Required Practical Activity 3 - Investigate the effect of a range of concentrations of salt or sugar solutions on the mass of plant tissue

Question 1

What is the apparatus needed for investigating the effect of a range of concentrations of a range of salt or sugar solutions on the mass of plant tissue?

Answer 1

• Potato
• Cork bearer
• Ruler
• Distilled water
• Sharp knife/scalpel
• White tile
• Paper towels
• Mass balance
• Five Petri dishes with labels
• Five different concentrations of sugar solution (0.00, 0.25, 0.50, 0.75 and 1.00M)

Question 2

What is the method for investigating the effect of a range of concentrations of a range of salt or sugar solutions on the mass of plant tissue?

Answer 2

1. Use a cork borer to cut five potato cylinders of the same diameter.
2. Use the knife to trim off any potato skin on each potato cylinder. Then trim each potato cylinder so that they are all the same length.
3. Accurately measure the mass of each potato cylinder.
4. Accurately measure the length of each cylinder.
5. Record your measurements in a table.
6. Measure 10 cm3 of each concentration of sugar or salt solution and put into petri dishes. Label each boiling tube clearly.
7. Measure 10 cm3 of the distilled water and put into the fifth boiling tube. Label the petri dishes clearly.
8. Add one potato cylinder to each petri dish.
9. Leave them in there for 30mins
10. After 30 mins remove them, dry them using paper towel
11. Re weigh them to record final mass
12. Calculate the change in mass and percentage change in mass

Question 3

What is the conclusion for investigating the effect of a range of concentrations of a range of salt or sugar solutions on the mass of plant tissue?

Answer 3

In solution 0 mol/dm³ we saw an increase in the mass of the potato. This means that water moved into the potato. A solution of 0 mol/dm³ is pure water, we can say it is a dilute solution so water moved via osmosis from a dilute area outside the potato through the partially permeable membrane into the potato. This means that 0 mol/dm³ was a hypotonic solution.

In solution 0.5 mol/ dm³, there is now sugar dissolved in the water, this makes it more concentrated. We saw a decrease in the mass of the potato, this means that water moved out of the potato. Water moved via osmosis from a dilute are inside the potato to a more concentrated solution. This means that 0.5 mol/ dm³ was a hypertonic solution.

As the solutions became more concentrated, we saw increasingly more water leave the cell, this is because water moved from a more dilute area inside the potato chip to a more concentrated solution outside the potato chip via osmosis causing the potato chips to decrease in mass.

Question 4

How do you calculated % change?

Answer 4

% change = (change in value / original value) x100

Question 5

2 sources of error:

Answer 5

• crying of chips
• conc of solution
• accuracy of balance
• evaporation from tubes