To determine the concentration of the cell sap in potato storage tissue. By using Osmosis, determine what the sugar concentration of cell sap is.

Biology Coursework

Emmeline Hastings

Aim: To determine the concentration of the cell sap in potato storage tissue. By using Osmosis, determine what the sugar concentration of cell sap is.

Prediction

I predict that the potato segment in the distilled water will definitely gain in weight because the solution outside it has a much higher concentration of water then in the cell sap meaning Osmosis will occur and the potato segment take in water. I predict that 0.2M sugar solution will also gain weight because it still has quite a high concentration of water outside the potato. The potato in the 0.4M solution will gain weight but the potato in the 0.6M and 0.8M solutions will lose weight. The glucose concentration of the cell sap will be between 0.4M and 0.5M.

Scientific Knowledge

This experiment is based on the concept of Osmosis. Osmosis is the diffusion of water molecules from a region of high water concentration to a low water concentration through a semi permeable membrane (in this case, the cell potato cell membrane). The cell walls of the potato cells are semi permeable meaning that water molecules (which are small) can fit through but other bigger molecules such as glucose cannot pass through. The water molecules can flow both ways through the membrane, letting molecules both in and out.

The Kinetic theory states that all molecules of every substance have energy which causes them to move about for example a chemical reaction can be accelerated through heating because the molecules gain more energy efficiently causing harder and more effective collisions of the molecules. In water the molecules have energy which makes them move, it is this energy which powers Osmosis and allows water molecules to pass through the semi permeable membrane.

The experiment uses Osmosis to make an estimation of the concentration of the cell sap in the potato storage tissue. The cell sap is a solution mainly of water, sugar, starch and salts. By surrounding the potato in a created sugar solution we can use osmosis to determine which solution has a higher or lower concentration of water, the cell sap or the solution outside the potato. This is because if the solution outside the potato piece had a lower concentration of water i.e. had less water than the solution inside the potato storage tissue, water would move outside the potato into the artificial sugar solution as if to dilute it. Like it wants to ‘balance out’ the water concentration on either side of the cell walls. This is what Osmosis aims to do, allow water to flow in and out in order to achieve an equal concentration of water on either side of the semi permeable membrane. Once it has done this it is called Net flow, or a dynamic equilibrium. This is basically when the same amount of water molecules coming in is the same as the number of water molecules going out. If the solution outside the potato had a higher water concentration then that inside the potato, water would move into the potato making it larger. By monitoring the size of the potato we can determine what solution had the higher concentration. If no change is made then the concentration of the solution outside the potato is identical to the concentration of the solution inside the potato.