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

Light or electron micrograph? Plant cell

Light or electron micrograph? Yeast cell

Light or electron micrograph? Plant cell

Light or electron micrograph? Testis tissue

Light or electron micrograph? SEM Hair Lice

Light or electron micrograph? TEM Plant root tip cell

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

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

Robert Hooke Robert Hooke described the use of a compound microscope (left) he devised in 1665. 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

Compound microscopes The compound microscope is a fundamental tool used in biology High powered light microscopes are used to magnify objects up to 1500 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.

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

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

The compound microscope

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

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

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

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 400-700 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 250 000 x 100 000 x Stains colored dyes impregnated with heavy metals coated with carbon or gold Type of image may be coloured monochrome

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

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