B1.1.3 Light Microscopy

Question 1

How does a light microscope work?

Answer 1

Microscope passes light through an object placed on a slide on a stage
Then through two glass lenses- the objective lens and the eyepiece lense
The lenses magnify the inject so when you view it through the eyepiece, more detail is seen

Question 2

How to observe cells through a microscope (steps 1-7)

Answer 2

1. Move the stage to the lowest position
2. Select the objective lens with the lowest magnification
3. Place the slide which has cells on it, on the stage
4. Raise the stage to its highest position ensuring that the slide doesn’t touch the lens
5. Lower the stage slowly using the coarse focus knob until you see your object - a bit blurry
6. Turn the fine focus knob slowly until your object comes into clear focus
7. To see the cells in greater detail, switch to a higher magnification objective lens without moving the stage. Use the fine focus knob to bring the object into clear focus again

Question 3

Name where on the microscope you would place a head louse to see it in detail

Answer 3

On a slide on the stage

Question 4

Explain why a light microscope has two focusing knobs

Answer 4

The coarse focus is used initially to bring the specimen into view whilst the fine focus is used for precise focusing to achieve clear and detailed images.

Question 5

Formula to calculate total magnification

Answer 5

Total mag = eyepiece lens mag * objective lens mag

Question 6

Why might a scientist stain a cell?

Answer 6

Many cells are colourless so this could make them easier to observe

Question 7

What are the three common stains?

Answer 7

Methylene blue
lodine
Crystal violet

Question 8

What is the function of methylene blue?

Answer 8

Makes it easier to see the nucleus of animal cells

Question 9

What is the function of iodine

Answer 9

Makes it easier to see plant cell nuclei

Question 10

What is the function of crystal violet

Answer 10

Stains bacterial cell walls

Question 11

How to apply a stain (steps 1-4)

Answer 11

1. Place the cells on a glass slide
2. Add one drop of stain
3. Place a coverslip on top
4. Tap the coverslip gently to remove air bubbles

Question 12

State the structures light passes through in a microscope from the object to the eyepiece:

Answer 12

Sample - objective lens - eyepiece lens