Most microorganisms are unicellular organisms, but they also include organisms of appropriate size with few cells. Such tiny creatures, which are only compared to the rest of the animal and plant kingdom because of their small size, are the subject of microbiology. However, they do not form a uniform group in the system of living beings. Some microorganisms are important for nutrition, others are parasites and pathogens of infectious diseases.
Bacteria are prokaryotes, which means that their DNA is not contained in a nucleus separated from the cytoplasm by a double membrane, as in eukaryotes, but in them, as in all prokaryotes, the DNA lies freely in the cytoplasm, compressed together in a small space, also called nucleoid.
To the Archaea belong
They live in environments with a very high salt concentration. With an optimum temperature > 80 °C, they have a pronounced heat stability. They can still grow at the boiling temperature of the water, but not at less than 60 °C. They are found, for example, in hydrothermal springs and in deep-sea hot water fireplaces.
They come z.
Fungi are eukaryotes and can be found as unicellular organisms like baker’s yeast or as multicellular fungi like mycelia. They reproduce and spread sexually and non-genderly through spores or vegetatively through the spread of mycelia, which can be very long-lived in some cases. Fungi are heterotrophic and usually feed on the fact that they excrete enzymes in the immediate environment and thus digest polymeric, water-insoluble nutrients and absorb them into the cells. The fungi differ from plants in their heterotrophic lifestyle without photosynthesis, and most also in the presence of chitin in the cell wall.
They differ from the animals among other things by the presence of a cell wall. The groups formerly known as “low fungi”, i.e. slime fungi, fungus-like protists such as the egg fungi or hypochytriomycota are no longer counted among the fungi. The scientific discipline dealing with the study of fungi is mycology.
The term alga in the broader sense includes aquatic eukaryotic organisms that carry out photosynthesis but do not belong to the plants. In the narrower sense, this refers to numerous protestist groups. Algae include both microscopically small unicellular and multicellular, sometimes huge, plant-like organisms. By definition, microorganisms are only single to small cell algae, they are called microalgae.
Like all algae, microalgae carry out photosynthesis, they use light as an energy source and are carbon autotrophic. Algae are not a true kinship group in the sense of phylogeny and systematics, but are a paraphyletic group. The scientific discipline dealing with the study of algae is phycology.