CPAC 3 Flashcards
Method
- Use a cork borer to cut 5 potato cylinders of the same diameter
- Use a scalpel and ruler to trim each potato cylinder so they are all the same length
- Measure the mass of each potato cylinder and record in a table of results
- Label six boiling tubes 0,0.2,0.4,0.6,0.8,1.0 dm^-3 sucrose and make up a dilution series
- Put the potato chips into each of the tubes and leave for a set amount of time in a water bath set around 30º.
- They are then removed and dried to remove excess liquid
- The final length and mass of each potato cylinder is then measured and recorded
How to calculate percentage change
((Final mass -initial mass)/ initial mass ) x 100
What does a positive percentage change suggest
Indicates that the potato has gained water by osmosis meaning the solution had a higher water potential than the potato which would make potato cells turgid as the water exerts turgor pressure
What does a negative percentage change suggest
The solution had a lower water potential than the potato, the potato cylinder in the strongest sucrose concentration will have decreased in mass the most as there is the greatest conc. gradient which means more water molecules will move out of the potato cells by osmosis making them flaccid
Graph intercept
The pointer at which the line of bees fit crosses the x-axis is the concentration of sugar inside the potato as this is where there would be no change in the mass of the potato
What occurs when plant tissue is placed in a hypotonic solution
Water moves into the plant tissue by osmosis, plant tissue increases in mass
What occurs when plant tissue is placed in a hypertonic solution
Water moves out of the plant tissue by osmosis, plant tissue decreases in mass
Why are the potato chips dabbed dry after removing from the sucrose solution
To remove any excess water clinging to its surface
What are the controlled variables of this practical
Volume of sucrose solution
Size of potato chips
Length of time left in solution
DAB each potato disc with paper towels
