# Key Concepts Flashcards

What is the independent variable?

The variable that you change

What is the dependent variable?

The variable that you measure

What is the control variable?

The variable that you keep the same

What is the magnification of the eyepiece lens on a light microscope?

10x

What is the equation for working out the magnification of a light microscope?

The magnification of the eyepiece lens multiplied by the magnification of the objective lens. For example if the magnification of the objective lens was 40x then the magnification of the light microscope would be 40x10= 400x

What is the eyepiece graticule?

The eyepiece graticule is a measurement device on light microscopes that has 100 divisions, it has an arbitrary scale and can be used to calculate the length of one epu (eye piece unit) on different magnifications

Hw do you find the value of one epu at a specific magnification (40x)?

- You find the number of epu that corresponds to the number of large divisions on the stage micrometer
- For example if 80 small divisions on the eyepiece graticule corresponds to 18 large divisions on the stage micrometer then the length of the stage micrometer is 180um because each large division on the stage micrometer is worth 10um so 18x10+ 180um
- You then do 180um which is the length of the stage micrometer and divide it by the number of epu (80) needed to make up the length (180um) of the stage micrometer
- So 180/80= 2.25um which is the value of one epu on the 4x objective lens so a total magnification of 40x

What are the uses of staining?

- To highlight a particular organelle eg. the nucleus. Acetic orcein can be used to do this as it stains chromosomes a purple-red colour
- To distinguish between different cell types eg. red blood cells and white blood cells
- To distinguish different tissue types eg. smooth muscle tissue, epithelial etc.

What is the stain for red blood cells?

Eosin

What is the stain for white blood cells?

Haematoxylin

What is the formula for magnification?

Image / Actual