Aim: to Determine the Biological Changes to Potato Cores Over a Period of Time When They

The Spineless Potato 1

Aim: To determine the biological changes to potato cores over a period of time when they are exposed to different solutions and to relate these changes to osmosis. Materials  6 potato cores,  A beaker of; (label each beaker as you prepare it) o 100 ml distilled water water o 1 sugar cube in 100 ml o 3 sugar cubes in 100 ml water water o 2 sugar cubes in 100 ml o 4 sugar cubes in 100 ml water  a graduated cylinder (10 – 20  a ruler ml)  a balance (at front of lab)  a scalpel  6 petri dish covers  a dissecting needle  1 ziploc bag

Overview; By placing pieces of a potato into solutions with different concentrations of solute (sucrose), water may flow into or out of the potato. Knowing whether or not water flowed into or out of the potato will give you an idea of approximately what percentage of a potato is water. Method 1. Using the potato corer, carefully cut six cores out of your potato. Using the scalpel carefully cut each potato core into a cylinder of about three to five centimeters in length. Make sure that all of the potato cores are the same length. Record the length in a table. Record the diameter of each potato core. 2. Using the balance, measure and record the mass of each potato core. 3. Fill the graduated cylinder with tap water two-thirds of the way up. Measure and record the volume of water in the graduated cylinder. Attach each potato core, one at a time, to the end of the dissecting needle and hold it so that the potato core is completely submerged in the water. Measure and record the water level in the cylinder. The difference in your two measurements is the volume of the potato core.

4. Place one potato core in each of your labeled beakers and one into the Ziploc bag.

5. Cover the top of each beaker with a petri dish cover. 6. Place your beakers on the side counter, on top of a piece of paper towel you’re your lab groups names. Allow the beakers to sit overnight.

7. Remove the cores from each beaker. With a piece of paper towel carefully blot the excess moisture off each potato core. Measure and record the length, diameter, mass, and volume of each potato core, as you did previously. The Spineless Potato 2

Results Record the data you gathered on the first and second day in the table below. Physical changes in the potato cores

Treatment Length Diameter Mass Volume Turgidity (Controlled variable) Day Day Day Day Day Day Day Day Day Day 1 2 1 2 1 2 1 2 1 2 1 sugar cube

2 sugar cubes

3 sugar cubes

4 sugar cubes

Distilled water

Ziploc bag

Record any qualitative changes (in color, texture, etc.) you noticed in the potato cores.

Definitions of terms In answering the questions and writing your conclusions, you should use the following terms to make your answer complete.  Diffusion - the movement of molecules from an area of high concentration to an area of low concentration  Osmosis - the diffusion of water  Plasmolysis - a type of osmosis in which water moves out of the material  Deplasmolysis - a type of osmosis in which water moves into the material The Spineless Potato 3

 Isotonic solution - a solution with equal concentration of solute inside and outside of the material  Hypertonic solution - a solution with more solute in the surrounding environment than in the material  Hypotonic solution - a solution with less solute in the surrounding environment than in the material (Remember that water concentration is the opposite of the solute concentration – in hypertonic solutions, the concentration of water molecules is lower outside the cell and in hypotonic solutions the concentration of water molecules is higher outside the cell.) Water always moves from anarea of high concentration to low concentration.

 Turgor pressure helps give plants structure and strength. It is the force that the contents of a plant cell exert on the cell wall and is the result of the osmotic entry of water into the cell, The flexibility of the potato can be used to determine turgor pressure. (turgidity) The more flexible the potato stick, the less the turgor pressure.

Lab Report This will be a formal lab report – use formal lab format given. You will need to include a graph of your results. The discussion part of the report will be to answer the questions below.

Questions 1. In this experiment, why was it important that the potato cores were the same length? 2. Why was it important to cover each beaker with a piece of aluminum foil? 3. Into which of the potato cores did water flow? From which of the potato cores did water flow out? How can you tell? 4. Which solution causes the greatest change? (Mass, length, diameter, volume and turgidity) 5. Which solutions (if any) were hypertonic, isotonic, or hypotonic? Explain how you know. Make a sketch of the potato sticks and use arrows to show the direction of water movement across the potato cell membranes in each type of solution. 6. Which solutions caused the turgidity of the potato to change? Explain why you think this happened. 7. What was the control for this experiment? Why? 8. Which type of solution do you think would be most beneficial to the plant? Why? The Spineless Potato 4

Sources of Error Identify any possible sources of error that may have affected the results of this experiment.