Ch 7

Which of these can RAPIDLY pass directly through the phospholipids of the plasma membrane, without the help of a transport protein?

A only; Small, nonpolar, lipid-soluble molecules can pass rapidly through the phospholipids of the plasma membrane. Ions, such as hydrogen ions, and hydrophilic molecules, such as water and glucose, cannot rapidly pass directly through the phospholipids of the membrane. To move rapidly through the membrane, they must pass through membrane transport proteins.

Active and passive transport of solutes across a membrane typically differ in which of the following ways?

Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy; Active and passive transport can be distinguished by whether or not they use cellular energy.

If the concentration of phosphate in the cytosol is 2.0 mM and the concentration of phosphate in the surrounding fluid is 0.1 mM, how could the cell increase the concentration of phosphate in the cytosol?

Active transport; For the cell to accumulate phosphate, it must move calcium against the concentration gradient. This process requires energy.

What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?

Amphipathic nature; Detergents form micelles around the grease, which are then washed away because the polar head groups facing outward on the micelle are water-soluble.

According to the fluid mosaic model of cell membranes, phospholipids . . .

Can move laterally along the plane of the membrane.

Which of the following is least likely to be important in holding the components of a biological membrane together?

Covalent interactions between the phospholipid and protein components of the membrane; This is not an important interaction because there are rarely covalent bonds between the phospholipids and integral membrane proteins.

Which of the following correctly describes some aspect of exocytosis or endocytosis?

Exocytosis and endocytosis temporarily change the surface area of the plasma membrane; The fusion or budding of transport vesicles at the plasma membrane either adds or removes proteins and phospholipids, thus temporarily changing the surface area.

If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?

Hypotonic; The salt concentration in the solution is lower than it is in the cell, so water enters the cell, causing it to burst.

Which of the following statements correctly describes osmosis?

In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration

The membranes of winter wheat are able to remain fluid when it is extremely cold by . . .

Increasing the proportion of unsaturated phospholipids in the membrane.

Which of the following statements describes a characteristic feature of a carrier protein in a plasma membrane?

It exhibits specificity for a particular type of molecule.

Which of the following statements about diffusion is true?

It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration

Hydrophobic substances like salad oil are . . .

Nonpolar molecules that repel water molecules; If you had trouble with this question, review the following material: Salad oil is predominantly made up of carbon and hydrogen atoms, which share electrons almost equally, forming nonpolar covalent bonds. Substances that are nonpolar due to their large number of nonpolar bonds do not have an affinity for water and are termed hydrophobic ("water-fearing"). Substances that contain polar bonds are hydrophilic ("water-loving") because they contain atoms with partial charges due to those polar bonds. For example, a hydrogen atom with a partial positive charge can form a hydrogen bond with a partial negative charge on the oxygen atom of a water molecule.

Which of the following would likely diffuse through the lipid bilayer of a plasma membrane most rapidly?

O2

Which of the following particles could diffuse easily through a cell membrane?

Oxygen (O2); Small nonpolar molecules such as oxygen can diffuse across cell membranes.

Facilitated diffusion is a type of

Passive transport; During facilitated diffusion, the cell is not expending energy to move the particles across the membrane; therefore, facilitated diffusion is a form of passive transport.

The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same.

Side A is hypotonic to side B

What kinds of molecules pass through a cell membrane most easily?

Small and hydrophobic

If the pores in the selectively permeable membrane became larger, but still not large enough to let the sugar pass through, what would happen during osmosis in the U-shaped tube compared to what is shown in the figure?

The final water levels would be the same as shown in the figure, but the solutions would reach near equal concentrations faster; The relative concentrations of solutes and free water on either side of the membrane determines the amount of osmosis, but the size of the pores determines how fast osmosis occurs.

Phospholipids have a hydrophilic head and hydrophobic tails.

The hydrophilic head includes a glycerol molecule attached to a single phosphate group, which is then attached to another small molecule. The phosphate group and its attachments are either polar or charged. Water molecules are polar and therefore are attracted to these charged regions of the phospholipid head. The hydrophobic tails are two fatty acids attached to the glycerol molecule of the head. Water molecules are not attracted to the tails because C-H bonds are relatively nonpolar and therefore do not result in charged regions in the tails.

How do membrane phospholipids interact with water?

The polar heads interact with water; the nonpolar tails do not; If you had trouble with this question, review the following material: A phospholipid is similar to a fat molecule but has only two fatty acids attached to glycerol rather than three. The third hydroxyl group of glycerol is joined to a phosphate group, which has a negative electrical charge in the cell. The fatty acids, referred to as the "tails" of the phospholipid, are hydrocarbons that are hydrophobic and therefore do not interact with water. The phosphate group and its attachments form a hydrophilic "head" that has an affinity for water.

Which of the following statements about osmosis is correct?

The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis; Aquaporins facilitate water movement across membranes and thus speed up the process of osmosis.

Which of the following statements about a typical plasma membrane is correct?

The two sides of the plasma membrane have different lipid and protein composition; Because the membrane serves different functions on the cytoplasmic and exterior surfaces, the structure and composition of the surfaces must be different.

The permeability of a biological membrane to a specific polar solute depends primarily on which of the following?

