BISC 101 Lab Exam 2 QUESTIONS WITH
COMPLETE SOLUTIONS.
What is tonicity? Define the three possible types of tonicity.
Tonicity: the capability of a solution to modify the volume of cells by altering their water content
1. Hypotonic
A solution will be hypotonic to a cell if its solute concentration is lower than that inside the cell
2. Hypertonic
A solution will be hypertonic to a cell if its solute concentration is higher than that inside the cell
3. Isotonic
A solution will be isotonic to a cell if its solute concentration is the same as inside the cell
If a cell is placed into hypertonic solution, the net diffusion of water will go where?
The net diffusion of water will be out of the cell
If a cell is placed into hypotonic solution, the net diffusion of water will go where?
The net diffusion of water will be into the cell
If a cell is placed into isotonic solution, the net diffusion of water will go where?
,There will be no net diffusion of water
What is the difference between diffusion and osmosis?
Diffusion is the movement of solutes and solvents to achieve equilibrium throughout the solution
Osmosis is the movement of only solvents (water) over a semipermeable membrane to achieve
equilibrium (membrane impermeable to solutes)
You place a cell in a solution that is very slightly hypertonic. The membrane is
impermeable to all solutes present. You wait a few minutes. After this time, how might you
describe the tonicity? Explain your reasoning.
Because the membrane is impermeable to all solutes, only water will be able to move via
osmosis
Therefore, water will flow out of the cell from an area of lower solute concentration to an area of
higher solute concentration to achieve equilibrium
Consider a hypothetical and fictional solute, Barkamide. The RBC is somewhat permeable
to Barkamide, and the RBC cytoplasm doesn’t normally contain any Barkamide. The RBC
cytoplasm has a total solute concentration of 0.3M. If you place a cell in a 0.3M solution of
Barkmide, what happens?
Solute Movement:
There is a relatively higher concentration of Barkamide outside than Barkamide inside the cell,
but the total solution is initially isotonic (0.3 M inside and outside the cell)
,Because there is more barkamide outside the cell relative to the inside, barkamide will diffuse
into the cell
Water Movement:
Now that barkamide has moved into the cell, there is a higher solute concentration inside the cell
relative to the outside
Water will then diffuse from outside the cell (lower solute concentration) to inside the cell
(higher solute concentration)
Therefore, the influx of water causes the cell to swell, then lyse
Consider a hypothetical and fictional solute, Wrinklamide. The cell is very permeable to
this solute, much more so than another fictional solute, Barkamide. The normal RBC
cytoplasm doesn’t contain any Wrinklamide or Barkamide.
Make a prediction, and give your reasoning. Which would make the cell lyse faster: 0.3M
Barkamide or 0.3M Wrinklamide?
There is no wrinklamide or barkamide in the RBC, so they will both diffuse into the cell.
Because the cell is much more permeable to wrinklamide than barkamide, there should be faster
net diffusion of wrinklamide. Water will then follow wrinklamide at a faster rate, and cause the
cell to lyse faster
Experiment
, We will place RBCs in various solutes (always at 0.3M), and measure the lysis time. This
will allow us to determine whether red blood cells (RBCs) are permeable to the solute, and
if so, to what extent.
Hypothesis:
Solutes that are more nonpolar will cause a faster lysis time, because the membrane is more
permeable to them.
What is the independent variable in this experiment?
What is the dependent variable?
Why is it important that the concentration of each solute be standardized to 0.3M?
Independent Variable:
The solute (because they have different polarities)
Dependent Variable:
Lysis Time
Why is it important that the concentration of each solute be standardized to 0.3M?
If each solute is not standardized to 0.3 M, it will be a confounding variable. If they are not
standardized, both the polarity and concentration of the solutes will be affecting the lysis time,
and we will not be able to conclude anything about the relationship between (only) polarity and
lysis time
Predict which experimental group should have the fastest lysis time. Explain.
