Acids, Bases, Cells and Buffers Lab
Anatomy & Physiology
NAME____________________________________ PER _____
Enzymes are essential to chemical reactions in cells, but they are also sensitive to environmental factors such as heat.
The pH (how acidic or basic something is) of tissues can affect enzyme activity as well. Remember from chemistry, a pH
of 7 is neutral, 1-6 is acidic, and 8-14 is basic (sometimes called alkaline). Most cells maintain a pH close to neutral.
Biochemical activities of living tissues frequently tend to change pH. Yet life depends upon maintaining a pH that will not
inactivate the enzymes working in that tissue. So how do living tissues maintain a certain pH under changing conditions?
Problem: Which material acts most like a buffer? Answer the question for your hypothesis.
Materials: pH paper, 0.1M HCl, 0.1M NaOH, commercial buffer solution, liver and potato homogenates (10g per 100mL
of water), 50mL beaker.
Procedure: Part A – Tap Water
1. Pour 25mL of tap water into a 50mL beaker. Record its initial pH. The pH paper is expensive, and should be
used in small pieces. Discard your paper in the trash as you use it.
2. Add 0.1M HCl a drop at a time and record the pH after every two drops have been added until you get to 10
drops. Then, record the pH after every 5 drops until you have added a total of 30 drops. Prepare a data table
and be sure to record your results as you go.
3. Rinse the beaker and pour into it another 25mL of tap water. Record the initial pH and add 0.1M NaOH drop by
drop, recording the pH in exactly the same way as for the 0.1M HCl. After 10 drops, proceed with 5 drops at a
time until 30 drops have been added (a total of 30 drops).
Procedure: Part B – Animal Tissue (Liver Homogenate)
1. Now try living tissue. Rinse your beaker and pour 25mL of liver homogenate into it. Record the initial pH. Add
0.1M HCl one drop at a time and record the pH for every 2 drops up to the first 10 drops. Thereafter, record the
pH after every 5 drops until 30 drops have been added. NOTE: You must stir after adding drops and before
measuring pH to get an accurate reading.
2. Rinse the beaker. Measure out another 25mL of liver homogenate. Repeat the procedure above, except use
0.1M NaOH instead of the acid.
Procedure: Part C – Plant Tissue (Potato Homogenate)
1. Try plant tissue – potato homogenate – to see if plant tissues react the same way as animal tissues. Rinse your
beaker and pour 25mL of potato homogenate into it. Record the initial pH. Add drops of HCl as you did before
until 30 drops have been reached.
2. Rinse your beaker. Repeat the whole procedure using the NaOH instead of the acid.
Procedure: Part D – Commercial Buffer
1. Chemists can purchase buffers to control pH during certain lab tests. Rinse your beaker and add 25mL of the
commercial buffer. Test this with the HCl as you did the water, liver and potato.
2. Rinse your beaker. Repeat the procedure using NaOH.
Data: Make a table for each procedure above that shows the pH values at each interval of drops for both HCl and NaOH.
Observations/Analysis:
1. Make a large, full-page line graph, plotting two lines for the change of pH in tap water (y-axis) against the number
of drops of acid and base solutions added (x-axis). Use the same color pencil for these two lines. At the ends of
the lines write “TAP WATER”. Be sure to allow spaces on the bottom for the jump from 2 drops to 5 drops.
2. Graph and label the results for “LIVER” on the same line graph, using a different colored pencil.
3. Graph and label the data for the “POTATO” and “COMMERCIAL BUFFER” on the same graph in different colors.
4. Summarize the effects of HCl and NaOH on tap water. Does there seem to be a steady increase, or a sudden
jump? Is there any correlation between the number of drops and the change in pH?
5. What was the total pH change for the 30 drops of acid added to the liver?
6. What was the total pH change for the 30 drops of base added to the liver?
7. How do these differ from the tap water?
8. How do you account for the difference in the liver and tap water?
9. Is the action of the commercial buffer solution more like the tap water or the liver and potato?
10. Do you think living cells have built in buffers?
11. What do you think would be the advantage of having organic buffers in cells?