Microscopy

Question 1

Why do we incubate plates inverted?

Answer 1

So that the condensation does not drip from the Petri lid onto the agar.
If it did, the bacteria would move in the pool of liquid and won’t have distinct colonies.

Question 2

What is this part called?

Answer 2

Ocular lens: magnify the object 10x

Question 3

What is this part called?

Answer 3

Objective lens: magnify the object 4, 10, 40, or 100 fold. Multiple this by ocular lens and that’s your true magnification. (1000x fold is maximum magnification for example.)

Question 4

What is this part called?

Answer 4

Condenser lens: focuses the light on the specimen.

Question 5

What is this part called?

Answer 5

Mechanical Stage: holds the microscope slide.

Question 6

What is this part called?

Answer 6

Iris diaphragm: adjusts the amount of light entering condenser.

Question 7

What is this part called? (Top line)

Answer 7

Stage Adjustment: used to move the slide back and forth and laterally.

Question 8

What is this part called? (Middle line)

Answer 8

Coarse focus knob: used to focus when viewing 4x and 10x, NOT 40X OR 100X.

Question 9

What is this part called? (Bottom line)

Answer 9

Fine focus: used for finer adjustment. (Good for 40x and 100x)

Question 10

What is this part?

Answer 10

Lamp brightness control.

Question 11

How do you estimate size of microorganisms in microscope?

Answer 11

Use the pointer body (not tip), using this table. (Width of pointer at base)

Question 12

A 10x objective lens pointer has a width of about what?

Answer 12

~25um.

Question 13

A 40x objective lens pointer has a width of about what?

Answer 13

~6um

Question 14

A 100x objective lens pointer has a width of about what?

Answer 14

~2.5um

Question 15

Define Brownian motion.

Answer 15

Looks like random vibration. It is due to bombardment by atoms.

Question 16

Define Motility

Answer 16

Due to organisms “swimming” and it looks like directional movement by individual cells.

Question 17

What does the dark field do in a microscope?

Answer 17

It enhances the contrast in unstained samples. It works by illuminating the sample which light that will not be collected by the objective lens, and thus will not form part of the image.
Note: The dark field will not work with the 100 X objective lens.

Question 18

What are the five steps for returning your microscope?

Answer 18

1. Remove and return any dark field stop you were using.
2. Lower the stage all the way down and remove any slides still in place.
3. Clean any oil from the objective lenses.
4. Rotate the nosepiece so that the 4x objective is in place.
5. Used to hands when carrying it.