Required practical: osmosis on plant tissue Flashcards
Step 1
Peel a vegetable eg potato to remove skin
This is because the skin can affect osmosis
Step 2
Use a cork borer to produce 3 cylinders of potato in order to have the same diameter
This makes sure all the cylinders are the same diameter
Step 3
Use a scalpel to trim the cylinders to the same length, around 3cm
Step 4
Measure the length and mass of each cylinder using a ruler and top pan balance
Step 5
Place each cylinder into a test tube with 10cm3 liquid
1st = has 0.5 molar sugar solution
2nd = a 0.25 distilled sugar solution
3rd = distilled water
Step 6
Leave potatoes overnight
Step 7
Remove potatoes and remove any surface moisture (DO NOT PRESS BUT ROLL)
Step 8
Measure the length and mass of the cylinders again
Step 9
Calculate percentage increase of the potatoes.
Why use distilled water rather than normal water?
Contains no dissolved substances that affect the rate of osmosis
Why do we roll the potatoes rather than pressing it?
We want to remove surface water not water inside it
Results of distilled water potato
Higher increase in mass as it’s a dilute solution
So water moves into the potato
Result of the 0.5 mol sugar solution potato
Decrease in mass as it’s a concentrated solution so water moves out of the potato into the water
If you were to plot this on a graph, where the line crosses the x axis what does that mean?
No change in mass
So that means no osmosis = concentration outside the cell is same as concentration inside
