Osmolarity of Fruits and Vegetables

Frankie Doerr, Aubrey Jackson, Kristen French

University of Colorado, Boulder Fall 2008

Vegetables grown in the ground absorb nutrients from the soil. In contrast,

fruit that grow on trees are usually used as vessels to spread seed and do not absorb nutrients through their tissue. Our question stems from this information: will a root growing vegetable have a different osmolarity than fruit that grows on a tree? With this question in mind, we hypothesized that function determines osmolarity.

To test our hypothesis, 0.00 M to 0.35 M solutions of NaCl in increments of 0.05 M were used. The solutions were prepared with standard table salt and 30 mL of distilled water. Five trials were completed, testing for the percent change in weight of uniformly sized cubes of pear, apple, plum, carrot, and potato. In each trial, the masses of eight portions of fruit or vegetable were recorded before and after 2-minute submersions in the NaCl solutions. Before being weighed after submersion, excess water on the exterior of the samples was removed using paper towels. The independent variable in this experiment was the molarity of the salt-water solutions, whereas the dependent variable was the percent change in weight of the given sample. Our controlled variables included the amount of time the samples were in solution, the surface area of the samples, the volume of the solution, and the amount of time that elapsed between removing the sample from the solution and weighing it.

We calculated osmolarities for different fruits and vegetables from the equation for the line of best fit for our data. We found that carrots have the highest osmolarity, followed by apples, pears, plums, and potatoes (1.67M, 1.05M, 0.54M, 0.53M, and 0.25M respectively). When testing whether the vegetables that absorb nutrients have a different osmolarity than the fruits that are used to spread seeds, we found no significant difference between the two groups (p-value = 0.689).

Based upon the p-value we obtained for our t-test, we reject our hypothesis that function determines osmolarity. However, there were many potential problems with our experiment. First, we only tested a very small range of fruits and vegetables, which were quite variable and may not be representative of all fruits and vegetables. Also, we could have introduced additional variability in our results when we attempted to remove excess water from the surface of the samples. If not all of it was indeed removed, or if some water from within the sample was lost to the paper towel, our results could have been less accurate.

To further test this hypothesis, we would need more specific definitions of the function we are testing, as well as what components are contributing to the osmolarity (eg. salt, sugar, other minerals). These concepts could explain some of the osmolarity values that we obtained (for example, a high osmolarity value for apples could be due to the fructose concentration).