Cell Volume Regulation

Question 1

In discussions of cell volume changes, we consider only

Answer 1

fluctuations in water content.

Question 2

Water diffuses in a given direction in order to equilibrate differences in _____

Answer 2

osmolarity

Question 3

If the osmolarity outside of a cell is greater than the osmolarity inside the cell,

Answer 3

water will diffuse out of the cell and the cell will shrink.
In this case, the extracellular fluid is said to be hyper osmotic and hypertonic to the cell

Question 4

If the osmolarity of a cell is less than the osmolarity inside the cell,

Answer 4

water will diffuse into the cell and the cell will swell.

In this case, the extracellular fluid is said to be hypo osmotic and hypotonic to the cell

Question 5

List the three mechanisms that different cells have evolved to keep from swelling and bursting.

Answer 5

1. make the cell membrane membrane impermeable to water
   a. creates a problem for growing cells
2. build a strong cell wall
   a. applies hydrostatic force to counter osmotic force
   b. requires significant forces and limit allowed cell shapes
3. balance osmotic force by having solute molecule in the extracellular fluid
   a. functions to equilibrate the osmolarities inside and outside the cell

Question 6

If a cell is put in solution with a higher concentration of the permeable solute glycerol:

Answer 6

1. initially the osmolarity is much greater outside the cell and water flows out of the cell
2. at the same time, glycogen is moving down its concentration gradient into the cell
3. eventually, glycogen will build up in the cell and the osmolarity will become greater inside the cell
4. water will then diffuse into the cell causing it to swell

Question 7

In cases where there is a permeating solute, the permeating solute will _______

Answer 7

diffuse across the membrane from higher concentration to lower concentration.

Question 8

If the osmolarity is greater outside the cell, water will flow

Answer 8

out of the cell.

Question 9

If the osmolarity is greater inside the cell, _______

Answer 9

water will flow into the cell.

In either case, water is diffusing in one direction or another in order to dilute solutes and achieve equilibrium.

Question 10

the presence of the nonpermeating molecules inside the cell will reduce the probability

Answer 10

the probability that a water molecule will leave the cell, and this means more water will enter than will leave.

Question 11

This net inward movement of water across a semi-permeable membrane (i.e., a membrane permeable to solvent, but not to solute) is called

Answer 11

osmosis.

Question 12

Cell volume depends only on

Answer 12

the movement of water

Question 13

real cells can’t swell beyond about ____% of their resting volume

Answer 13

140

Question 14

The exact time course of volume change will depend on how

Answer 14

how easily (relative to water) the solute can cross the membrane.

Question 15

Another consequence of a permeating solute is that ____________.

Answer 15

it will not exert as large an osmotic force as a nonpermeating solute at the same concentration

Question 16

The Van’t Hoff equation, relates _______

Answer 16

osmotic pressure to hydrostatic pressure,

Question 17

Diffusion refers to

Answer 17

the random thermally-agitated movement of molecules from regions of higher concentration to regions of lower concentration.

Question 18

Osmosis refers to

Answer 18

the diffusion of water.

Question 19

osmolarity

Answer 19

osM
osmoses of solute per liter
an osmole is the number of osmotically active particles
this is the number of ions/particles present when a compound is dissolved in water

Question 20

Molar equivalents (mEq)

Answer 20

amount of substrate needed to react with or supply one mole of hydrogen ions in an acid base reaction
refer individuals ion concentration

Question 21

tonicity

Answer 21

measure the osmotic pressure between two solutions separated by a membrane and determine whether a cell will shrink or swell

Question 22

hypotonic solution makes cell

Answer 22

swell

Question 23

hypertonic solution makes a cell

Answer 23

shrink

Question 24

isotonic solution results in

Answer 24

no change in cell volume

Question 25

Osmosis occurs at a _______ than simple diffusion because ________

Answer 25

faster rate

of the effect of nonpermeable solutes.

Question 26

water movement into the cell causes

Answer 26

the cell to swell, and unless some countering force is applied, the plasma membrane will be stretched and eventually will rupture.

Question 27

How much the osmotic pressure is diminished depends on________

Answer 27

how easily the molecule can cross the membrane, relative to water.

Question 28

When only nonpermeable solutes are present the osmotic pressure in a system is described by the following equation:

Answer 28

π =RT∆C

Question 29

However, when the solute present is permeant to the membrane, the _______ is diminished. The degree to which the osmotic pressure is diminished depends on ______.

Answer 29

osmotic pressure

how permeable the membrane is to the solute relative to water

Question 30

The equation for osmotic pressure is modified to reflect this effect:

Answer 30

π =oRT∆C

Where o is the reflection coefficient, ranging from 0 to 1. Where 0 is used for a solute that is as permeant as water and 1 is for a solute that is completely nonpermeant.

Question 31

A molecule that crosses half as easily as water will exert _______

Answer 31

half of the ideal osmotic pressure of a non-permeating solute.