Effect of osmosis and sugar concentration on the mass of plant tissue: analysis | Combined science

Starter quiz

Match each variable to the correct example when investigating the effect of sugar solution concentration on potato chips.

independent variable

⇔

concentration of sugar solution ✓

dependent variable

⇔

mass and length of potato chips ✓

control variable

⇔

temperature of the solutions ✓
When investigating the effect of sugar solution concentration on potato chips, which piece of apparatus was used to control the temperature?

boiling tubes

timer

thermometer

water bath ✓
At which concentration did the potato chip decrease in mass?

0.25 mol/dm $^3$

0.50 mol/dm $^3$

0.75 mol/dm $^3$

1.00 mol/dm $^3$ ✓
Which concentration caused the potato chips to lose water by osmosis?

0.25 mol/dm $^3$

0.50 mol/dm $^3$

0.75 mol/dm $^3$

1.00 mol/dm $^3$ ✓
Whose prediction is correct?

Lucas: Potato chips will gain mass in the most concentrated solutions.

Sam: Potato chips will lose mass in the most concentrated solutions. ✓

Laura: The most concentrated solutions will have no effect on the potato chips.
Water can move out of and into potato chips because the potato cells have a selectively-______ membrane.

'permeable' ✓

Exit quiz

Calculate the change in mass, in grams (g), for the potato chip in sugar solution at a concentration of 0.25 mol/dm $^3$ .

'+0.07' ✓
Calculate the percentage change in mass (%) for the potato chip in sugar solution at a concentration of 0.25 mol/dm $^3$ . Give your answer to 2 decimal places.

'+2.75' ✓
Why is it necessary to calculate the percentage change in mass before comparing the effect of concentration on the potato chips?

Calculating the percentage is a more scientific measurement.

Not all the chips have the same final mass.

Not all the chips have the same initial mass. ✓

The percentage is closer to the true value.
Calculating the percentage change in mass helps to remove __________ error from the results.

calculation

percentage

random ✓

systematic
Match each direction of water movement to where it is shown on the graph.

net movement into potato chip cells

⇔

when the line is above the x-axis ✓

net movement out of potato chip cells

⇔

when the line is below the x-axis ✓

no net movement

⇔

when the line crosses the x-axis ✓
Which point on the graph enables us to estimate the concentration of sugar inside the potato chip cells?

The point on the line where the change in mass was the most positive.

The point on the line where the change in mass was the most negative.

The point where the line crosses the x-axis. ✓

The point where the line crosses the y-axis.

Worksheet

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Presentation

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Video

Lesson Details

Key learning points

Plotting and interpretation of a graph showing the effect of sugar concentration on the mass of potato tissue.
Increase in potato mass means water moved in by osmosis (because the sugar solution was more dilute outside).
Decrease in potato mass means water moved out by osmosis (because the sugar solution was more concentrated outside).
The concentration of sugar in the potato tissue can be determined from the point at which there was no change in mass.
At this point the sugar concentration was equal inside and out, so there was no net movement of water.

Common misconception

Mistakes around calculating change in percentage mass are common, as are misunderstandings around why changes in mass occur.

The calculations for percentage mass are introduced and walked through with an 'I-do, we-do, you-do' model. There are plenty of calculations to practice on. Why mass changes occur is also covered in detail and with supporting diagrams.

Keywords

Osmosis - the net movement of water molecules through a selectively-permeable membrane from a dilute solution to a concentrated one
Net movement - the overall movement of particles
Random error - causes results to differ by different amounts due to a factor other than the independent variable (the factor we changed)
Concentration gradient - a difference in the concentration of particles from one area to another