Chardakov's Banana Experiment

Chardakov's Banana Experiment

Introduction

The ability of water molecules to move is known as their water

potential. Water molecules always move down a concentration gradient

towards a region of lower water potential, that is, to where there are

fewer water molecules, to where the water potential is relatively more

negative.

As the water potential of one solution decreases, the density of the

solution increases and as the water potential of a solution increases

the density of this solution decreases. This would mean that if at all

mixed, the less dense solution (i.e. the one with the lease negative

water potential) would float on top of the denser solution (the one

with the most negative water potential).

The movement of water molecules down a concentration gradient (from a

higher water potential to a lower water potential) through a partially

permeable membrane is called Osmosis.

Apparatus

* 12 test tubes

* 1 test tube rack

* 1 banana

* 1 knife

* 2 syringes

* 1 square tipped needle

* 1M sucrose solution

* Methylene Blue (stain)

* Water

Method

Put the 12 test tubes into 6 pairs and label one pair 1M, one pair

0.8M, one pair 0.6M, one pair 0.4M, one pair 0.2M, and finally one

pair 0M. Each pair then needs to have 10cm³ of the relevant solution

put into it. For example, the 1M pair of test tubes need 1M sucrose

solution put into them, the 0.8M pair need 0.8M solution put into

them, and so on. However, because there is only 1M sucrose solution

available, the other test tubes need to have diluted solution put into

them. To dilute the solution, you need...

... middle of paper ...

...vour going to one side of the semi-permeable

membrane or the other.

The banana can therefore be said to have had a sucrose concentration

of 0.4M.

Sources of Error

* Surface area of banana may have differed

* Banana may have been bruised or otherwise damaged

* Volumes of solution may have differed

* Number of drops of methylene blue stain may have differed

* May have dropped more than just one drop of stained solution into

the other tube.

* May not have injected stained solution directly in the middle of

the other solution, therefore affecting whether it

hovered/sank/floated.

* Different time for each banana slice in the solutions, allowing

for more osmosis to take place.

* Dilution process may have resulted in mistake of resulting

concentration