‘One side will make you grow taller, and the other side will make you grow shorter.’ ‘One side of what? The other side of what?’ thought Alice to herself. ‘Of the mushroom,’ said the Caterpillar, just as if she had asked it aloud.”
Alice’s Adventures in Wonderland, Lewis Carroll
As we move from the Kingdoms of the Archaea and of Bacteria, we leave behind the prokaryotes (the creatures without a nucleus in their cells) to eukaryotes (creatures that have a nucleus in their cells which holds the DNA). Eukaryotic cells are generally quite a bit bigger than the cells of prokaryotes and are more complicated, as we will talk about more later. This divide between prokaryotes and eukaryotes have led scientists to place the kingdoms into three domains: Bacteria, Archaea, and Eukaryotes (protists, fungi, plants, and animals). The vast majority of creatures on Earth are bacteria or archaea, but because eukaryotes tend to be so much bigger, we rival the prokaryotes in terms of mass (the actual size of the creatures).
Among eukaryotes you can find some surprising similarities. For example, animals have melanin in their skin which gives the skin color; some fungi use melanin to produce food in radioactive environments. Similarly, fungi and insects both use a special kind of carbohydrate known as chitin in their bodies, fungi in their cell walls (the stiff outside of their cells) and insects in their exoskeletons (their hard outer coverings). The lack of chitin is one of the main ways that fungus-like protists (like slime molds) are differentiated from true fungi (like actual molds and mildew). Fungus-like protists’ cells are more similar to plants, but they are generally decomposers like fungi.1
We talked about the many different types of mushrooms, but what exactly is a mushroom? A mushroom is actually the fruit of the fungus, like an apple on a tree, so picking a mushroom hurts the fungus no more than picking that apple hurts the tree. The main part of the fungus is actually under the ground, in the log, on the tree, or anywhere else where the mushroom happened to be growing. If you go out in the forest and turn over a log, you might see a bunch of white tendrils all criss-crossing each other. That is the main part of the fungus known as the mycellium (my-see-lee-um). The giant fungus in Oregon that we talked about earlier refers to the area covered by the same mycellium which has many mushrooms that come up at various places. Mycellia (plural of mycellium) do amazing things in the environment, including helping trees talk to each other, as we will discuss more later.
When the conditions are right (such as after it rains or after a forest fire), the mycellia will produce its fruit – the mushroom. Typical mushroom has a tall stalk with a cap on top of it. The caps can be many different shapes, from the typical flat or conical shapes to a v-shape with a deep cleft in the middle. Under the cap, the mushroom might have gills (thin sheets like teeth on a comb), pores (little holes), ridges or teeth that hold the spores (kind of like seeds) of the fungus. As the mushroom ages, it spreads the spores so that more of the fungus can grow. Fungi can also grow by spreading out their mycellia.
Like bacteria, all creatures are either autotrophs (they make their own food) or heterotrophs (they get food from their environment). What about fungi? As we noted, most fungi are decomposers, meaning that they break down dead things in the environment to get their energy, so fungi are heterotrophs.
1It is easiest to talk about the different types of protists in comparison to fungi, plants, and animals, so we will come back to the other two types in later chapters.