Visualizing changes in solute concentrations: Graphing the data Variables that change continuously can be visually represented in line graphs. An electrocardiogram of blood pressure as the heart beats, or blood insulin levels during a glucose tolerance test, are two common examples. Solute concentrations across membranes also change continuously over time due to osmosis and other factors, so line graphs are useful ways to visualize the changes. Remember that line graphs need to have some basic components to them: Data. Usually data are collected at discrete points, and the individual points are plotted and then connected by a line. • Legend. If more than one line is represented on a graph, a legend is needed to define the different lines. ● X-Axis. Horizontal (flat) axis representing the independent variable, the factor being tested according to the hypothesis. Y-Axis. Vertical (up and down) axis representing the dependent variable, which is measured, as is expected to change due to the independent variable. One classic lab performed in general biology classes is to take regular chicken eggs and dissolve their shells by placing the eggs in an acidic solution (usually vinegar; you could do this at home!) overnight. The remaining soft membrane and white and yolk inside the egg make for a nice model of a cell that's visible to the naked eye. This cell model can be used to observe osmosis and the effects of different solute concentrations on osmosis firsthand. Usually 3 eggs are used, and 1 each placed in hypotonic, isotonic, and hypertonic solutions. Below are data collected from this experiment². Use the data and the graph to answer the following questions. Time (min) 0.00 15.00 30.00 45 60 ом 0.00 0.20 0.45 0.75 1.1 % Mass change 0.8 M 0.00 0.01 0.02 -0.01 0.01 2 M 0 -0.65 -1.4 -1.95 -2.55 Percent change in egg mass 2 1 -2 -3 0.00 Change in egg mass over time 20.00 Time (min) 40.00 60.00 4. What solution molarity was the egg placed in represented by the yellow, starred points? the blue square points? the green circular points? 5. How long did it take the egg placed in the 0 M solution to increase its mass by about 1% due to osmosis? 6. How long did it take the egg placed in the 2 M solution to decrease its mass by about 1% due to osmosis? 7. Which line represents the hypotonic, isotonic, and hypertonic environments? Explain how this is evident from the graph.