Cell walls can also be found with bacteria and blue green algae, but no chemical likeness of structure and formation with plant cells can be found. It is therefore considered an analogous feature, i.e. a structure with the same function, which did not derive from a common earlier stage. Differentiated cells are marked by a voluminous vacuole . Besides the clearly visible structures like cell nucleus and chloroplasts can a lot of other granular particles be viewed in a light microscope, some of which can be selectively dyed. The majority of these particles has a size that is at or below the power of resolution of a conventional light microscope and their identification was impossible before the use of the electron microscope .
Mitochondria are a typical example.
The organelles may contain inclusions like crystals, fat droplets, starch grains and others, a feature that is found especially in specialized cells. Cells are no static objects. Very often can plasma currents be observed that are caused by organelles, for example chloroplasts and by different granules. Most of these movements have a direction and sometimes it even looks as if single particles would move along rails. It will be shown later that molecular evidence exists that this impression is right.