Study of Osmosis in Living Plant Tissue

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Objective:
To study osmosis in living plant tissue.

Biological principles:
Water potential is the tendency for water molecules to enter or leave a system by osmosis through a differentially permeable membrane, while osmosis is the process in which water molecules move passively from a region of higher water potential to a region of lower water potential through a differentially permeable membrane. Therefore, potato cells, with their differentially permeable membrane, are selected as the medium for studying osmosis in this experiment. In this experiment, strips are cut from the same potato and placed in sucrose solutions with different concentrations to see if there are any changes in term of weight. Different concentration of sucrose solution is the independent variable while the volume and length of each potato strip and the amount of sucrose solution used are the control variables which should be kept constant. The dependent variable is the percentage change in weight of the potato strips. In addition, it is assumed that the nutrient content of the potato is evenly distributed and all the potato cells are fresh and alive.

Apparatus and materials:
Refer to the lab menu

Procedure:
Refer to lab menu

Discussion:
The potato strips put in distilled water became heavier. This was because distilled water was hypotonic to the potato tissue, so that there was a net movement of water into the cell by osmosis. The weight of potato strips put in 10% sucrose solution increased only slightly because 10% sucrose solution was also hypotonic to the potato tissue, however the water potential difference between the sucrose solution and potato tissue was small. The potato strips put in 20% sucrose solution was hypertonic to the potato tissue. Therefore, more water molecules leaving the tissue resulted in a net movement of water out of the cell by osmosis. The accuracy of the result might be reduced by the errors made during the experiment. For example, the...
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