Required Practical 3 Flashcards
In this investigation you were given potato cylinders taken from potatoes of the same variety. Why was this important
- This is so that cells have the same water potentials
2. No genetic differences
Suggest one way potato skin could have affected osmosis
Potato skin is impermeable to water
Skin is a different tissue
In this investigation you should have use potato cylinders that we’re all the same length suggest and explain one reason why this was important
Same/similar surface area
otherwise it affects the rate of water uptake
Describe how you would use your results for 100% blackcurrant squash to find the rate of osmosis
Find a change in mass
divide by time
Explain why the data above are described as processed results
Calculations are made from raw data
Describe how you would use the students results in the table above to find the water potential of the potato tissue
Plot a graph with concentration on the x axis and percentage change on the y axis
Find concentration where the PERCENTAGE change is 0
Use another resource to find water potential of sucrose concentration where curve crosses x axis
The students give their results as a ratio. What is the advantage of giving results as a ratio.
Allows comparison
Idea that discs have different starting masses
The students were advised that they could improve the reliability of their results by taking additional readings at the same concentrations of sodium chloride. Explain how.
Allows anomalies to be identified
Allows a mean to be calculated
The students used a graph of their results to find the sodium chloride solution with the same water potential as the apple tissue. Describe how they did this.
Draw line of best fit
Find (sodium chloride concentration from the graph) where there is no change in mass
The students were advised that they could improve their graphs by taking additional readings. Explain how
Line of best fit is more reliable
Can plot SD bars
Give three properties of water that are important in Biology
Water is a metabolite Is a solvent Has a relatively high heat capacity Has a relatively large latent heat of vaporisation Has cohesion between hydrogen bonds
Name of method to produce sucrose solutions
Dilution series
A student investigated the effect of SA on osmosis in cubes of potato Describe the method the student would have used to obtain the results in the graph.
Start after all the cubes have been cut, also consider variables he should have controlled
Method to ensure all cut surfaces are exposed to the sucrose solution
Method of controlling the temperature
Method of drying cubes before measuring
Measure mass of cubes at stated time intervals
