Exercise 1 – Potato Change in Mass versus Sucrose Concentrations Introduction: This exercise involves estimating the osmotic concentration of potato tuber cells by using a change in mass method. The null hypothesis states that there will be no change of mass of the potato disks after they have been incubated in any sucrose solution. This means that the concentration of sucrose that the potatoes are in will no effect the movement of water in or out of the potato cells. However, the alternative hypothesis states that the mass of the potato disks will increase after they have been incubated in a hypertonic solution.
The mass of the potato disks will decrease after they have been incubated in a hypertonic solution. After the results have been gathered, appropriate estimations can then be made as to what the osmotic concentrations of the potato tuber cells are. Osmotic concentrations will either be hypertonic, hypotonic or isotonic depending on the results of mass change of the potato tubers. Results: Sucrose Concentraion (mM) Change in Mass (%) 0. 0 0 0. 1 16 0. 2 -34 0. 3 -24 0. 4 -36 0. 5 -26 Table 1: Percentage change in mass of potato disks (%) versus sucrose concentration (mM)
Figure 1: Percentage change in mass of potato disks (%) versus sucrose concentration (mM) The only increase in mass occurred in the sucrose solution with 0. 1 mM (16%). The sucrose solutions from 0. 2 mM to 0. 5 M had a negative change in mass, with the most being at 0. 4 mM at -36%. The trend line (labelled linear series 1) is a negative linear line. Because the percentage change in mass decreased as the sucrose concentration increased, relative osmotic concentration also decreased. Discussion: Since the change in mass of the potato tubers was negative in the sucrose solutions from 0. mM to 0. 5 mM, these solutions were hypertonic relative to the potato dicks. In the solution with only 0. 1 mM of sucrose, the mass of the potato tubers increased which means that this solution was hypotonic relative to the potato disks. From this, it is also logical to conclude that a sucrose solution containing between 0. 1 mM and 0. 2 mM of sucrose will be isotonic because the change in mass of the potato tubers turns from positive to negative in this interval. The change in mass has to be zero for the solution to be isotonic.