Diffusion with Surface Area to Volume Ratio

Introduction

Cells have to interact with their environment, chemicals and water and in order to do so they must be able to move across the cell membrane and the cell. The movements within a cell are called Diffusion. When molecules move across a cell membrane it is known as Osmosis. Diffusion is the process by which molecules of a substance move from areas of higher concentration of that substance to areas of lower concentration. Diffusion can be the transfer of anything anywhere. However, that is not true for osmosis. Osmosis is diffusion, but a specific type of diffusion. Osmosis is only the diffusion of water molecules through a selectively permeable membrane and a concentration gradient. Only certain molecules can cross the membrane to either go in our out of the cell.

If outside the cell there is a lower concentration of molecules than inside the cell, it is called hypotonic and water will move from outside the cell into the cell. If the solution outside the cell has a larger concentration of dissolved materials the solution is hypertonic, so the water would move from the cell into the solution.

Aim

The aim of this experiment was to verify the concept of Osmosis and Diffusion with a semi-permeable membrane (dialysis tubing), it will be exposed to different environments and concentration gradients.

Hypothesis

I thought that that dialysis tubing would end up weighing more as there would be less water and more molecules within the tubing so water would move through the semi-permeable using a concentration gradient into the cell.

Variables

Independent Variable - Solution

Dependent Variable - Weight of the dialysis tubing

Controlled Variable - Length of dialysis tubing

- Amount of substance in each of the tubes

- Amount of water in the beakers

` - Measuring in the same measurement

- Time between each weighing session

Unable to control Variables - Temperature in room and beaker

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Materials

* 4 - 4" pieces of dialysis tubing and string

* 4 - 250 mL beakers

* Distilled water

* Egg white

* 10% salt solution

* 20% sucrose solution

* 10% starch Solution

* String

* Balance

* Paper towels

Procedure

Method

To start off with, 6" of dialysis tubing was cut and soaked in water and then tied at the bottom of the tube with a piece of string. You then add 2" of 10% Salt solution into the tube, and close the top end of the tube, fold it and tie a string over the top so it is fully sealed. Once done we cleaned the outside of a tube by rinsing it and then using paper towels to dry it. These steps were repeated for the egg white, sucrose and starch solutions. Then immediately weigh the tubes on