Chapter 5.2

What would happen if the plasma membrane were composed solely of phospholipids and no proteins?

Simple diffusion and osmosis would continue to occur.

Which of these statements is TRUE with regard to this animation?

Sodium and potassium ions are transported against their concentration gradients.

What causes a plant to wilt?

The cells lose turgor pressure.

If red blood cells are taken from the body and placed in a hypertonic solution, what happens to the cells?

The cells shrivel up because water leaves them.

What happens when diffusion moves molecules across the plasma membrane?

The process is relatively slow and is driven by concentration gradients.

Imagine that you fill a shallow tray with water and place a drop of red ink in one end of the tray and a drop of green ink in the other end. Which of the following is TRUE at equilibrium?

The red and green inks are both uniformly distributed throughout the tray.

Cells use exocytosis to

The release of substances from a cell

If the cytoplasmic fluid of cells in a houseplant were to become very salty, what would happen inside those cells?

The vacuoles would shrivel, but the cells would maintain turgor pressure.

What do channel proteins, aquaporins, and carrier proteins have in common?

They all perform facilitated diffusion.

Osmosis is the diffusion of water molecules across selectively permeable membranes. True or False?

True

Imagine an artificial cell made with a selectively permeable membrane that allows water to pass through but does not allow sugar to pass. If the artificial cell contains a 1% sugar solution and then you place the cell in a 2% sugar solution, what happens?

Water leaves the cell because the solution is hypertonic to the cell.

Two aqueous solutions are separated by a selectively permeable membrane that allows water to pass through but does not allow starch to pass through. Solution A is 10% starch and solution B is 5% starch. What will occur?

Water will diffuse from solution B to solution A.

The bacterium Vibrio cholerae releases a toxin that blocks a channel protein in the membranes of cells that line the intestine. This toxin prevents the movement of sodium ions from the inside of the intestine into cells. If the sodium ions could not move into the cells, how would this affect the movement of water between the inside of the intestine and the cells?

Water would leave the cells and enter the intestines by osmosis.

The cytoplasm of a certain cell, such as a neuron, already has a high concentration of K+ ions. How can K+ ions continue to enter the cell?

active transport

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

Which of the following is an energy-requiring mode of transport that brings substances into a cell?

active transport

Which of the following requires adenosine triphosphate?

active transport

Active transport requires all of the following EXCEPT

aquaporins

Which of the following would be likely to raise the concentration of calcium ions in a cell?io

blocking ATP binding sites

Carbon dioxide crosses the plasma membrane by simple diffusion. The rate at which carbon dioxide enters the cell is determined by the

concentration of carbon dioxide on each side of the membrane.

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

Which of the following occurs as an enzyme produced by a cell is secreted from the cell?

exocytosis

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

facilitated diffusion

Glucose is a six-carbon sugar that 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. Given this information, which transport mechanism is most probably functioning in the intestinal cells?

facilitated diffusion

Molecules assisted by carrier proteins may cross a selectively permeable membrane by

facilitated diffusion

Which type of transport requires assistance from membrane proteins, but no energy?

facilitated diffusion

Based on these four illustrations of diffusion, which mode would most likely be used to transport oxidized zinc (which has a charge of +2) through the cell membrane?

facilitated diffusion through channel proteins

A freshwater protozoan, such as Paramecium, tends to ________ because it lives in a ________ environment.

gain water; hypotonic

For diffusion to occur, there must be

gradient

This cell is in a(n) _____ solution.

hypertonic

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

hypertonic solution ... lost water

The blood plasma of a man who drinks salt water will become ________ to his red blood cells, whereas the red blood cells will be ________ to the blood plasma.

hypertonic, hypotonic

Solutions that cause water to enter cells by osmosis are called

hypotonic

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

hypotonic ... swelled

Endocytosis moves materials _____ a cell via _____.

into ... membranous vesicles

Osmosis moves water from a region of

low solute concentration of to a region of high solute concentration

What is active transport?

movement of molecules into or out of a cell against a concentration gradient

In reference to diffusion, passive really means

no energy required

To say that a cell is "selectively permeable" means

only certain molecules can pass through

The diffusion of water molecules across a selectively permeable membrane is called

osmosis

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

osmosis

Facilitated diffusion is a type of _____.

passive transport

When substances move across a plasma membrane and down concentration gradients, this is called

passive transport

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

phagocytosis

Some white blood cells in the human body are able to engulf bacteria and destroy them. What should this engulfing process be called?

