1. Monday, 12 November 2018Monday, 12 November 2018
The electron microscope
Starter: Identify if the following images are taken using a light or electron microscope

2. Light or electron micrograph?
Plant cell

3. Light or electron micrograph?
Yeast cell

4. Light or electron micrograph?
Plant cell

5. Light or electron micrograph?
Testis tissue

6. Light or electron micrograph?
SEM
Hair Lice

7. Light or electron micrograph?
TEM
Plant root
tip cell

8. The electron microscope
Monday, 12 November 2018Monday, 12 November 2018
The electron microscope
Objectives:
Explain how electron microscopes work
Explain the differences between a transmission electron microscope and a scanning electron microscope
Describe the limitation of the transmission and the scanning electron microscopes

9. Early microscopes
Antoni van Leeuwenhoek designed and built over 500 single lens microscopes.
They provided a magnification of 270 times.
Bacteria, protozoa, human blood cells and spermatozoa were discovered using them.
By today’s standards the Leeuwenhoek microscopes are regarded as glorified magnifying glasses.
Single lens sandwiched between two brass plates riveted together.
Specimen holder
Focus adjustment
Screw thread adjustment moves specimen across the field of view.
Front view
Back view

10. Robert Hooke
Robert Hooke described the use of a compound microscope (left) he devised in
He was the first to coin the name “cell” after he observed the angular spaces that he saw in a thin section of cork.
Microscope
Lamp
Mirror

11. Compound microscopes
The compound microscope is a fundamental tool used in biology
High powered light microscopes are used to magnify objects up to times.
They are called compound microscopes because there are two or more separate lenses involved.
Thin and mostly transparent samples are required so that the light from the microscope can pass through the sample easily to reveal the detail.

12. Compound microscope Eye piece lens Objective lens Arm Mechanical stage
Condenser
Coarse focus knob
In-built light source
Fine
focus knob

13. Label the compound microscope
Light source
Diaphragm
Revolving nosepiece
Stage clips
Coarse Adjustment Knob
Base
Body tube
Arm
Stage
Objectives
Ocular lens (eyepiece)
Fine Adjustment Knob

14. The compound microscope

15. A blow fly: actual size - no magnification
Magnification - recap
x5 magnification
Magnification refers to how much larger a sample appears to be compared to its actual size.
As magnification level increases so does the blurriness of the sample.
x20 magnification
Magnification
x50 magnification
Light microscope magnification = x1500

16. Resolution - recap
High resolution
An important factor determining the usefulness of a microscope is its resolving power or resolution.
Resolving power is a measure of the clarity of the image. It is the minimum distance two points can be separated and still be distinguished as two separate points.
E.g. what appears to the unaided eye as one star in the sky may be resolved as two stars with the use of telescope.
Electron microscopes have a greater resolution than optical microscopes because electron beams have shorter wavelengths than those of visible light.
Medium resolution
Low resolution
Fig: Magnification x 100

17. Maximum magnification
Microscopes compared
Use the information cards spread around the room to gather the information you need to complete the table
Light microscope
TEM
SEM
Radiation source
Wavelength
Lenses
Specimen
Maximum resolution
Maximum magnification
Stains
Type of image

18. Maximum magnification
Answers: Microscopes compared
Key differences between TEM, SEM, and light microscopy are outlined below:
Light microscope
TEM
SEM
Radiation source
light
electrons
Wavelength nm
0.005 nm
Lenses
glass
electromagnetic
Specimen
living or non-living supported on glass slide
non-living supported on a small copper grid in a vacuum
non-living supported on a metal disc within a vacuum
Maximum resolution
200 nm
1 nm
10 nm
Maximum magnification
1000 x x x
Stains
colored dyes
impregnated with heavy metals
coated with carbon or gold
Type of image
may be coloured
monochrome

19. The Electron Microscope
I can:
Level:
Outline how an electron microscope works C
Compare and contrast the two types of electron microscope: scanning and transmission B
Summarise the limitations of SEM and TEM A
Keywords: Scanning electron microscope, transmission electron microscope

20. The following information cards should be printed in multiple, laminated and distributed across the classroom so pupils can move around in pairs to view and collect the information to complete the table