Osmosis/Diffusion Lab                             Hour 1 2 3 4 5                 Name                                              .

INTRODUCTION:
Individual cells exist in a LIQUID environment of about 75% water.  This  environment makes it easier for materials like food, water, and oxygen to move into and out of a cell.  The movement of molecules from an area of HIGH concentration to an area of LOW concentration is known as                                        .

   A. What two factors determine whether diffusion will occur?
         1.                                                                                                                                                        .
         2.                                                                                                                                                         .

   B. The diffusion of water molecules through a selectively permeable membrane =                            .
            What is a selectively permeable membrane?                                                                           .

CONCEPT  Cell membranes are selectively (or semi) permeable to water.

OBJECTIVES  The student will be able to conclude from their own data that cell membranes are selectively permeable and that water moves from areas of high concentration to areas of low concentration within cells.

EQUIPMENT AND MATERIALS
      Plastic cups      potato slices      5% NaCl Solution       Some sort of Soda         Pure Water
      Balance            carrot slices       red onion cells            20% NaCl Solution        Egg & vinegar

PART I,  DAY  1:  In groups of 3-4,

1.  Obtain four cups and label them   5% NaCl,   20% NaCl,   Coke,   Diet Coke, & Pure water.

2.  Select five carrots and five pieces of potato that are approximately the same size.   After first zeroing your balance to make sure it is accurate, weigh each item,  record its mass on the data table in the BEFORE column, and place it in the appropriately labeled cub.

4. Add enough solution to cover the items in each cup.  ALL CUPS SHOULD HAVE = AMOUNTS OF SOLUTION.

5. Write your name on a piece of paper and set your cups on it in the designated area.

6.  The following class period - Check your balance for accuracy.  Starting with one cup at a time, remove each item, pat it dry with a paper towel, and determines its mass.  Record the results on your data table in the column labeled AFTER.   Determine how much the item’s mass changed.

7.  Obtain a red onion cell and the prescribed solutions from your teacher.

8.  Focus on the onion at 40X and draw a picture of the onion cells.  Pay close attention to the cell walls and the red portion of each cell.  The red portion is the vacuole.

9.  Carefully add 1 or 2 drops of  20% NaCl solution to the side of the cover slip. Watch the red onion cells for several minutes until the red portion begins to shrivel up.  Draw a picture of what you see.

10. Remove the slide and with an eyedropper carefully rinse the NaCl solution from the slide.  Refocus on the onion cells and  add 1 to 2 drops of Pure water.  Watch the onion cells until the red portion reappears.   Draw a picture of what you see in the space provided.

QUESTIONS:
1.  What effect did each solution have on the vegetable?  Using your knowledge of osmosis and diffusion explain these results.
 
 
 
 
 
 

2.  Using the concept of osmosis and diffusion, explain why the vacuole (the red part of the onion) shriveled up when you added 20%NaCl.
 
 
 
 

3.  When you are thirsty, is it best to quench your thirst with  pop or water?  Use the results from the lab to explain.