AP Biology- Osmosis Lab
Water can passes through selectively permeable membranes slowly through the membrane by osmosis
or through specialized protein channels called aquapoerins. Aquaporins allow the water to move more
quickly than it would through osmosis. Most other substances such as ions, move through protein
channels, while larger molecules including carbohydrates move through transport proteins. Water moves
through membranes by osmosis. Like solutes, water moves down its concentration gradient from areas of
high water potential and low solute concentration to areas of low water potential and high solute
concentration. Solutes decrease the concentration of free water, since water molecules surround the
solute molecules. Hypertonic, hypotonic and isotonic are used to describe solutions separated by
selectively permeable membranes. Hypertonic solutions have a higher solute concentration and a lower
water potential as compared to the other solution; therefore water will move into the hypertonic solution
through the membrane by osmosis. Hypotonic solutions have a lower solute concentration and a higher
water potential than the solution on the other side of the membrane; water will move down its
concentration gradient into the other solution. Isotonic solutions have equal water potentials.
Directions:
1.) Day 1: Obtain a potato and peel the potato. Cut it up into equal size cubes approximately 1 cm3 .
Make enough to have three potato cores per solution. You will be testing 5 different molarities of
two different solutions. You will need 30 potato cubes.
2.) Obtain 10 cups/beakers. You will use two different solution. Choose from sucrose solution, salt
solution or glucose solution. Label each cup with solution type and your groups name. Fill each cup
with 50 mls of the colored solutions. Your teams solutions are:
Solution A:_____________ Solution B:_____________
3.) Determine the mass of 3 potato cores together and record each set of 3 in the table below under
initial mass. Put the potatoes in the solution filled cups. Let the potatoes sit until we return to class.
4.) Day 2: Remove the potatoes from each of the beakers and carefully blot off any excess solution.
5.) Determine the mass of the 3 potatoes together and record their final mass in the appropriate
column. Calculate the percent change in mass= (final mass-initial mass)/ initial mass. Then multiply
your answer by 100.
6.) Gather the data from the other groups in the class that have the same solution and find the class
average (mean) for each of the colored solutions.
7.) Based on the change in mass, determine the Molarity of each colored solution based on your
potato results. Which solution should cause the greatest gain in mass in the potatoes, which the
least?
8.) Once you determine your results, order the colored solutions from greatest Molarity to least and
record in your data table.
(1.0 M, 0.8 M, 0.6 M, 0.4M, 0.2M and 0 M)
9.) Grab a graduated cylinder and test your results. Try to layer the solutions in a graduated cylinder
with the greatest Molarity (1M) on the bottom to the least Molarity (0M) on the top. If you order
them properly, you should see layering in the cylinder. Hint: slowly pour the solutions into the
cylinder.
Solution A :______________________
Solution Molarity
% Change
Initial Mass Final Mass Mass Difference
A
in Mass
Class Mean
Class SD
Blue
Yellow
Red
Green
Clear
Solution B:_____________________________
Solution Molarity
% Change
Initial Mass Final Mass Mass Difference
A
in Mass
Blue
Yellow
Red
Green
Clear
Class Mean
Class SD
10.) Graph the results for both your individual data and class average on a graph. In order to do so,
the 0 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. The x
axis is the sucrose Molarity within the beaker.
11.) Determine the molar concentration (osmolarity) of the potato cores. This would be the sucrose,
glucose or salt molarity in which the mass of the potato core does not change. To find this, draw
the straight line on your graph that best fits your data. The point at which this line crosses the x
axis represents the molar concentration of sucrose, glucose or salt with a water potential
that is equal to the potato tissue water potential. At this concentration, there is no net gain or
loss of water from the tissue.

Your determination of the molar concentration (osmolarity) of your potato as it relates to your solution.
This is where the mass of the potato cores would not change – use your regression analysis for this
calculation. Use the formula for the straight line that best fits your data. The point at which this line
crosses the X-axis represents the molar concentration of sucrose, glucose or salt with a water potential
equal to the potato tissue water potential—therefore, it will be where there is a 0% change. Be sure to
include this very important calculation y=mx + b
12.) From the graph determine the Molar concentration of the potato? ___________
Solution A:_____________________________
Solution B:_____________________________
Osmosis Lab Part II
Submit your write up to me by Friday via google docs.
Introduction:
Write a brief introduction about osmosis in living cells.
Data
1.) Insert your data into in Excel. Use Molar Concentration and Mean % change. Plot each set of
data using a scatter plot. Then use the chart tools/ layout to insert the trend line (linear
regression line) and the equation of the line. Label the graph and include your axis titles.
2.) Plot both sets of data.
3.) Determine the Molar concentration of the potato for the two solutions.
Post lab Questions:
1.) Based on your data, was the molar concentration of the potato in each solution the same? In
other words at what point does the net movement of water equal zero? Explain.
2.) What factors determine the rate and direction of osmosis?
3.) Based on your data, can you predict the direction of osmosis in living cells when the cells are
placed in various solutions? Explain.
4.) Describe the difference between water potential and solute potential.
Include an error analysis section and a conclusion.