Investigating the Concentration of the Solutions Inside the Vacuole of a Potato Cell.

Osmosis Investigation

We are trying to find out what the concentration of the solutions is inside the vacuole of a potato cell.

We will investigate how the mass of the potato chips change in different sucrose solution concentrations.

We will use osmosis to do this.

I will be measuring and controlling many different variables, these include; -

The dependent Variable - Weight of potato chip

Independent Variable - Concentration of sucrose

Control Variables consist of; -

1. Temperature

2. Surface area of potato

3. Volume of sucrose solution

4. Same time for each potato chip submerged in solution

5. Potato chips all from same potato

The effects on the dependent variables all differ; here is how the main variables in my experiment work out.

Variable Effect on Dependent Variable

Surface area of potato chip The greater the surface area the more water it will be able to absorb

Same chip from the same potato The genetic make-up will be the same and therefore the partly permemble membrane will be similar

Time left in the solution The longer spent in solution the more that is absorbed

Coating on the potato chips If not rinsed off and dried after a certain period of time the chips will form a coat of sugar thus decreasing surface area

Quantitative prediction

I predict that the effect of changing the sucrose concentration will be that as the concentration of the sucrose solution increases, first of all the mass of the chip will increase, and then the change in mass will gradually decrease until mass is lost and this mass loss will gradually increase in amount.

Because when the sucrose concentration is low, the concentration of water outside the cells of the potato chips will be greater than that inside, and therefore water will osmosis into the cells of the chip which will gain mass. As the concentration of sucrose increases the concentration of water outside the call will eventually become less than inside the cells of the chip and mass will be lost.

Dependent

Variable

Inside the cells Outside the cells

Dilute solution Concentrated solution

Higher water concentration Low water concentration

Key:

= Sucrose particle

= water molecule

= osmosis

= partially permeable membrane

In the higher sucrose concentration solution, the net movement of water (osmosis) is to the outside of the cell, and the chip will lose mass, the cells will become plasmolysed.

The chip in a low concentration of sucrose solution, is the opposite of the diagram above, in that the water osmoses into the cells of the chip, mass it gained, through osmosis of water into the plant cells, the cells will become turgid.

Because I am measuring osmosis, I will try to keep constant the other that affect osmosis, those other than the concentration of sucrose and water, I will be using potato chips from the same variety of potato (assuming that the genetic make-up and therefore partially permeable membranes will be more similar in make-up). I will use the same volume of solution at each concentration of sucrose solution, that being 20ml3. I will leave the potato chips in solution for the same time at each solution concentration. I will use the same method at each concentration, and for each potato chip individually, in that I will dry the excess water off the chips in a similar manner, and use the same accuracy of the weighing scales, prepare the chips for use in the same way and other aspects. I will keep the surface area of the chips as constant as possible, this being that I will use chips of the same cross sectional area and length. I found in my preliminary work that the chips in the higher concentration of sucrose solution tended to float thus excluding a certain part of their cross-sectional area from the solution, I do not know how to stop this. I will carry out all of my experimental work at room temperature and thus temperature will not affect my experiment. The time will not effect my results because I plan to leave my chips in solution for 30 minutes at each concentration, I discovered that significantly enough results were obtained after this length of time in my preliminary work.

What I plan to do.

I plan to cut out 12 potato chips into cubes of uniform diameter, using a scalpel, and they won't be at a specific size, although they will all be of a unison length and width with the same surface area.

N.B. They will be the same size as I used in my preliminary work.

I will place 2 of each of these chips into each concentration of sucrose solution, and leave them in for a time limit of 30 minutes once the time is up I will rinse of the sugar coating that will form over the potato chips thus minimizing the surface area. Then weigh and record their weight.

I will have weighed them before potting them into the solution, and I will weigh