- In the late 1500s, early microscopes were developed that allowed the observation of cell structures. In 1665, Robert Hooke discovered cells by examining cork and coined the term "cell". - In the early 1800s, scientists proposed the Cell Theory - that all living things are made of cells. In 1855, it was discovered that cells only arise from pre-existing cells. - Microscopes use different types of radiation (light, electrons) to view cells. Light microscopes use visible light while electron microscopes provide much higher resolution using electron beams.

1. CELL STRUCTURE ALBIO9700/2006JK

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12. Light microscope ALBIO9700/2006JK

13. Carry a Microscope Correctly

14. Images Produced by Light Microscopes Amoeba Streptococcus bacteria Anthrax bacteria Human cheek cells Plant cells Yeast cells

15. Electron microscope ALBIO9700/2006JK

16. Images Produced by Electron Microscopes Cyanobacteria (TEM) Lactobacillus (SEM) Campylobacter (SEM) Deinococcus (SEM) House ant Avian influenza virus Human eyelash Yeast

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26. Comparison of advantages and disadvantages of the light and electron microscope ALBIO9700/2006JK LIGHT MICROSCOPE ELECTRON MICROSCOPE Advantages Disadvantages Cheap to purchase Expensive to purchase Cheap to operate – uses a little electricity where there is a built-in light source Expensive to operate – requires up to 100 000 volts to produce the electric beam Small and portable Very large and must be operated in special rooms Unaffected by magnetic fields Affected by magnetic fields Preparation of material is relatively quick and simple, requiring only a little expertise Preparation of material is lengthy and requires considerable expertise and sometimes complex equipment Material rarely distorted by preparation Preparation of material may distort it Living as well as dead material may be viewed A high vacuum is required and living material cannot be observed Natural colour of material can be observed All images are in black and white Disadvantages Advantages Magnifies objects up to 1500X Magnifies objects over 500 000X Can resolve objects up to 200 nm apart Has a resolving power for biological specimens of around 1 nm The depth of field is restricted It is possible to investigate a greater depth of field