An Investigation to find the Water Potential of Plant Tissue
Benjamin Doughty
Aim:
To find the water potential of plant tissue by investigating the effects of varying concentrations of sugar solutions on the amount of osmotic activity between the solution and potato cylinders.
Hypothesis:
Osmosis is defined as the net movement of water from regions of high water potential to regions of low water potential. This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecules such as water through but does not allow bigger molecules to pass through. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other.
Prediction:
Pure Water has the highest water potential (zero). For this particular investigation I think that the lower the concentration of the sugar solution in the test tube the larger the mass of the potato will be. This is because the water molecules pass from an area of high sugar concentration, i.e. in the water itself, to an area of low concentration, i.e. in the potato chip. Therefore, the chips in higher water concentrations will have a larger mass than in higher sugar concentrations.
Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become "turgid" when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what makes the green parts of the plant "stand up" into the sunlight.
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*** Plan and trial experiment only. The mark has only been awarded for the planning section as no results, conclusion or evaluation have been included. The candidate has planned and carried out a trial experiment and achieved some sound results. To improve more care needs to be taken to ensure all experimental details are included and that tables are recorded clearly with fully labeled headings. There is also some confusion in the relevant background theory which could have been clarified with the inclusion of clear annotated diagrams and some relevant selected material from textbooks or websites. These should be added as references at the end of the report.
