Fungi and protists
In 1928 Alexander Fleming noticed that a mold growing on one of his culture plates at St Mary’s Hospital in London had stopped the bacteria around it.
Fungi: yeasts and molds
Fungi are eukaryotes, so their cells have a nucleus. Some large fungi such as mushrooms look a little like plants, but they are very different: fungi do not photosynthesize, and their cell walls are usually made of chitin rather than cellulose. Microbiologists study two kinds closely. Yeasts are single-celled fungi, with more than 1,000 known species living everywhere from the deep sea to the human navel. Some are useful, such as the yeast that raises bread and ferments drinks; some spoil food; a few cause infections.
Molds are multicellular fungi made of long filaments that grow into colonies you can see, as on an old orange. They live in soil, rotting food and damp corners, and they play a large part in breaking down dead plants and animals, returning their nutrients to the soil. Some molds trigger allergies and some produce toxins called mycotoxins, but molds have also given us medicines.
Fungi also form partnerships. Mycorrhizal fungi wrap around or grow into plant roots and trade minerals for sugar, and lichens are partnerships of a fungus with algae or cyanobacteria. In bread making, the yeast Saccharomyces cerevisiae ferments the sugars in flour and gives off carbon dioxide, the bubbles that make dough rise.
Protists: everything else with a nucleus
Protists are an informal grouping: eukaryotes that are not plants, animals or fungi. That makes them very varied. Algae are protists that photosynthesize, extracting energy from sunlight and releasing oxygen and carbohydrates. Many algae have cellulose-containing walls, but cell coverings vary among groups. Diatoms, a kind of alga with glassy shells, range from 2 to 200 µm; OpenStax shows a photograph of them living in the sea ice of McMurdo Sound in Antarctica. Cyanobacteria are often called algae too, but they are bacteria.
Protozoa are protists that are often called animal-like because many of them move and feed. Some swim with hair-like cilia, some with whip-like flagella, and others push out parts of the cell as pseudopods, “false feet”, and flow forward, as an amoeba does. Some protozoa photosynthesize, others eat organic matter, and some are parasites. Protozoa make up the backbone of many food webs by providing nutrients for other organisms.
| Group | Wall | Food from |
|---|---|---|
| Yeasts (one cell) | Chitin | Absorbing |
| Molds (filaments) | Chitin | Absorbing, decay |
| Algae | Cellulose | Sunlight |
| Protozoa (one cell) | Usually none | Eating |
| Yeast | Single-celled fungus; more than 1,000 known species. |
| Mold | Multicellular fungus made of filaments; a decomposer. |
| Chitin | Tough material in most fungal cell walls. |
| Diatom | Alga with a glassy shell, 2 to 200 µm. |
| Pseudopod | “False foot” used by an amoeba to move and feed. |
| Penicillin | Antibacterial substance from Penicillium; Fleming, 1928. |
- Fungi: eukaryotes with chitin walls, no photosynthesis; yeasts (one cell) and molds (filaments).
- Molds decompose dead matter; Penicillium gave penicillin (Fleming 1928).
- Protists: eukaryotes that are not plants, animals or fungi.
- Algae photosynthesize; protozoa move with cilia, flagella or pseudopods.
- What are most fungal cell walls made of?
- Chitin
- Cellulose
- Peptidoglycan
- Glass
- Which is true of fungi?
- They do not photosynthesize
- They are prokaryotes
- They are a kind of plant
- They have no cell walls
- About how many species of yeast are known, according to OpenStax? (lower bound)
- Where did Fleming notice the effect of penicillin in 1928?
- On a bacterial culture plate at St Mary’s Hospital, London
- In a bakery in Paris
- In a hot spring
- In a field of wheat
- Fleming noticed the mold in 1928; Florey and Chain began their purification work in 1939. How many years apart?
- What important job do molds do in nature?
- Break down dead plants and animals
- Make oxygen by photosynthesis
- Fix nitrogen in root nodules
- Pollinate flowers
- Protists are best described as…
- eukaryotes that are not plants, animals or fungi
- all single-celled organisms
- bacteria with a nucleus
- small plants
- Diatoms range up to how many micrometres?
