🔬 Cells and microscopy

One of the unifying concept in biology, that is the cell, has been arrived upon in big part thanks to microscopy. Additionally, microscopes have enabled the accumulation of knowledge about the cellular components i.e. organelles. Microscopes use visible light, as well as electrons and lasers to produce images of very small specimens prepared on slides, often dissected in a specific manner and stained with dyes, some fluorescent.


You will need to know about the difference between light, transmission electron and scanning electron microscopes – LM, TEM and SEM. Both the latter (as the name suggests) use a beam of electrons, rather than light, to produce an image of the sample.


TEM uses electrons which pass through the sample, so the resulting micrograph (image) shows everything within the sample in black and white, for example organelles in a cell. SEM uses electrons which scan the sample in 3D, resulting in a coloured micrograph with 3D detail, but no components from within the sample.


In light microscopy, light does go through the sample, but the outcome depends on the thickness of the sample. For example, the plant root slice in the diagram (LM) is thin enough to be able to see through the thickness of the sample. Light would also travel freely through air but not…