Introduction

LM, TEM and SEM

Resolution and magnification

Staining

Structure of Eukaryotic versus Prokaryotic

Introduction

I once rescued my biology grade back in secondary school in Romania by knowing the definition of a cell.

“The cell is the structural and functional unit of living things” I wrote. I wasn’t far off was I?

So yes, the cell is the unit of life. It’s a delimited volume where the chemistry of life can happen. In unicellular organisms, the cell is themselves, the body, the whole, the organism.

LM, TEM and SEM

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 various materials of high opacity.

When talking about microscopes, differentiating between resolution and magnification is important. In principle, it’s not hard to understand. Imagine zooming in a photo to try to see a detail. That is magnification. Now imagine the photo has a low resolution, and if you magnify it, you can only see annoying pixels. If the image had a high resolution, you would be able to see the detail clearly after zooming in. So magnifying is zooming in, while…