ACTIVE TRANSPORT ACROSS THE PLASMA MEMBRANE

Dorothy Sarmiento              Lindbloom Technical High School
                               6130 S. Wolcott Ave.
                               Chicago, IL 60636
                               1-312-471-8721

Objective:
The student will be able to comprehend that energy is required to move 
substances across the cell membrane against the concentration gradient.

Materials:
Dry Yeast
0.75% Na2CO3
0.02% neutral red dye
0.75% acetic acid
filter paper discs to fit funnels

Strategies:
Demonstrate the dye (neutral red) by adding weak acetic acid. Color change 
occurs.
Place 25 ml of 0.75% Na2CO3 in a large test tube. Add 1 gm dry yeast.  
Boil solution gently for 2 minutes.  Label the tube A.
Place 25 ml of 0.75% Na2CO3 in a large test tube, warm, and then add 1 gm 
dry yeast.  Allow the solution to sit for 10 minutes( to activate the 
yeast)  Label the test tube B.
Add 25 ml of 0.02% neutral red to test tube A.  Observe and record color 
change.
Add 25 ml of 0.02% of neutral red to test tube B. Observe and record color 
change.
Filter a portion of the contents of each test tube.  Observe and record 
color of cells left on the filter paper and color of solution of each test 
tube.
Think about your observations and answer the following questions:
a) Did the dye enter the cells of either test tube?
b) Did Na2CO3 enter the cells of either test tube?
c) Is the cell membrane of the cells of A or B permeable?
Conclusion? Either the cells of test tube B put out something to change the 
solution or the dye entered the cells and was changed in the cytoplasm. (It 
is known that the cytoplasm is slightly acidic)
  
Add an equal amount of acetic acid to the remaining contents of test tube 
A.
Observe and record any color change.
Filter a portion of the suspension.  Record color of cells.
Remove the filter paper of the original filtration of test tube A contents.
Place a drop of acetic acid on the cells.
Observe and record any color change.