Bacteria play a very important part in nature as well as for man. The circa 5,000 species are divided into three large groups: heterotrophs, autotrophs, and mixotrophs. Heterotrophic bacteria enable the circuit of substances between the three kingdoms: mineral, vegetal, and animal. These determine the fixation of free nitrogen from the atmosphere, they participate in fermentations, soil formation, etc. Chemoautotrophic bacteria participate in the formation of sulfur and iron deposits.
Algae are present worldwide in a number of 6,000 species, with dimensions starting from microscopic ones up until a few hundred meters (the algae forming the Sargasso Sea). In the Botanical Museum, inside the three cases, there are displayed samples of all four types of algae: blue, green, brown, and red.
The fungi exhibited in this part of the Museum are inedible and poisonous. There are also displayed some phytopathogenic fungi and their main effects on the different vegetal organs as well as some epixilous fungi (that grow on trees). Merulius lacrymans, the house sponge, is very harmful, it destroys paper and construction wood, frequently causing significant damage in archives or museums. It is exhibited in the Museum, in a special case.
Lichens can be seen in case no. 37. Of the circa 17,000 species of saxicolous, corticolous, and terricolous lichens known worldwide, approximately 10% can be found in Romania. They are the first colonizers of empty and unfriendly substrates, thus contributing to their preparation for colonization with other species. Turnsole is fabricated from lichens like Rocella tinctoria; Evernia prunastri is used in the perfume industry; the reindeer lichen (Cladonia rangiferina) is an important food source for reindeer during the entire winter time.
Moss (bryophytes) are represented in the Museum by 50 species (only original material). Worldwide there are circa 20,000 species of moss, Romania's flora including circa 200 species. They are exposed within the Museum in case 38.
Ferns (pteridophyta) account for approximately 12,000 species, of which 70 are present also in Romania's spontaneous flora. In case 39 there is exposed also authentic material, with species from Romania's flora as well as of the exotic one.
Ferns can be used for multiple purposes: food, medicines (diuretics, combating of intestinal parasites, strengthening of the immune system, etc.), industrial (polishing of metal objects, tawing), etc.
Of the arborescent ferns, whose number has been considerably reduced along the years, so that today it is an endangered species, having contributed to the formation of the oldest coal deposits worldwide, the Museum holds a trunk of the fern Dicksonia antarctica, brought in 1911 from the Tasmanian Island.
Coniferae (gymnospermae) are exhibited in cases 40-44. The collection contains pressed material, cones and seeds of gymnospermae from Romania or other continents: Pinus cembra, Taxus baccata, Araucaria imbricata, Torreja, Ginkgo biloba, Ephedra distachya, E. villarsi.
Coniferae have a multitude of uses: food (seeds of Pinus, Ginkgo biloba, the arillus of Taxus seeds), medicines (ephedrine extracted from Ephedra, the juniper – diuretic and antirheumatic properties), the wood is used for manufacturing furniture and shingle; spruce wood is used for fabricating keyboards, etc.
An old, rare and interesting gymnosperm is Welwitschia mirabilis growing in the Namibian Desert of Southwest Africa as a reminiscence of the flora of 100 million years ago. The trunk has only 2 leaves throughout the plant's whole life, and their length can reach up to a few meters, being torn by the powerful winds that blow in that region. On the superior part of the trunk there are either male or female flowers, depending on the gender of the plant (in conclusion, it is a dioecious unisexual plant). Given the fact that the number of samples of Welwitschia has diminished considerably, it is actually being protected worldwide by the international laws of biodiversity preservation.
Angiosperms, the most developed plants and, at the same time, the most numerous ones, circa 250,000 species worldwide, of which approximately 3,500 are present also in Romania's flora, are displayed in the Museum inside the rest of the cases (45-77) as pressed or conserved material (leaves, flowers, fruit, seeds) of monocotyledon and dicotyledon species of Romania's flora and the exotic one.