OBJECTIVE: The student shall demonstrate their ability to use the microscope by correctly determining the size of a number of organisms on prepared slides or living cultures.
PURPOSE: How large is one cell compared to another? Size is as important in the micro world as it is on our own visible world.
SET: [Borrowing an overhead from the GAMETES lesson, show students a list of relative sizes in the microscopic world] How large would a bacterium under 10x or even 40x appear? How would it compare to a human egg? A frog egg? How can we calibrate our microscope in order to it use for measurement estimates?
MODEL: demonstrate, using the overhead, how to determine size under the microscope, by:
1). Determine the field width for the 10x objective
2). Use the 10x field width to calculate the field widths for the other objectives
3). Use the above information to determine an organism's size.
STRUCTURED PRACTICE: Draw an organism on your overhead and have the students help you determine its size. You may need to do this with several imaginary organisms.
GUIDED PRACTICE: Pass out "clear" mm rulers. Make sure everyone is on the lowest power and that they are thinking in terms of proportion.
CLOSURE: Using the field diameter of an objective/eyepiece combination is one way to attempt to measure an unknown object/organism. What would be a better way?
NOTES: This lesson is deceptively difficult for many students.