This question comes from a local fifth grader, courtesy of the Science Outreach Program (SOP)’s question box. Teams from the Science Outreach Program make weekly visits to elementary school classrooms in the Portland area to encourage scientific learning in younger students—most importantly, by making it fun. One of the ways they do this is by having a question box, where any student can submit a question they have about the world, and the Science Outreach team will explore the answer with them. Now, this spirit of curiosity has taken on a new form in the Quest. If you have any serious SOP questions, please contact scienceoutreach@reed.edu, but if you just have a silly science question you’ve always wanted answered, we have a Reedie question box in the shape of a turtle outside of Bio 246. Drop us a question!
The short answer to this question is yes. Fungi are alive, and they do have insides. The longer answer is still yes—and here’s why.
All life on Earth falls into one of two categories: prokaryotic or eukaryotic. Prokaryotic organisms, such as bacteria, are unicellular, and do not contain a nucleus or other membrane-bound organelles. On the other hand, eukaryotic organisms are usually multicellular, and these cells contain a nucleus, among other membrane-bound organelles. Fungi are eukaryotic organisms, just like plants, animals, and protists. Until recently, fungi were actually classified as plants, but scientists have realized that this is inaccurate. Plants use the chloroplasts inside of their cells to photosynthesize, and this is how they obtain energy. Fungi do not have chloroplasts and therefore cannot photosynthesize; instead, fungi are more similar to animals in that they are heterotrophic, meaning they must digest other organic material to obtain energy. Additionally, plant cell walls are primarily composed of cellulose, whereas the cell walls of fungi are primarily chitin, a polysaccharide that can also be found in the exoskeletons of different insects and crustaceans such as butterflies, ants, and lobsters.
Fungi make up their own kingdom, of which there are six phyla. Think of a ladder, where kingdom is one rung below domain—prokaryotic or eukaryotic—and phylum is one rung below kingdom. If you climb all the way to the bottom, that’s where you’ll find “species.” The phyla of Fungi all a mouthful: Chytridiomycota, Zygomycota, Ascomycota, Basidiomycota, Glomeromycota, and Deuteromycota.
Chytridiomycota are the “true fungi.” They appeared more than 500 million years ago, around the time of the Cambrian Explosion, a period characterized by the emergence of many of the major phyla that make up modern animal life. Unlike other fungi, the reproductive cells of chrytids have a flagellum which allows them to swim, which is explained by the fact that they mostly inhabit aquatic environments. They are a relic of the time when the world was very different; like crocodiles and sharks, but even older. Some chrytids are parasitic, while others are saprobic, meaning that they survive off of the nutrients from decaying organisms.
Depending on the state of your kitchen, you might already be familiar with Zygomycota. They are terrestrial, as opposed to their chrytid counterparts, and they include Rhizopus stolonifer, the mold that grows on bread, fruit, and vegetables. Like chrytids, some zygomycetes are parasitic—for example, those of the order Demargaritales, which inhabit the intestinal tracts of insects—while others are saprobic. They usually reproduce asexually, but if conditions are unfavorable, they will produce sexually. Sexual reproduction in zygomycetes is referred to as conjugation, which lands them the title of “conjugated fungi.”
You might also be familiar with the phylum Ascomycota, whose name comes from the Greek word askos, meaning “sac” or “wineskin.” Our friends the chrytids also use a Greek root in their name: khutrídion, meaning “little pot.” In both cases, the container word refers to the part of the fungi that holds the spores used for asexual reproduction. Ascomycetes include Ophiostoma ulmi and Cryphonectria parasitica—Dutch elm disease and chestnut blight, respectively—but they also include the Penicillium genus (yay, antibiotics!) and Saccharomyces cerevisiae (yay, common yeast that leavens dough and ferments grain!). There are over 64,000 species in the phylum Ascomycota—as opposed to the 1,050 in Zygomycota—and so there is much variation to be found.
The phylum Basidiomycota comprises around 31,000 species, a little less than half of the amount of species that make up Ascomycota. Basidiomycetes are defined by their basidia, or their reproductive organs. A few species of basidiomycete are referred to as “fairy ring” fungi, because their basidia form rings aboveground while the rest of their body, the mycelium, remains underground. Basidiomycetes reproduce almost exclusively sexually, and they are what most people think of when they are asked to picture a mushroom. During reproduction, basidiomycetes produce basidiocarps, which form the stereotypical mushroom shape. Most edible mushrooms are basidiomycetes, including porcini, chicken of the woods, beefsteak mushrooms, and various kinds of chanterelles. You have probably eaten them—or, if you’re mushroom-averse, at least seen them in the dining hall or the grocery store.
The approximately 230 fungi that make up Glomeromycota have existed for at least 400 million years, but the phylum was only established 25 years ago in 2001. Glomeromycetes are one of the most important groups of organisms on Earth due to the symbiotic relationship they form with trees and plants. They will invade plant root cells and function as a kind of extension to the pre-existing root system. This creates a positive feedback loop of mutual benefit, as the plant is able to uptake more nutrients, and the glomeromycetes are able to receive some of those nutrients, which allows them to grow, reproduce asexually, and further expand the root system. This relationship is vital to nearly every ecosystem on Earth. Some scientists even believe that without glomeromycetes, plants would not have been able to spread across the planet the way that they did millions of years ago.
Last but not least, Deuteromycota: the imperfect fungi. Deuteromycota is a phylum in name only, often describing species that are actually closer to ascomycetes or basidiomycetes. The fungi that ripen Roquefort and Camembert cheese were once classified as deuteromycetes; now, they are members of the phylum Ascomycota. Deuteromycetes are referred to as imperfect fungi because they do not display a sexual phase, instead reproducing asexually through unicellular spores. When breathed in, spores of the genus Aspergillus can cause lung infections, but this will not happen in most people. However, Aspergillus fumigatus, the most common species of fungi of Aspergillus, is developing antibiotic resistance, which will make it harder to treat in the future. Keep an eye out for it when you clean your bathrooms and your basements.
So, not only are fungi alive, but they also have insides, and they have so many different ways of being alive and having insides. This article could only briefly summarize the vast and diverse world of fungi, but if you have any questions, comments, or fungi fun facts that you’d like to share, drop a note in the SOP Question Box outside of the SOP room (Bio 246) or send an email to scienceoutreach@reed.edu.