semipermeable membrane and osmosis is allowed to take place, the water will

exhibit a net movement to the side with lower water concentration

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.

Diffusion does not require the cell to expend ATP. Therefore, diffusion is considered a type of

passive transport

Most of the functions of a cell membrane, including transport and enzymatic function, are performed by

proteins

When placed in a hypotonic environment, where the solute concentration is below that of the cell, a houseplant will _____.

remain standing upright

All cells are enclosed by a plasma membrane that is similar in ________ and ________.

structure . . . function

Osmosis can be defined as

the diffusion of water across a membrane.

Plasma membranes are selectively permeable. This means that

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

If placed in tap water, an animal cell will undergo lysis, whereas a plant cell will not. What accounts for this difference?

the relative inelasticity and strength of the plant cell wall

If you shut the system off and pressure was no longer applied to Tank A, you would expect After reading the paragraph, answer the question(s) that follow. Americans spend up to $100 billion annually for bottled water (41 billion gallons). The only beverages with higher sales are carbonated soft drinks. Recent news stories have highlighted the fact that most bottled water comes from municipal water supplies (the same source as your tap water), although it may undergo an extra purification step called reverse osmosis. Imagine two tanks that are separated by a membrane that's permeable to water, but not to the dissolved minerals present in the water. Tank A contains tap water and Tank B contains the purified water. Under normal conditions, the purified water would cross the membrane to dilute the more concentrated tap water solution. In the reverse osmosis process, pressure is applied to the tap water tank to force the water molecules across the membrane into the pure water tank. If you shut the system off and pressure was no longer applied to Tank A, you would expect

the water to reverse flow from Tank B to Tank A.