(Note: None of these are initially present inside the cell)
COMPLETE SOLUTIONS.
What is tonicity? Define the three possible types of tonicity.
Tonicity: the capability of a solution to modify the volume of cells by altering their water content
1. Hypotonic
A solution will be hypotonic to a cell if its solute concentration is lower than that inside the cell
2. Hypertonic
A solution will be hypertonic to a cell if its solute concentration is higher than that inside the cell
3. Isotonic
A solution will be isotonic to a cell if its solute concentration is the same as inside the cell
If a cell is placed into hypertonic solution, the net diffusion of water will go where?
The net diffusion of water will be out of the cell
If a cell is placed into hypotonic solution, the net diffusion of water will go where?
The net diffusion of water will be into the cell
If a cell is placed into isotonic solution, the net diffusion of water will go where?
,There will be no net diffusion of water
What is the difference between diffusion and osmosis?
Diffusion is the movement of solutes and solvents to achieve equilibrium throughout the solution
Osmosis is the movement of only solvents (water) over a semipermeable membrane to achieve
equilibrium (membrane impermeable to solutes)
You place a cell in a solution that is very slightly hypertonic. The membrane is
impermeable to all solutes present. You wait a few minutes. After this time, how might you
describe the tonicity? Explain your reasoning.
Because the membrane is impermeable to all solutes, only water will be able to move via
osmosis
Therefore, water will flow out of the cell from an area of lower solute concentration to an area of
higher solute concentration to achieve equilibrium
Consider a hypothetical and fictional solute, Barkamide. The RBC is somewhat permeable
to Barkamide, and the RBC cytoplasm doesn’t normally contain any Barkamide. The RBC
cytoplasm has a total solute concentration of 0.3M. If you place a cell in a 0.3M solution of
Barkmide, what happens?
Solute Movement:
There is a relatively higher concentration of Barkamide outside than Barkamide inside the cell,
but the total solution is initially isotonic (0.3 M inside and outside the cell)
,Because there is more barkamide outside the cell relative to the inside, barkamide will diffuse
into the cell
Water Movement:
Now that barkamide has moved into the cell, there is a higher solute concentration inside the cell
relative to the outside
Water will then diffuse from outside the cell (lower solute concentration) to inside the cell
(higher solute concentration)
Therefore, the influx of water causes the cell to swell, then lyse
Consider a hypothetical and fictional solute, Wrinklamide. The cell is very permeable to
this solute, much more so than another fictional solute, Barkamide. The normal RBC
cytoplasm doesn’t contain any Wrinklamide or Barkamide.
Make a prediction, and give your reasoning. Which would make the cell lyse faster: 0.3M
Barkamide or 0.3M Wrinklamide?
There is no wrinklamide or barkamide in the RBC, so they will both diffuse into the cell.
Because the cell is much more permeable to wrinklamide than barkamide, there should be faster
net diffusion of wrinklamide. Water will then follow wrinklamide at a faster rate, and cause the
cell to lyse faster
Experiment
, We will place RBCs in various solutes (always at 0.3M), and measure the lysis time. This
will allow us to determine whether red blood cells (RBCs) are permeable to the solute, and
if so, to what extent.
Hypothesis:
Solutes that are more nonpolar will cause a faster lysis time, because the membrane is more
permeable to them.
What is the independent variable in this experiment?
What is the dependent variable?
Why is it important that the concentration of each solute be standardized to 0.3M?
Independent Variable:
The solute (because they have different polarities)
Dependent Variable:
Lysis Time
Why is it important that the concentration of each solute be standardized to 0.3M?
If each solute is not standardized to 0.3 M, it will be a confounding variable. If they are not
standardized, both the polarity and concentration of the solutes will be affecting the lysis time,
and we will not be able to conclude anything about the relationship between (only) polarity and
lysis time
Predict which experimental group should have the fastest lysis time. Explain.
(Note: None of these are initially present inside the cell)
