Name___________________ Block_____________
Osmosis, water potential, graphing and more!
Mrs. Jarvis made six different solutions, each containing various concentrations of
sucrose, but she forgot to label each one! It is your group’s task to solve the mystery of
which solution represents each of the possible molar concentrations: 0.0 M sucrose, 0.2
M sucrose, 0.4 M sucrose, 0.6 M sucrose, 0.8 M sucrose, and 1.0 M sucrose by
measuring the change in the mass of carrots and potato samples.
Statistics Background:
● Standard Deviation measures how spread out the data is from the mean.
o A lower standard deviation means that the data is closer to the mean, and
that there is a greater likelihood that the independent variable is causing
the changes in the dependent variable.
o A higher standard deviation means that the data is more spread out from
the mean, and most likely other factors other than the independent
variable are influencing the dependent variable.
● Standard Error indicates how well the mean of a sample estimates the true
mean of a population.
Background information
Water moves through membranes by diffusion; this process is called osmosis. Like
solutes, water moves down its concentration gradient. Water moves from areas of high
water potential (high water concentration) and low solute concentration to areas of low
water potential (low water concentration) and high solute concentration. In plants with
a cell wall, osmosis is affected not only by the solute concentration but also by the
resistance to water movement in the cell by the cell wall. This resistance is called turgor
pressure (the physical pressure exerted on the cell).
Hypothesis:
If the potato decreases in mass, then it is in a ________________________
solution, because…
____________________________________________________________
____________________________________________________________
If the carrot increases in mass, then it is in a _________________________
solution, because…
____________________________________________________________
____________________________________________________________
Materials:
6 Potato chunks, 6 carrots
Balance
6 sucrose solutions ( 0M, 0.2M, 0.4M, 0.6M,
0.8M & 1.0 M)
Plastic cups
Paper towels
Procedures:
Day 1:
1. Label your cups by lab group number.
2. Obtain 6 equally sized pieces of carrot and potato. Blot each sample.
Determine the mass of each and record the initial mass in the table 1 (one
decimal place) Be careful not to mix them up. Mass one vegetable at a time
and place it directly into the appropriate cup.
3. Pour enough colored solution over each vegetable to cover the vegetables
completely. Cover each cup with a lid.
4. Place all cups in appropriate blue tray.
Day 2:
1. Remove the vegetables from each cup ONE AT A TIME and blot dry!! Be
careful not to mix them up. Measure the mass one at a time then return it to
the appropriate cup.
2. Determine the final mass and record in Data Table.
3. Calculate the percent change using the % change equation below.
% change =
Final Mass - Initial Mass
Initial Mass
X 100
Table 1
Solution
Vegetable
Initial mass
Final mass
% change*
color
type
Red
Red
Yellow
Yellow
Green
Green
Blue
Blue
Purple
Purple
Clear
Clear
MOLAR CONCENTRATION DATA-Based on what you know about osmosis, water
potential, and the data above what are the molar concentrations of the colored mystery
solutions. Record in Table 2
Table 2
SUCROSE
COLOR
0 M sucrose
0.2 M sucrose
0.4 M sucrose
0.6 M sucrose
0.8 M sucrose
1.0 M sucrose
Teacher initials______
After you have had me check your above work, record your % change for
each sucrose concentration on the white board in the appropriate group
number.
Class data:
Table 3
Potato % change for each group
1
2
3
4
5
6
7
8
9
10
11
12
Mean
SD
SEM
8
9
10
11
12
Mean
SD
SEM
0M
0.2 M
0.4 M
0.6 M
0.8 M
1.0 M
Table 4
Carrot % change for each group
1
2
3
4
5
6
7
0M
0.2 M
0.4 M
0.6 M
0.8 M
1.0 M
Graph: Change in mass of potato and carrot is due to water gain/loss as a function of
sucrose concentration.
Independent variable__________________
Dependent variable___________________
1. Do not graph your groups’ data. On a piece of graph paper, graph the results
for the CLASS AVERAGE ONLY for carrot and potato. In order to do so,
the zero axis line should actually be in the middle of your graph. The y axis above
this line should be labeled % increase in mass while the y axis below this line
should be labeled % decrease in mass. The x axis is the solute concentration
(molar) within the beaker.
2. When completed, use a ruler to draw a straight line of best fit through your six
data points. Each plant should have separate color.
3. Where the line of best fit crosses the horizontal zero line, draw a vertical line
down to the x-axis. This is the point at which the plant tissue is isotonic with its
surroundings, and is therefore the estimated sucrose concentration of the plant.
What is the sucrose molar concentration of the potato?___________
What is the sucrose molar concentration of the carrot?___________
4. Water potential for the potato and sucrose solution-watch power point. Number
3 gives you C for the following equation:
Figure out the water potential for the sucrose solution using the following equation. Use
your molar concentration for the potato:
𝜓s = -iCRT
i=ionization constant-for sucrose this is 1 because it does not ionize in water
C=molar concentration you figured out in number 3 for potato
R= pressure constant .0831 liter bar/mole K
T=Temperature (degrees C + 273)
Show calculations below for 𝜓s
Now calculate water potential for the sucrose solution where 𝜓=𝜓s +𝜓P
𝜓P =0
Questions:
1. Which solution served as the control for this experiment & why?
2. Why did some potato samples gain water and others lose water? Was there any
pattern?
3. What happens when a thirsty person drinks something sweet to try to quench
their thirst?
4. When a cell gains water, what happens to its size and mass?
5. When a cell loses water, what happens to its size and mass?