Osmosis into Potato Tissue

Osmosis into Potato Tissue

Aim: To investigate how varying the sucrose concentration around piece

of potato tissue affects the diffusion of water (osmosis) into or out

of the cell.

Introduction:

Definition of Osmosis: This is the diffusion of water molecules from

an area of high water concentration (dilute solution) to an area of

low water concentration (concentrated solution) through a permeable

membrane.

The rate, again, depends on the surface area, the concentration

gradient and the properties of the partially permeable membrane.

A diagram of Osmosis:

[IMAGE][IMAGE]

Text Box: =Water

Text Box: =Solute (e.g. Sucrose)Text Box: Low ConcentrationText Box: High concentration[IMAGE]

[IMAGE]

[IMAGE]

We have looked into osmosis previously in the experiment of turgid and

plasmolysed onion cells, and a visking tube.

[IMAGE]

Demonstration of Osmosis Using a Visking Experiment

[IMAGE]

[IMAGE]

[IMAGE]

[IMAGE]

The Visking tube experiment was used to demonstrate osmosis. The

Visking tubing was semi-permeable, which allows small molecules

(water) to pass through, but it doesn’t allow the larger ones (sugar).

Apparatus

* a small length of capillary tubing

* a larger amount of Visking tubing

* 0.5 sucrose solution

* pipette

Osmosis Experiments

Factors that will affect the rate of osmosis will be the Independent

variables, the dependent variables and the external variables.

Independent variable =

Concentration of sucrose solution – If the sucrose solution is

changed, osmosis will change in rate and direction.

Dependent variables =

Change in mass of potato.

(Water movement in and out)

External variables =

Size and shape of potato – If the potato is large in surface area then

osmosis will occur more.

Volume of solution– If the sucrose solution is much higher this will

affect osmosis.

Temperature – if it is warmer then osmosis will happen more rapidly.

Type of potato – In a fair test you must use the same potato other