Osmosis

Question 1

(Osmosis required practical)
The carrot cylinders were left for 18 hours in sucrose solution.
Explain why they were left for so long
1 mark

Answer 1

It has reached equilibrium
no further / maximum change in length

Question 2

Young carrots store sugars in their tissues but, in older carrots, some of this is converted to starch. How would using cylinders of tissue from older carrots affect the results obtained for a sucrose solution of 0.6 mol dm-3? Give a reason for your answer.
2 marks

Answer 2

Greater decrease / length smaller;

More water removed;

Greater difference in water potential / cell with higher / less negative water potential;

Starch is insoluble / has no effect on osmosis

Question 3

The student carried out several repeats at each concentration of sodium chloride solution. Explain why the repeats were important. 2 marks

Answer 3

(Allows) anomalies to be identified / ignored / effect of anomalies to be reduced / effect of variation in data to be minimised.

Makes the average / mean / line of best fit more reliable / allows concordant results;

Question 4

When looking in errors in a table, what should you look for?

Answer 4

If rounded to the same number of decimal places

If IV/ name of solution is the first column

Question 5

Suggest and explain an advantage of carrying out this investigation at 30 degrees rather than 20 degrees

2 marks

Answer 5

Warmer water at 30 degrees has more kinetic energy (1)

More/ quicker osmosis
Or
Large diffusion in mass (1)

Question 6

The student concluded from the information in the table above (final mass is higher than initial mass) that the water potential of the solution inside the egg is higher than the water potential of the vinegar.

Is the student’s conclusion correct? Justify your answer. 3 marks

Answer 6

Conclusion incorrect

1. Egg mass increased;
2. Water moves in by osmosis;
3. (So) egg water potential lower (than vinegar water potential)
   OR
   Vinegar water potential higher (than egg water potential);

Accept less negative for “higher”
OR
“more negative” for lower

Question 7

The student wanted to determine the water potential of chicken eggs.
She produced a dilution series of sugar solution followed the procedure described above of covering the eggs with solution.

She calculated the final mass to initial mass ratio of the egg covered in each sugar solution

How would you advise the student to use her calculated ratios to determine the water potential of the eggs?

In your answer state the independent variable in the student’s investigation.

4 marks

Answer 7

Independent variable
1. Concentration of sugar solution (1)
Determines the water potential

2. Plot calibration curve (1)
3. Interpolate from ration of 1 (1)
4. Change concentration into water potential (1)

Question 8

The student produced the sucrose solutions with different concentrations from a concentrated sucrose solution.

Name the method she would have used to produce these sucrose solutions.

Name of method

1 mark

Answer 8

Dilution series

(Can accept serial dilution)

Question 9

Explain the result for the chip in 0.8 mol dm sucrose solution.

Intial mass - 2.72g
Final mass - 2.20g

2 marks

Answer 9

1. (0.8 mol dm sucrose) solution has a more negative / lower water potential than potato (cytoplasm);
   OR
   potato (cytoplasm) has a less negative / higher water potential than (0.8 mol dm 3 sucrose) solution;

(Accept sucrose solution is hypertonic/ potato cytoplasm is hypotonic)

2. (therefore) water moves out (of potato) into the (sucrose) solution by osmosis (so cells decrease in mass);

(Accept water move down water potential gradient)