Names: Delete Red Instructions like “Insert Name Here”
Due: MON Nov 23rd
Points:
/ 30
DIALYSIS LAB
Background
Water molecules are made of two hydrogen atoms and one oxygen atom (3 total). Glucose molecules are
made of six carbon atoms, twelve hydrogen atoms, and six oxygen atoms (24 total). When glucose
molecules join together, they form long chains of complex sugars – called starches (hundreds total).
Glucose and starch can form solutions when dissolved in water. Benedict’s Solution is a glucose indicator
with a progressively blue positive reading. Iodine can be used as a starch indicator with a dark black/brown
positive reading.
Water
Glucose
Starch (glucose chains)
Healthy kidneys clean your blood by removing excess fluid, minerals, and wastes. Patients with kidney
failure are sometimes unable to keep up with the daily filtering needs. In these cases, patients may need
to use dialysis machines to help filter their blood. Blood is pumped through a filtering system across the
dialysis tubing membrane, and the cleaned blood is returned to the body. Dialysis tubing, in many ways,
acts like the plasma membrane of a cell.
Purpose
To determine factors that affect the rate of diffusion across dialysis tubing
Materials
 Dialysis tubing
 String
 Distilled Water
 Starch




Glucose
Benedict’s sol.
Iodine
Beakers




Independent Variable:
Dependent Variable: rate of diffusion
Control Variables:
Hypothesis: How will your independent variable affect your dependent variable?
Heating Plates
Timers
Drying towels
Scales
Procedures
 Create an experiment that measures a factor of the rate of diffusion.
 Perform at least three iterations of the independent variable
 Measure the rate of diffusion by massing a “cell” every five minutes for at least 30 minutes
Cell 1
Cell 2
Cell 3
Cell Solution
Beaker Solution
Data

Create a data table you will use to record the cell masses
- Create the table in Excel to make data analysis easier
Analysis
 Create a graph that shows the calculated diffusion rate of all three cells
 Answer analysis questions
1. Which cell-beaker trial experienced the most diffusion? Why?
2. Which cell-beaker trial experienced the least diffusion? Why?
3. How would your results have changed if you used a different solute (i.e. dextrose instead of
starch, or starch instead of dextrose)?
Conclusion
1. What are potential sources of error in the experiment? What can be done to reduce these
errors?
2. What future experiments could be done to elaborate on the experiment? Complete an
experimental set-up below (alter if needed) to show what would be tested.
Cell 1
Cell 2
Cell 3
Cell Solution
Beaker Solution
3. In a simplified dialysis machine, human blood is
flowed next to the dialysis solution called
dialysate. The semi-permeable membrane
between the two fluids creates a concentration
gradient. The purpose of dialysis machines is to
get rid of urea and other wastes. Let’s assume
that we want to keep the Na+ and K+ salts in the
blood. Given the concentration of blood, what
should be the concentration of solutes in the
dialysate in order to maximize the removal of urea
waste while maintaining salt levels in the blood.
Blood
Dialysate
% Na+
5
?
% K+
5
?
Explain the reasoning for the solute concentrations.
% Urea
10
?
% Water
50
?