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Mastering Biology Chapter 7 Answers

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The difference between pinocytosis and receptor-mediated endocytosis is that _____.
pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity
Endocytosis moves materials _____ a cell via _____.
into … membranous vesicles
You can recognize the process of pinocytosis when _____.
the cell is engulfing extracellular fluid
An animal cell lacking carbohydrates on the external surface of its plasma membrane would likely be impaired in which function?
cell-cell recognition
When a cell is in equilibrium with its environment, which of the following processes occurs for substances that can diffuse through the plasma membrane?
There is random movement of substances into and out of the cell.
Some solutes pass readily through the lipid bilayer of a cell membrane, whereas others pass through much more slowly, or not at all.
-Small nonpolar (hydrophobic) molecules, such as dissolved gases (O2, CO2, N2) and small lipids, can pass directly through the membrane. They do so by interacting directly with the hydrophobic interior of the lipid bilayer.
-Very small polar molecules such as water and glycerol can pass directly through the membrane, but much more slowly than small nonpolar molecules. The mechanism that permits small polar molecules to cross the hydrophobic interior of the lipid bilayer is not completely understood, but it must involve the molecules squeezing between the hydrophobic tails of the lipids that make up the bilayer.
-Polar molecules such as glucose and sucrose have very limited permeability.
-Large molecules such as proteins cannot pass through the lipid bilayer.
-Ions and charged molecules of any size are essentially impermeable to the lipid bilayer because they are much more soluble in water than in the interior of the membrane.
Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism? Select all that apply.
water, oxygen, carbon dioxide, lipids
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.
In what way do the membranes of a eukaryotic cell vary?
Certain proteins are unique to each membrane.
Which of the following statements is TRUE with regard to this animation?
Both sodium and potassium ions are transported against their concentration gradients.
Which of the following membrane activities requires energy from ATP hydrolysis?
Na+ ions moving out of the cell
Several epidemic microbial diseases of earlier centuries incurred high death rates because they resulted in severe dehydration due to vomiting and diarrhea. Today they are usually not fatal because we have developed which of the following types of treatments?
Hydrating drinks that include high concentrations of salts and glucose
Facilitated diffusion is a type of _______.
passive transport
An organism with a cell wall would most likely be unable to take in materials through _____.
Which of the following types of molecules are the major structural components of the cell membrane?
phospholipids and proteins
The presence of cholesterol in the plasma membranes of some animals
enables the membrane to stay fluid more easily when cell temperature drops.
Which of the following is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold?
by increasing the percentage of unsaturated phospholipids in the membrane
In order for a protein to be an integral membrane protein it would have to be which of the following?
When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are
integral proteins
Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?
The double bonds form kinks in the fatty acid tails, forcing adjacent lipids to be further apart.
Of the following functions, which is most important for the glycoproteins and glycolipids of animal cell membranes?
a cell’s ability to distinguish one type of neighboring cell from another
An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function?
cell-cell recognition
Which of these are not embedded in the lipid bilayer at all?
peripheral proteins
Which of these often serve as receptors or cell recognition molecules on cell surfaces?
What kinds of molecules pass through a cell membrane most easily?
small and hydrophobic
Which of the following is a characteristic feature of a carrier protein in a plasma membrane?
It exhibits a specificity for a particular type of molecule.
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?
Which of the following statements is correct about diffusion?
It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
Water passes quickly through cell membranes because
it moves through aquaporins in the membrane.

Cystic fibrosis is a genetic disease in humans in which chloride ion channels in cell membranes are missing or nonfunctional.

Chloride ion channels are membrane structures that include which of the following?

hydrophilic proteins
Which of the following factors does not affect membrane permeability?
The polarity of membrane phospholipids
How can a lipid be distinguished from a sugar?
Lipids are mostly nonpolar.
True or false? Osmosis is a type of diffusion.
What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?
Amphipathic nature
Which of the following particles could diffuse easily through a cell membrane?
Oxygen (O2)
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.
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?
Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are
hypertonic to fresh water but hypotonic to the salt solution.
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.
Which of the following membrane activities require energy from ATP hydrolysis?
Na+ ions moving out of the cell
What are the membrane structures that function in active transport?
integral proteins
Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. Using this information, which transport mechanism is most probably functioning in the intestinal cells?
facilitated diffusion
What is the voltage across a membrane called?
membrane potential
The sodium-potassium pump is called an electrogenic pump because it
contributes to the membrane potential.
The movement of potassium into an animal cell requires
an energy source such as ATP or a proton gradient.
White blood cells engulf bacteria through what process?
In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis?
on the inside surface of the vesicle
Which of the following factors would tend to increase membrane fluidity?
a greater proportion of unsaturated phospholipids

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

A) phagocytosis
B) osmosis
C) passive transport
D) pinocytosis
E) diffusion

B) Osmosis is the passive transport of water

If there is a greater concentration of solute on the outside if the cell, it is considered to be what type of solution?

A) isotonic
B) hypertonic or isotonic
C) hypertonic
D) hypotonic and isotonic
E) hypotonic


The permeability of a biological membrane to a specific polar solute may depend on which of the following?

A) the amount of cholesterol in the membrane
B) the types of transport proteins in the membrane
C) the phospholipid composition of the membrane
D) the presence of unsaturated fatty acids in the membrane
E) the types of polysaccharides present in the membrane

B) 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

According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly

A) spread in a continuous layer over the inner and outer surfaces of the membrane.
B) free to depart from the fluid membrane and dissolve in the surrounding solution.
C) embedded in a lipid bilayer.
D) randomly oriented in the membrane, with no fixed inside-outside polarity.
E) confined to the hydrophobic interior of the membrane.


Which of the following factors would tend to increase membrane fluidity?

A) a lower temperature
B) a relatively high protein content in the membrane
C) a greater proportion of unsaturated phospholipids
D) a greater proportion of saturated phospholipids
E) a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses


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

A) Active transport is usually down the concentration gradient of the solute, whereas passive transport is always against the concentration gradient of the solute.
B) Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy.
C) Active transport is always faster than passive transport.
D) Active transport uses protein carriers, whereas passive transport uses carbohydrate carriers.
E) Active transport is used for ions, passive transport is used for uncharged solutes

B) Active and passive transport can be distinguished by whether or not they use cellular energy.

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

A) receptor-mediated endocytosis
B) passive diffusion of the glucose through the lipid bilayer
C) movement of glucose into the cell through a glucose channel
D) facilitated diffusion of the glucose using a carrier protein
E) cotransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis

E) 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 white blood cell engulfing a bacterium is an example of _____.

A) phagocytosis
B) exocytosis
C) pinocytosis
D) receptor-mediated endocytosis
E) facilitated diffusion

A) Phagocytosis occurs when a cell engulfs a large particle.

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

A) Transport proteins organize the phospholipids to allow the solute to cross the membrane.
B) Transport proteins provide a low-resistance channel for water molecules to cross the membrane.
C) Transport proteins provide a hydrophilic route for the solute to cross the membrane.
D) Transport proteins provide a protein site for ATP hydrolysis, which facilitates the movement of a solute across a membrane.
E) Transport proteins provide the energy for diffusion of the solute

C) This is the most general description of facilitated diffusion by membrane transport proteins

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?

A) passive transport
B) diffusion
C) active transport
D) osmosis
E) facilitated diffusion

C) For the cell to accumulate phosphate, it must move calcium against the concentration gradient. This process requires energy

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