An investigation of the glucose concentration of the cell sap in potato cells

An investigation of the glucose concentration of the cell sap in potato cells

In this experiment I intend to investigate the effects of osmosis on potato cells. Specifically, I intend to use my knowledge of osmosis to investigate the glucose concentration of the cell sap in potato cells.

Osmosis is a method by which water levels on either side of a semi permeable membrane may balance themselves. It occurs between regions of high water concentration and low water concentration. As it is a special method of diffusion exclusive to water, it also allows dilute and concentrated solutions to balance their strengths. It does this by preventing large non-water particles from passing through the semi-permeable membrane due to their size, in order that the water levels on either side may equate, regardless of the solution's other contents. Osmosis is passive, that is to say it does not require energy in order to be performed. This is because it occurs solely between regions of high and low water concentration.

The direction and speed of osmosis depends on the two solutions' osmotic potential. This is the measure of the pressure by which the water molecules of a solution diffuse across a semi-permeable membrane. A solution's potential is defined by its concentration. The more soluble a solution has in it, the lower its water concentration and the lower its osmotic potential. In the example below sugar molecules represent the soluble.

Cell sap is contained in the vacuole of a cell and is a part glucose, part water solution. The membrane of the cell acts as a semi-permeable membrane across which osmosis occurs (see below). In the case of osmosis into and out of the vacuole, it occurs across two membranes - the plasmalemma and the tonoplast. When osmosis occurs, water may enter or leave the vacuole according to the concentration of the substances inside and outside the potato cell. In the example below we see what would happen if a plant cell were surrounded by pure water.

As pure water has the highest water concentration possible, osmosis will invariably occur into the cell vacuole, which by definition contains a solution lower water concentration.

The plant cell will take in as much water as is needed to make the water levels on either side of the membrane equal. As the glucose molecules cannot pass out of the cell to equate the water levels, the volume of cell sa...

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...order to obtain a wider and more precise base of evidence.

There is scope for further investigation of the topic in order to obtain further evidence and draw a more accurate conclusion. For example, now the concentration of potato cell sap has been identified at about 15%, a smaller range of solution strengths could be used in an otherwise identical experiment; 5 solutions of 10% and 20% concentration for example. Alternatively, investigations could be conducted into the effects of osmosis on different vegetables or more widely plants in general. For further information on the potato, the same experiment could be conducted using samples from different parts of the plant. This would establish whether different areas of a plant have differing levels of sucrose in their cell sap. Any of these suggestions would both help to support my conclusion and extend the investigation in general further.

Bibliography

- GCSE Biology D. G. Mackean

- Biology for You Gareth Williams

- The Times GCSE Revision Guides - Biology PC CD ROM

- Hutchinson's Multimedia Encyclopaedia PC CD ROM

- www.britannica.com

- www.bbc.co.uk/education

- www.homeworkhigh.com/science

- www.learn.co.uk