Microscopy

Question 1

How do light microscopes work and what do they let us see?

Answer 1

• Use light and lenses to form an image of a specimen and magnify it.
• individual cells + large sub cellular structures like nuclei

Question 2

How do electron microscopes work and what can we see?

Answer 2

• Use electrons instead of light, have much higher magnification than light microscope and have higher resolution giving sharper image.
• They let us see smaller things in detail like internal structure of chloroplasts.

Question 3

What is the formula for magnification?

Answer 3

image size / real size

Question 4

What is the formula for real size?

Answer 4

Image size / magnification

Question 5

How do we work out image size?

Answer 5

magnification x real size.

Question 6

Suggest why you might add stain (iodine) to a microscope slide

Answer 6

To highlight objects in the cell

Question 7

Name steps in onion cells practical

Answer 7

1) Add a drop of water to middle of a clean slide
2) Cut up and onion + separate it into layers
3) Use tweezers to peel off epidermal tissue from a layer
4) Place epidermal tissue into the water on slide
5) Add a drop of iodine solution
6) Place a cover slip on top - avoid trapping air bubbles as obstructs view of specimen.
7) Clip slide onto stage
8) Select lowest powered objective lens
9) Use coarse adjustment knob to move stage up to just below objective lens
10) Look down eyepiece, use coarse adjustment knob until you get a clear image of slide.
11) Switch to high powered objective lense if slide needs greater magnification.

Question 8

A cheek cell is viewed under a microscope with x40 magnification. Image of cell is 2.4nm wide. Calculate real width of the cheek cell.

Answer 8

2.4 / 40 = 0.06

x1000=60nm