Mr. Potato Head meets Bugs “What’s Up Doc?” Bunny

(rubric)

 

Read the introduction: This investigation will explore the movement of water from an area of high concentration of water molecules to an area of low concentration of water molecules. This is also called water potential. Using water potential as a description of potential energy, water molecules will flow from a higher concentration of water molecules to a lower concentration of water molecules through a selectively permeable membrane.

There is another way to view this phenomenon; where there is a large amount of solute there is a corresponding lower amount of water. This solution is called a hypertonic solution in relationship to the cell.  The reverse of this situation is called a hypotonic solution in relationship to the cell.  When solutions on opposite sides of a selectively permeable membrane have an equal proportion of solute to water, the solutions are said to be equal, or isotonic to each other and are in a state called dynamic equilibrium.

In this activity you will be given the opportunity to investigate this movement of water, which is a special case of diffusion called osmosis.

Problem: How do the isotonic nature of a potato and carrot compare?  (I.O.W.: Which has more water...a potato or a carrot?)

Pre-lab:

  1. Read the entire lab exercise.

  2. Make a hypothesis  (If, then) that answers the problem. 

  3. List the IV, DV, and 5 SV for this activity.

  4. Make a data table. There are always many questions about this....think about what you are doing and what you are measuring.  You should have a place on your data table to write all of that information.

Procedure (for a group of 4 students):

First Day:

  1. Obtain three small  beakers and three slices of carrot or potato (peeled and 4-5 mm thick).

  2. Using a weighing tray, tare the balance back to 0.00 grams. Then mass the individual slices of the vegetable using a pair of forceps to handle.  Record the mass to the hundredth place in your data table.

  3. Your table will be assigned three different solutions of sucrose* to place your slice in overnight.

  4. Label your beakers with masking tape; write your table number, period number and the percentage of sucrose and the veggie assigned to your table. Place a veggie slice in each beaker, be careful to note which veggie slice is in which beaker. Pour enough of the solution to just cover the veggie slice (approximately 15 ml).

  5. Cover your beakers with plastic wrap over the tops.  Set the beakers aside on your lab table.

*  There are six sucrose solutions, 0%, 4%, 8%, 12%, 16%, and 20%; and, two veggies: carrot and potato. 

Second Day:

  1. Gently remove the veggie slice with forceps, one at a time from each beaker.

  2. Hold the veggie slice at an angle and gently wipe any excess solution from the edge each carrot using the provided paper towels. Don't press too hard or else water inside the veggie can be extracted onto the paper towel.  Don’t mix-up the veggie slices.

  3. Re-mass each veggie (using same balance and technique as on day one).

  4. Record your data in your data table.

  5. Clean up your beakers, forceps and tables (please don’t leave a sticky mess). There is a bucket of soapy water on the front lab bench. Rinse your beakers and forceps and place in the tray on the front lab bench.

  6. Share your table data with your partner table.

  7. Calculate the % change in mass for all carrots. % change = Final mass - Initial mass/ Initial mass X 100