It was concluded from the pilot study what when the experiment took place, the potato chips would be placed in 0% sodium chloride solutions as the potato chips placed in the distilled water gained more mass that the potato chips in the 10% sodium chloride solution via osmosis. The more mass gained, the more accurate the measurements will be as the difference in mass will be more easily distinguishable and therefore easier to read.
Method:
- Set up the equipment as shown in the diagram.
- Cut 14 potato chips. Weigh and record the mass of each chip.
- Measure 30ml of distilled water (0% sodium chloride solution) using the measuring cylinder and the pipette and pour into a boiling tube. Do the same for another boiling tube.
- Place two potato chips in the 2 boiling tubes of distilled water and at the same time start the stop clock. Leave the potato chips in the 0% Sodium Chloride solution for five minutes.
Repeat the above seven times. Each time leave the potato chips in the distilled water for firstly 5 minutes, then 10 minutes, 15 minutes, 30 minutes, 40 minutes, 50 minutes and finally 60 minutes.
Two potato chips are placed in the 0% sodium chloride solution for one measurement to make sure the results recorded are reliable.
For accuracy the potato chips must be put in and taken out of the 0% sodium chloride solution at the exact time specified. When the potato chips are removed from the potato, take the excess liquid off the chip using tissue. The tissues must be sterile as a small amount of osmosis may occur if the tissue is contaminated with a higher percentage of sodium chloride solution. The weighing scales the potato chips are weighed on must be dry and have no original weight of any other substance (for example excess water if the chip has not been adequately dried.) before the potato chips are weighed.
The experiment has been planned so that seven measurements are made to ensure clear results, and to prevent anomalies from have a serious affect of the analysis of the results recorded.
Controlling Variables:
Throughout the experiment, the following variables must remain constant, as a change in more than one variable would render the experiment an unfair test:
- The temperature of the room in which experiment is to be conducted is to remain constant. This may be controlled by the use of central heating and a thermostat.
- The concentration of the sodium chloride solution must remain the same; therefore the 0% sodium chloride solution must be uncontaminated for a fair test.
- The vegetable used in the experiment must remain the same; no variations in the type of potato may be used.
- The volume of the solution the potato chips are placed in must remain the same throughout the experiment. The potato chips must be placed in exactly 30ml of 0% sodium chloride solution.
Prediction:
I predict that then mass of the potato
Chip will increase as the length of
Time increases. This prediction of
The results graph shows the cells of the potato chip gaining water inside the cells. The line has flattened off because the cells of the potato cannot hold any more water.
Scientific explanation:
Osmosis is the movement of water molecules across a selectively permeable membrane from a region of high water potential to a region of low water potential.
When osmosis occurs in a plant cell and the plant cell has lower water potential, the cell swells, and become turgid. The cell wall of the plant prevents cells from bursting due to high net flow of water into the cell.
As the plant cells gain water potential by osmosis the mass of the plant increases as the water in the cells increases.
As the plant cell is left in the
These diagrams demonstrate the amount of water gained by osmosis, and how the rate of osmosis affects the mass of a plant.
Safety Precautions:
When conducting the experiment, the following precautions must be made:
- If a boiling tube is dropped, the glass must be cleaned with a dustpan and brush, and gloves.
- When using the corer, gloves must be worn, as the corer is sharp.
- Throughout the experiment long hair must be tied back and no running in the laboratory.
