DEMONSTRATION OF OSMOSIS IN POTATO TISSUE
Return to see and record the results of this demonstration at the end of the
lesson, or next day.
Note only the presence or absence of liquid.
Do not worry about apparent decay or odd colours, and do not bother
referring to starch.
In answering the following questions, you must be clear about the difference between a
result, i.e. an observation, and a conclusion, i.e. what you think explains it.
(a) What results do you notice and (b) what can you conclude by comparing
potato number 1 with potato number 2?
>(a) Both fill up with liquid
>(b) Sugar and salt have the same effect - causing accumulation of liquid
(a) What results do you notice and (b) what can you conclude by comparing
potato number 1 with potato number 3?
>(a)Cavity in 1 fills whereas 3 stays dry
>(b) Presence of salt causes liquid - i.e. liquid flows uphill, but only if a solution is there
(a) What results do you notice and (b) what can you conclude by comparing
potato number 1 with potato number 4?
>(a)Cavity 1 fills, whereas no 4 stays more or less dry
>(b)Boiling of potato prevents osmosis process - INTACT MEMBRANE required
Where has the liquid in the cavity of some of the potatoes come from? (2
possible answers)
> cells in potato
> water at base
What is happening to the liquid in the dish?
(2 answers, apart from evaporation)
> taken up into potato
> overflowing down the outside
What will happen when the liquid in the cavity overflows?
(answer has 2 stages)
>solute concentration increases below
>flow stops - so it is NOT a PERPETUAL process
Please explain these findings. You may find the following diagram useful.
This animation shows the changes in liquid content within the first two
potato halves.
The graphics below explain the non-appearance of liquid in the other two
cases:
In the case of the 3rd potato half, there is no solute to start the process off so the
cavity remains dry.
The 4th (boiled) potato half has had its cell membranes disrupted by the boiling
process, so water does not pass from cell to cell by osmosis.
Science 8
Potato demonstration of osmosis
Potato 1
Salt
Potato 2
Sugar
Potato 3
Nothing
Name:_Answer key
Potato 4 (boiled)
Salt
water
a) What results do you notice and (b) what can you conclude by comparing
potato number 1 with potato number 2?
>(a) Both fill up with liquid
>(b) Sugar and salt have the same effect - causing accumulation of liquid
(a) What results do you notice and (b) what can you conclude by comparing
potato number 1 with potato number 3?
>(a)Cavity in 1 fills whereas 3 stays dry
>(b) Presence of salt causes liquid - i.e. liquid flows uphill, but only if a solution is there
(a) What results do you notice and (b) what can you conclude by comparing
potato number 1 with potato number 4?
>(a)Cavity 1 fills, whereas no 4 stays more or less dry
>(b)Boiling of potato prevents osmosis process - INTACT MEMBRANE required
Where has the liquid in the cavity of some of the potatoes come from? (2
possible answers)
> cells in potato
> water at base
What is happening to the liquid in the dish?
(2 answers, apart from evaporation)
> taken up into potato
> overflowing down the outside
Science 8
Potato Demonstration of Osmosis
Potato 1
Salt
Potato 2
Sugar
Potato 3
Nothing
Name:______________
Potato 4 (boiled)
Salt
water
1. What results do you notice and (b) what can you conclude by
comparing potato number 1 with potato number 2?
2. What results do you notice and (b) what can you conclude by
comparing potato number 1 with potato number 3?
3. What results do you notice and (b) what can you conclude by
comparing potato number 1 with potato number 4?
4. Where has the liquid in the cavity of some of the potatoes come from?
5. What is happening to the liquid in the dish?