- An amoeba moves using…
- pseudopods
- cilia
- flagella
- roots
- Cyanobacteria are often called algae, but they are…
- bacteria
- fungi
- protozoa
- plants
Sources for this course (15)
- OpenStax Microbiology 1.1 What Our Ancestors Knew (fermented drink from rice, honey and fruit in Neolithic China by 7000 BC, Saccharomyces cerevisiae in bread, Leeuwenhoek 1675 "animalcules" in rain water, Golden Age of Microbiology 1857 to 1914; openstax.org/books/microbiology/pages/1-1-what-our-ancestors-knew)
- 1.3 Types of Microorganisms (about 100 µm to see with the eye, animal cell about 10 µm, bacteria about 1 µm, viruses about 100 nm, three domains, coccus/bacillus/spirillum, archaea without peptidoglycan and in extreme places such as Morning Glory pool, protists, algae, diatoms 2 to 200 µm, protozoa with cilia, flagella or pseudopods, fungi with chitin walls, more than 1000 yeast species, molds and penicillin, helminths, prions about one-tenth of a virus; .../1-3-types-of-microorganisms)
- 3.1 Spontaneous Generation (Aristotle, van Helmont's mice recipe of 3 weeks, Redi 1668 with six jars, Needham 1745, Spallanzani, Pasteur 1858 gun-cotton filter, swan-neck flasks, Alhumbert Prize 1862, 1864 lecture; .../3-1-spontaneous-generation)
- 3.2 Foundations of Modern Cell Theory (Semmelweis 1847, 10 to 20 percent vs 1 percent, chlorinated lime; Snow; Pasteur 1856 fermentation; Lister 1867 carbolic acid; Koch's postulates; .../3-2-foundations-of-modern-cell-theory)
- 6.1 Viruses (acellular, obligate intracellular parasites, DNA or RNA never both, capsid, envelope, spikes, helical/polyhedral/complex, 20 nm to 900 nm, Ivanovski 1892 with the Chamberland filter of 1884, pore 0.1 µm, Beijerinck 1898 and virus = poison, Stanley 1935, host range, bacteriophages, FDA 2006 phage spray on lunch meats; .../6-1-viruses)
- 9.1 How Microbes Grow (binary fission, FtsZ Z ring, generation time, E. coli 20 minutes, human generation 25 years, M. tuberculosis 15 to 20 hours, M. leprae 14 days, 2^48 = 281,474,976,710,656 after 24 h at 30 minutes, Nn = N0 2^n, lag/log/stationary/death, budding, fragmentation, Epulopiscium; .../9-1-how-microbes-grow)
- Royal Society: Philosophical Transactions 12:821-831, published 25 March 1677, Leeuwenhoek's Dutch letter of 9 October 1676 "concerning little animals" (doi.org/10.1098/rstl.1677.0003)
- Royal Society archive EL/L1/22 (letter to Oldenburg dated at Delft, 18 pages, partial translation by Oldenburg)
- Royal Society blog "Celebrating Leeuwenhoek", 2023 (first letter via de Graaf, Phil. Trans. 19 May 1673; 190 letters in fifty years; died 26 August 1723 aged 90)
- N. Lane 2015, Phil. Trans. R. Soc. B 370:20140344 (upwards of 1,000,000 creatures in a drop of pepper-water; letter read aloud over several sessions)
- Lens on Leeuwenhoek, letter L-040 (Oldenburg printed less than half; Hooke succeeded later in 1677)
- CDC MMWR 53(34):783, 2004, 150th Anniversary of John Snow and the Pump Handle (31 August 1854, handle removed 8 September 1854, Vibrio cholerae isolated 1883; cdc.gov/mmwr/preview/mmwrhtml/mm5334a1.htm)
- CDC History of Smallpox and Smallpox timeline (Jenner 1796; 33rd World Health Assembly declared the world free of smallpox on 8 May 1980; cdc.gov/smallpox/about/history.html)
- American Chemical Society, Discovery and Development of Penicillin landmark (Fleming 1928 at St Mary's Hospital London, paper June 1929, Florey and Chain at Oxford from 1939; acs.org/education/whatischemistry/landmarks/flemingpenicillin.html)
- Fleming 1929, Br J Exp Pathol 10:226. Sender, Fuchs and Milo 2016, PLoS Biol 14:e1002533 (3.8 × 10^13 bacteria and 3.0 × 10^13 human cells in a 70 kg reference man, ratio about 1.3, bacteria about 0.2 kg).
Checked: 2026-10-17