One particular example is the absorption of water and other nutrients from the soil by root hairs in plants. The following experiments demonstrate these basic concepts in action, and how distribution of substances in two regions with different concenration gradients occurs.
In order to determine osmolarity of a potato and how it is effected by the process of diffusion, a simple experiment is performed. 7 cylindars are carved out from a potato, and then cut to a uniform size of 5 cm. One very important aspect of this experiment are the 6 sucrose solutions, ranging from 0.1 to 0.6 molars, 100 ml each, and placed separately in 6 250-ml beakers together with 100 ml of distilled water. A sensitive balance is also necessary to accurately determine the weight of each potato piece, before and after incubation.
Another experiment is performed to determine the process of osmosis. For this experiment a 500 ml beaker is used which is filled with 300 ml of water. A 25-30 cm dialysis tubing bag is essential, since it represents the semi-permiable membrane that is present during osmosis. 4 ml of a 30% glucose and starch (placed in the dialysis bag) and a small amount I2KI represent diffusing substances. Benedict's reagent is also necessary to determine the diffusion pattern of the substances involved.
The carved out and cut pota...
All the pieces are incubated for 45 minutes, and then their weights are measured and recorded. The percentage change in weight for each of the pieces is also calculated and recorded using the following formula:
Percentage change in weigh= weight change/initial weight * 100
In the second experiment is prepared by soaking it in water, closing one end with a rubber band or string as not to let any solution to enter into the bag, and by adding a 4 ml of a 30% glucose solution into the bag. A 4 ml starch solution is also added, and the color of the glucose-starch solution is recorded. Then, 300 ml of distiled water is placed in a 500 ml beaker in which a small amount of I2KI is added. The color of this solution is also recoded. The dialysis bag is placed in the beaker and they are left for 45 minutes. It should be noted that the free end of the bag is not in contact with the solution of the beaker, as it is left lying out of the beaker. The color of both solutions (in the dialysis bag and beaker) are recorded, after which 3 ml samples are taken from each solution, as well as a sample of distilled water, representing the control tube. Placed in 3 different tubes, a small amount of Benedict's reagent is added to each tube. The final colors are then recorded.
Using the data collected from the first experiment, a graph can be plotted (Table 1). The y axis represents the osmolarities of the sucrose solutions, representing the independent variable while the x axis represents the weight of the potato pieces after incubation, represents the dependent variables, with the negative value being a decrease in potato piece weight, and vise