191104electronmicroscope (1).ppt

8/14/2019 191104ElectronMicroscope (1).ppt

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AS Biology Core Principles

The Electron Microscope



Aims

Resolving powerThe resolving power of light &electron microscopesThe difference between the light &electron microscopeTransmission & scanning electronmicroscopy



IntroductionMicroscopes magnify & resolve imagesMicroscopy began in 1665 when RobertHooke coined the word ‘cells’ to

describe the structure of corkYou need to know about 2 types ofmicroscope - light & electronYou need to know how they work and

the differences between them ‘Its not how much they magnify that iskey - but how well they resolve…’



Resolving Power

The limit of resolution of a microscopeis the smallest distance between 2points that can be seen using a

microscopeThis is a measure of the clarity of theimageA microscope with a high resolving

power will allow 2 small objects whichare close together to be seen as 2distinct objects



Resolving Power

Resolving power is inverselyproportional to the wavelength ofthe radiation it uses



The Light MicroscopeSeries of lenses throughwhich ordinary white lightcan be focusedOptical microscopes cannot resolve 2 points closertogether than about half(0.45) the wavelength ofthe light used (450-600nm)How close is this?



The Light MicroscopeThe total magnification isthe eyepiece magnificationmultiplied by the objectivemagnificationThe maximummagnification of a lightmicroscope is x1500What can it be used for?What can it not be usedfor?



The Electron MicroscopeElectrons (negatively charged, very smallparticles) can behave as wavesThe wavelength of electrons is about 0.005nmWhat will this mean for the limit of resolution?Electrons are ‘fired’ from an electron gun atthe specimen and onto a fluorescent screen orphotographic plateWhere is this technique commonly used?There are 2 types of electron microscopy -transmission and scanningBoth focus an electron beam onto thespecimen using electromagnets



Transmission Electron

Microscope (TEM)In transmission EM theelectrons pass through thespecimen

Specimen needs to beextremely thin - 10nm to100nmTEM can magnify objects up to500 000 timesTEM has made it possible tosee the details of and discovernew organelles - see page 9 inCollins




Microscope (TEM)Cells or tissues are killed andchemically ‘fixed’ in acomplicated and harsh

treatment (in full detail in table3.1 pg 52 Rowland)How does this differ to lightmicroscopy?This treatment can result inalterations to the cell - knownas artefactsWhat will this mean for theimages produced?




Microscope (TEM)

Transmission electronmicrograph ofepithelial cells from arat small intestine.Scale bar = 5 mm.



Scanning Electron

Microscope (SEM)In Scanning EMmicroscopes theelectrons bounce offthe surface of thespecimenProduce images witha three-dimensionalappearanceAllow detailed studyof surfaces



Scanning Electron

Microscope (SEM)Now watch the following clip explaining SEM



Scanning Electron

Microscope (SEM)



Links

www.learn.co.uk/

www.microscopy-uk.org.uk/intro/index.html

www.mwrn.com/feature/education.asp

http://www.feic.com/support/tem/transmis.htm

http://anka.livstek.lth.se:2080/microscopy/foodmicr.htm

http://www.learn.co.uk/

http://www.microscopy-uk.org.uk/intro/index.html

http://www.mwrn.com/feature/education.asp









http://www.mwrn.com/feature/education.asp




http://www.learn.co.uk/



Light & Electron Microscopes

Feature LightMicroscope

ElectronMicroscope

Radiation used

Radiation source

Nature of lenses

Lenses used

Image seen

Radiation medium

Magnification

Limit of resolution

What it can show

Copy & complete the following table



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191104electronmicroscope (1).ppt

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