Understanding relationships:

The following graphing activities will demonstrate the difference between a direct relationship and an inverse relationship.

 Month Temperature (°C) Temperature (°F) Dissolved Oxygen (mg/L) January 10.6 51.1 8.1 February 9.8 49.6 8.2 March 11.9 53.4 7.0 April 13.4 56.1 6.3 May 15.5 59.9 5.0 June 17.8 64.0 4.6 July 21.9 71.4 4.1 August 26.6 79.9 3.1 September 24.8 76.6 3.7 October 21.0 69.8 4.0 November 15.0 59.0 5.2 December 12.2 54.0 6.9

Graph Temperature (oC) on the x-axis and Temperature (oF) on the y-axis.

Notice that these two scales for measuring temperature (Celsius and Fahrenheit) are directly related to one another.  In fact, you can use the following equation to convert from Celsius to Fahrenheit.   oF = 9/5 x oC + 32o

Next, graph Temperature (oC) on the x-axis and Dissolved Oxygen (mg/L) on the y-axis.

Notice that these two factors are inversely related to one another.  As temperature increases, the amount of dissolved oxygen in water decreases.  This relationship is best described by the following equation:  Dissolved Oxygen = -0.29 x  oC + 10.4

Note: the units for measuring dissolved oxygen are milligrams per liter.

Certain organisms require a minimum amount of dissolved oxygen to survive in water.  If water temperature is increased, the amount of dissolved oxygen will be decreased and some organisms will not be able to survive.

1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12

Introduction | Objectives | Pre-Test | Presentation | Activity | Post-Test
PEER Curriculum | Water Quality Modules | Teacher's Pages | Standards