phagocytosis

The process in which white blood cells engulf bacteria is termed

phagocytosis

Which process accounts for the movement of solid particles (such as food) into some animal cells?

phagocytosis

Endocytosis

process by which a cell takes material into the cell by infolding of the cell membrane

What simple property causes molecules to diffuse from high concentration toward a lower concentration?

random motion of molecules

Which method of transport can a cell use to bring in molecules without allowing them to pass through the plasma membrane?

receptor-mediated endocytosis

Molecules that permeate a plasma membrane by facilitated diffusion

require the aid of transport proteins

The gases O2 and CO2 enter or leave a plant cell by

simple diffusion

Structure A is a _____.

solute

If a frog egg cell is placed into a hypotonic solution, it will

swell via osmosis

You can recognize the process of pinocytosis when _____.

the cell is engulfing extracellular fluid

All of the following may influence the rate of simple diffusion across a selectively permeable membrane EXCEPT the

the size of the cell

The rate of facilitated diffusion of a molecule across a membrane will increase as the concentration gradient of the molecule across the membrane increases to a certain point. Eventually, an increase in the concentration of the molecule will not cause any further increase in facilitated diffusion. Thus, there is a maximal rate of facilitated diffusion. This is because

there are a limited number of carrier proteins in the membrane.

Water crosses the plasma membrane

through facilitated diffusion or diffusion.

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

transport protein

Structure B is a _____.

transport protein

Which of the following types of membrane proteins are responsible for facilitated diffusion?

transport proteins

If you forget to water your favorite plant, all of the following will occur at a cellular level EXCEPT

turgor pressure will build up in the cell.

A cell has no membrane proteins at all. Which substance will diffuse across the membrane fastest?

Oxygen

The net movement of water or other molecules across a membrane from a region of higher concentration to a region of lower concentration is best described by which of the following?

Passive transport

As a cell gets larger, which measurement of the cell increases the fastest?

volume

When can a cell transport a molecule across the cell membrane without expending energy

when the molecule is more concentrated outside the cell

If the radius of one cell were twice as large as the radius of another cell, how much higher or lower would its surface-area-to-volume ratio be?

1/2

Why can't cells get as large as golf balls?

A cell would not have enough surface area

Imagine that beaker A has a 10% sucrose solution, and beaker B has an 8% sucrose solution. This means that

Beaker A is hypertonic relative to beaker B.

Two similar-sized animal cells are placed in a 0.5% sucrose solution. Cell A enlarges for a while and then stops; cell B continues to enlarge and finally ruptures. Which of the following must have been TRUE at the beginning of the experiment?

Cell B has a higher concentration of sucrose than cell A.

Cell A has no membrane proteins at all. Cell B has aquaporin membrane proteins. Both cells are placed in a hypertonic solution. What will happen?

Cell B shrivels faster than cell A

In active transport,

Energy-requiring process that moves material across a cell membrane against a concentration difference

The secretion of excess water via a contractile vesicle of a Paramecium cell is an example of

Exocytosis

More than half a century ago, two cell biologists published details of their research involving isolated membrane vesicles from chloroplasts. Normally, the fluid inside these vesicles is near neutral. In an experiment, these membrane vesicles were soaked in an acidic solution (pH 4) until the inside of the vesicle also became pH 4. Based on the details provided in this scenario, by what mechanism could hydrogen ions have crossed the vesicle membrane, and what do you think happened at the molecular level?

Facilitated diffusion; hydrogen ions moved into the vesicle through a channel.

After a dye diffuses uniformly throughout a glass of water, the dye molecules are no longer moving. True or False?

False

Carrier molecules in the plasma membrane are required only for active transport.

False

Which direction is water most likely to move if there is a membrane or concentration difference between two regions?

Hypotonic to hypertonic

Suppose you have two glucose solutions separated by a selectively permeable membrane. If there is a concentration gradient of glucose across the membrane, then the solutions cannot be ________ relative to each other.

Isotonic

How does a freshwater Paramecium counteract osmosis

It pumps salt into a contractile vacuole, drawing excess water in to be squeezed out of the cell.

Vibrio cholerae causes severe diarrhea in its victims. How might it cause this to occur?

It tricks the cells of the intestines into secreting ions.

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

Lipid soluble molecule

Diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration.

Cells are rarely large enough to be visible due to restrictions of area/volume. How then can neuron cells reach lengths of up to several feet?

Neurons have more surface area than spherical cells because they are long and thin.