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Cells and pH

How do cells deal with changes in pH in their environment?

Many of the biochemical reactions that occur within cells produce end products that affect the pH of the cell.  Every cell has an optimum pH at which the cell will best function.  If the pH of the cell environment varies from the optimal pH too much, the cell could die.  It is vital that cells be able to manipulate their environment to maintain a pH of optimal functioning.  To accomplish this, cells produce buffers.  Buffers are substances that are either weak acids or weak bases that are produced in response to the cell becoming too acidic or too basic.

This concept is very easy to demonstrate to students.  To test this concept, I have the students first take a quantity of water and add drops of HCl acid, drop by drop, recording the pH after every drop.  They repeat using a new sample of water to which drops of NaOH are added.  This serves as a control, showing what happens to the pH when no buffers are being produced.

Next, the students test animal cells and plant cells to see if they can control the pH of their cell environment.  To a given quantity of liver homogenate (liver ground in the blender), students add the drops of acid and base and record the pH.  It is immediately obvious to the students that the cells are producing buffers to control their pH.  Repeating the process with raw potato proves that plant cells also produce buffers.

This is one of my favorite labs that I do with my Biology students.  It clearly shows the concept of buffers, it requires the students to use good lab techniques, the students must table large amounts of data, and the data must be graphed.  Much is accomplished by this lab!

If you are interested, here is a link to the lab I use:

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