Activity 5B: Tonic Water Hyper and Hypo

Each student should receive two pieces of a high water-content vegetable such as eggplant, squash or beet. The vegetable pieces should be blotted dry with the paper towels and weighed. Honey (represents sugar) should be sprinkled onto one of the vegetable slices (the one without honey is the control sample). (Approximately 1/4 of a teaspoon of honey with a slice of zucchini squash which is one inch across works well!) The students should record what they observe at the beginning (time = 0), and then at five minute intervals for 15–20 minutes. The honey will extract the water from the vegetable; the water will accumulate on the surface of the vegetable and be readily visible. This demonstrates how the high sugar content of blood in a diabetic extracts water from the body’s tissues, resulting in frequent urination and dehydration. The vegetable can be toweled off, so that students can further observe the water that was being extracted from the vegetable and weighed again. Point out that the sugar has the same drying effect that salt has. Students will make a graph to determine the rate of water loss in the zucchini.

 

In this part of the activity, students will quantify the rate of osmosis in

zucchini or other high-water content vegetable. Students will place one

piece of zucchini in distilled water and another piece of zucchini in concentrated sugar water. They will observe the change in mass over time

and determine the rate of osmosis in both vegetable samples. They will

make a graph of their data and draw conclusions about their observations. The rate of osmosis between Part I and Part II can be compared.