Electron Microscope for HSC Biology

An electron microscope lets you see the microscopic world. A world so small it can’t even be seen with light. They need to use electrons to visualise structures such as animal cells and virus’. There are two types of electron microscopes. Scanning electron microscopes (SEM) and transmission electron microscopes (TEM).

Learn about the electron microscope.

Electron microscopes are advantageous over traditional light microscopes since they use electrons instead of photons to render an image of what the specimen being analysed is. The wavelength of an electron can be less then the wavelength of a photon of light hence the better image. However, an electron microscope image will not have colour unless it is rendered.

Scanning electron microscopes (SEM) works by sending electrons at a specimen and then they are rebounded back, kind of like throwing a tennis ball at a wall and letting it rebound back. A detector then determines where the electrons rebound back too. A computer can then analyse this and determine what the surface of the specimen is.

Electron microscope view of a cell

Transmission electron microscope (TEM) is the original electron microscope and uses a high power beam which goes through the specimen, the different pathways different electrons take through the specimen can be determined by the computer. This is put together to create a cross sectional image of the specimen.

Memorise for the exam.

SEMs – surface view – black and white unless rendered

TEMs – cross sectional view – black & white unless rendered

Exam Style Questions.

Question 1.

Compare and contrast scanning electron microscopes and transmission electron microscopes? [4 marks]


Question 2.

Justify the statement “electron microscopes are better then light microscopes” [4 marks]

Question 3.

Label the organelles in the following image and explain whether it is from a scanning or transmission microscope. [6 marks]

Answers.

Question 1.

Scanning electron microscopes (SEM) create a rendering of the image through bouncing electrons off the surface. This creates a detailed image of the surface of the specimen. Whereas, transmission electron microscopes (TEM) passing electrons through the sample. The creates a cross sectional view of the specimen instead. Both generate black and white depictions because they use electrons rather then light allowing for a more detailed image.

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