The inside of the oral cavity is covered with a layer of squamous epithelial cells. These are relatively large, flat cells that are constantly being produced and rejected by the oral mucosa. It is quite easy to examine these cells microscopically.

In the cells of most plants, crystals consisting of calcium oxalate are found which are formed by a process called  biomineralisation. It is thought that these crystals act as a storage reservoir for calcium and also provide for the storage of toxic waste (detoxification). The crystals come in a variety of shapes and some are characteristic of certain plant groups.

Cyanobacteria or blue-green algae are undoubtedly the most important microorganisms that have ever appeared on Earth. Here you can read more about these fascinating microorganisms.