The types of transport proteins in the membrane; The lipid bilayer will be impermeable or very poorly permeable to polar or charged solutes. The presence of the correct transport protein will determine the permeability.

If more sugar were added to the solution on the left side of the tube, what would happen to the water level on the right side of the tube?

The water level would go down; If more solute were added on the left side, it would draw more water to cluster around the solute molecules, lowering the free water on the left compared to the right side. That would cause osmosis of water toward the left side, lowering the water level on the right side.

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

Transport protein; The protein is allowing solute molecules to enter the cell.

In facilitated diffusion, what is the role of the transport protein?

Transport proteins provide a hydrophilic route for the solute to cross the membrane; This is the most general description of facilitated diffusion by membrane transport proteins.

True or false? Osmosis is a type of diffusion.

True; Osmosis is the diffusion of water across a selectively permeable membrane.

True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group.

True; The hydrophilic, or water-loving, portion of a phospholipid is the polar head, whereas the hydrophobic portion is the nonpolar tail.

Which of the following best describes the structure of a biological membrane?

Two layers of phospholipids with proteins either crossing the layers or on the surface of the layers; The membrane proteins can be found either embedded in or attached to the surface of the phospholipid bilayer.

Which of the following statements about the conditions shown in the U-shaped tube are true?

Water is tightly clustered around the hydrophilic solute molecules on both sides of the membrane. There is less free water in the right arm of the tube than in the left arm of the tube; Water molecules will cluster around hydrophilic solute molecules (shown as green dots), leaving less water "free" in the solution. There is more solute in the right arm of the tube, so there is less free water on that side.

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

a

If you are going to bake potatoes, and your potatoes are soft and dehydrated, they can be soaked in __________ to make them more firm before baking.

a hypotonic solution such as tap water

A cell that neither gains nor loses water while sitting in a solution is probably sitting in

an isotonic environment.

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

Five dialysis bags, constructed of a type of membrane that is permeable to water and impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed), and the percent change in mass of each bag was graphed. Which line in the graph represents the bag that contained a solution isotonic to the 0.6 M solution at the beginning of the experiment?

c

An animal cell lacking carbohydrates on the external surface of its plasma membrane would likely be impaired in which function?

cell-cell recognition

Phospholipids vary in the small molecules attached to the phosphate group. The phospholipid shown in the figure has a____ attached to phosphate.

choline group

The movement of glucose into a cell against a concentration gradient is most likely to be accomplished by which of the following?

cotransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis; Movement of most solutes against their concentration gradient couples the movement of one solute down its concentration gradient to the movement of another (glucose in this case) against its concentration gradient.

A phospholipid also has two "tails" made up of two____molecules, which consist of a carboxyl group with a long hydrocarbon chain attached.

fatty acid

During osmosis, water diffuses across a selectively permeable membrane from the region of higher ___ concentration and lower ___concentration to the side with lower ___concentration and higher ___concentration.

free water __ solute __ free water __ solute

Paramecium is a genus of protists that lives in water. It has organelles called contractile vacuoles that continually eliminate the excess water gained through osmosis. Knowing that Paramecia gain water through osmosis, we can deduce that they normally live in

freshwater lakes and ponds

Because the phosphate group and its attachments are either charged or polar, the phospholipid head is____, which means it has an affinity for water.

hydrophilic

Because the C-H bonds in the fatty acid tails are relatively nonpolar, the phospholipid tails are____, which means they are excluded from water.

hydrophobic

You know that this cell is in a(n) _____ solution because it _____.

hypertonic solution ___ lost water; A cell will lose water when placed in a hypertonic solution

This cell is in a(n) ____ solution

hypertonic; There is a greater concentration of solute outside the cell.

You know that this cell is in a(n) _____ solution because the cell _____.

hypotonic ___swelled; Acell will gain water placed in a hypotonicsolution.

Celery stalks that are immersed in fresh water for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the fresh water_____.

is hypotonic and the salt solution is hypertonic to the cells of the celery stalks

A human cell placed into a hypertonic solution is likely to

lose water by osmosis

When molecules move down their concentration gradient, they move from where they are ____to where they are ____

more concentrated; less concentrated

What name is given to the process by which water crosses a selectively permeable membrane?

osmosis; Osmosis is the passive transport of water.

Diffusion across a biological membrane is called

passive transport

A phospholipid has a "head" made up of a glycerol molecule attached to a single____which is attached to another small molecule.

phosphate group

When a person is dehydrated, his or her IV fluids

should be isotonic, because either a hypertonic or hypotonic IV would damage red blood cells

Structure A is a ___

solute; a solute is crossing the plasma membrane.

A human cell placed in a hypotonic environment would

take up water through osmosis.

Many bacteria and fungi have a difficult time surviving on our food if the food is very salty. The best explanation for this is

that the salt in the food creates a hypertonic environment for the bacteria and fungi.

What will happen to a red blood cell (RBC), which has an internal ion content of about 0.9%, if it is placed into a beaker of pure water?

the cell would swell because the water in the beaker is hypotonic relative to the cytoplasm of the RBC

Structure B is a ___

transport protein; the transport protein facilitates the moement of the solute across the plasma membrane