RP3- Osmosis

Question 1

Before reweighing, the student blotted dry the outside of each potato cylinder.
Explain why.

Answer 1

• excess water affects mass
• amount of water on each cylinder varies

Question 2

The student calculated the percentage change in mass rather than the change in mass. (2)

Answer 2

• diff. starting mass
• allows comparison

Question 3

The student carried out several repeats at each concentration of sodium chloride solution.
Explain why this is important. (2)

Answer 3

• ignore anomalies → minimise effect of variation in data
• av. ↑ reliable

Question 4

The student used a sharp scalpel to cut the celery. Describe how she should ensure she handled the scalpel safely during this procedure. (2)

Answer 4

1. cut away from body
2. against hard/ flat surface

Question 5

A group of students carried out an investigation to find the water potential of potato tissue.
The table gives concentration of sucrose solution and percentage change in mass of potato cylinders.
Explain why the data in the table are described as processed results. (1)

Answer 5

calculations made from raw data would have recorded initial and final masses

Question 6

A student investigated the effect of surface area on osmosis in cubes of potato.
* He cut two cubes of potato tissue, each with sides of 35 mm in length.
* He put one cube into a concentrated sucrose solution.
* He cut the other cube into eight equal-sized smaller cubes and put them into a sucrose solution of the same concentration as the solution used for the large cube.
* He recorded the masses of the cubes at intervals.
Describe the method the student would have used to obtain the results.
Start after all of the cubes of potato have been cut. Also consider variables he should have controlled. (3)

Answer 6

1. ensure all cut surface of 8 cubes are exposed to solution
2. control temp (eg. water bath)
3. dry before measuring mass
4. measure mass at stated time intervals