Activity #5:

 Orientation: This activity allows students to demonstrate the size relationships of cells, bacteria, viruses, and large molecules. Except for large eggs, cells, bacteria, viruses, and large molecules cannot be seen with the naked eye. Viruses and large molecules are too small to be seen even with a light microscope. The size differences are illustrated by the diagram shown at the top of the "What We Know" section (click here to see again). Instructions: 1.  Note that chart is on a logarithmic scale. That is, each major size marker is 10 times greater than the previous one. For example, 1 cm is 10 times longer than 1 mm, 1 mm is 10 times longer than 100 micrometer (0.1 mm), 100 micrometers is 10 times longer than 1 micrometer, etc. 2.  Assume the following typical sizes for the purposes of this demonstration: frog egg = 10-3 meters (.001 meters or 1 mm) large cell = 10-4 meters (you finish the math on worksheet) large bacterium = 10-5 meters (you finish the math on worksheet) large virus - 10-7 meters (you finish the math on worksheet) large molecule = 10-8 meters (you finish the math on worksheet) 3.  Let a 2 liter plastic cola bottle represent the size of a frog egg. Fill the bottle with water and use a proportional amount to represent the size of each of the other items. Example: a large cell is 1/10 the size of a frog egg, so you would use 200 ml of liquid to represent the size of a large cell. 4.  Calculate how much liquid you would need to represent the size of a large bacterium, a large virus, and a large molecule. 5.  Put the calculated amount in a container so you can actually see the differences in amount. Containers and measuring devices needed: 2 liter cola bottle, a beaker than can hold and measure up to 0.5 liters, a 1 ml syringe (insulin syringe), and a microliter syringe (you could use a 1 ml syringe to estimate but the amount will not be accurate). For the last two volumes of liquid, the amount of water you would need is so small you can just squirt it on a table top.

 Review of the Assignment 1.  Review how you calculated the differences in size 2.  Review how you were able to see the comparison in sizes, using volumes of liquid that were proportional to the size of molecules, viruses, bacteria, and cells.