Transport in Plants

• Volume of the solution (30 cm3; I ensured that the potato strips were submerged completely inside the solution)
• Shape of the potato strips (cuboid); As the shape varies, so does the surface area in contact with the solution
• Same type/quality of potato
• Temperature of the solution (more osmotic activity would happen if the temperature is higher)
• Number of potato strips in each solution (3)

APPARATUS AND MATERIALS REQUIRED:

• Cork borers and scalpel/ knives
• 50 cm3 beakers
• 25 cm3 measuring cylinders (± 0.05 cm3)
• Electronic weighing balance (to measure the mass of potato strips) (±0.01 g)
• Permanent marker (to label the beakers so as to remember which beaker contains which sugar concentration)

• A raw potato
• Glucose solution of concentrations 0.1 M, 0.2 M, 0.3 M, 0.4 M, 0.5 M
• Distilled water (0.0 M)
• Tissue paper

STEP BY STEP PROCEDURE:

1. Collect fresh raw potatoes and remove their skin
2. Using knives and cork borers, make strips of the potatoes
3. Pour 25 cm3 solutions of different molar concentration of glucose: 0.0 M (distilled water), 0.1 M, 0.2 M, 0.3 M, 0.4 M and 0.5 M in six separate beakers respectively. Remember to label each beaker with a permanent marker the concentration of sugar solution that beaker contains.
4. Weigh the potato strips using a weighing balance before the experiment. To obtain more accurate and reliable results, it is suggested to place three potato strips in each beaker and hence, take three readings
5. Record the mass of each potato strip in a table, and make note of any qualitative observation
6. After about 24 hours, observe the condition of the chips. Record all the physical changes
7. Measure the mass of the potato strips in each beaker after the experiment. While doing so, remove excess surface liquid by using some tissue paper.
8. Enter the readings in a table. The isotonic point is the point when there is no change in the mass of the potato strips. The isotonic point, therefore, is the point where the graph (sugar solution concentration v/s change in mass) intersects the x-axis.

OBSERVATION:

RAW DATA TABLES

PROCESSED DATA TABLES:

• To find the change in mass, I subtracted the mass of the potato strip before from the mass of the potato strip after. This is expressed as: CHANGE IN MASS = MASS AFTER – MASS BEFORE
• To find the average, I added the mass difference calculated for each of the three strips (before and after), and divided this sum by 3. Therefore AVERAGE = (1 MASS + 2 MASS + 3 MASS) ÷ 3

        

• To find the % change in mass, I divided the difference in mass by the original mass and multiplied this quotient by hundred. This can be expressed as: % change in mass = (change in mass * 100) ÷ initial mass 
• To find the average, I added the mass % difference calculated for each of the three strips (before and after), and divided this sum by 3. Therefore AVERAGE = (1 MASS % + 2 MASS % + 3 MASS %) ÷ 3
• To find the average for the 0.3 concentration % mass change, the anomaly 8.13 was ignored. Therefore, only 2.73 and -5.88 were added (and the sum was divided by 2) in order to calculate the mean percentage change.

CONCLUSION:

Table 3 and Table 4 suggest that as the concentration of sugar solution increases, the change in mass of the potato cells decreases.                                                                                                                  This is because the water potential of the solution would be lower than that of the potato cells, and we know that the transport of water through osmosis occurs from a region of high water potential to a region of low water potential. This implies that water molecules would flow out of the potato cells and they would lose mass, causing the stripes to shrink and the cells to become flaccid.                                                                                                                         In biological terms, this process is more specifically known as exosmosis, and occurs in hypertonic solutions. A hypertonic solution is one where the concentration of water molecules is more in the solute than in the solvent.

This theory explains why the mass of the potato strips increased when left in low concentration of sugar solution (0.0 M, 0.1 M, 0.2 M and 0.3 M). As the water potential of the solutions was higher, water was transported into the potato cells, causing the potato strips to bloat and the cells to become turgid.                                                                                                                 In biological terms, this process is more specifically known as endosmosis, and occurs in hypotonic solutions. A hypotonic solution is one where the concentration of water molecules is less in the solute than in the solvent.

My hypothesis is proven correct.

EVALUATION:

Factors that could have caused inaccuracy:

• While labeling the potato strips, I used a gel pen once for the third strip in the 0.3 M sugar solution. A small amount of ink might have diffused from the potato strip into the solution, which was why I obtained an anomaly in that case.
• All the potato strips were handled with bare hands, which implies that impurities from the hands mixed with these strips. This must have affected the osmotic activity between the potato and the solution.
• The beakers were left uncovered, meaning that:

1. Any impurity from the surroundings could have mixed with the solution- again affecting the osmotic activity between the potato cells and the sugar solution.
2. A small portion of the solution might have evaporated, leaving the upper surface of the potato strips unexposed to the solution