Required Practical 3 Flashcards
What is purpose of the calibration curve ?
They are used to determine the concentration of an unknown sample by comparing it to set of standard values with known concentrations
How is a calibration curve used to find the concentration of plant tissue ?
Plot a calibration curve of percentage change in mass against concentration
Find the x intercept where where the plant tissue is is tonic to the sucrose solution
What occurs when plant tissue is placed in a hypotonic solution ?
Water moves out of the plant tissue by osmosis, plant tissue decreases in mass
What are the control variables of this practical ?
Volume of sucrose solution
Size of potato chips
Length of time left in solution
DAB each potato disk with aper towels
What is indicated by the x intercept of the calibration curve
The concentration that is isotonic to the Solution tested
Wp of plant = wp of solution
Outline the procedure of investigating osmosis
Make a simple dilution of 1m sucrose to produce 5 concentrations
Add 5cm t 5 different test tubes
Cut potato into equal sized chips and weigh at the start
Make sure they are fully submerged into the sucrose solution which at a constant temperature
Room temp
Leave for 20 minutes
Take out
Use paper towel to get rid of excess water
Measure mass at regular intervals
Why is percentage used rather than the actual change in mass
Potato chips may not all have the same starting mass
Allows comparison
Why did the student use potato chips from the same potato ?
All cells will have the same water potential
Why is the skin removed from the potato
It has a different water potential
Why did the potato chip left in distilled water gain mass?
They gained mass because water moved into the cells by osmosis. The water moved from a less negative water potential to a more hypertonic negative water potential increasing the mass
