Fungus

Fungi belong to a unique biological kingdom known as Fungi.

This group includes diverse organisms like microscopic yeasts, fuzzy molds, and large mushrooms. Fungi are eukaryotic organisms, meaning their cells contain a membrane-bound nucleus. While they might look like plants, they are biologically very different. In fact, fungi are genetically more closely related to animals than to plants. This distinction is important because fungi do not perform photosynthesis. Instead, they are heterotrophs, which means they must consume organic molecules for energy.

To get nutrients, fungi use a fascinating process of external digestion. They secrete digestive enzymes directly into their surrounding environment. These enzymes break down complex organic matter into smaller, dissolved molecules. Once the matter is broken down, the fungus absorbs these nutrients through its cell walls. Unlike plants, which use cellulose for structure, fungal cell walls contain a chitin-glucan complex. Chitin is a tough material also found in the exoskeletons of insects.

This unique chemical makeup helps define the kingdom. Most fungi grow through their bodies rather than moving from place to place. This growth occurs through thread-like structures called hyphae. These hyphae extend from their tips using specialized clusters of vesicles called the Spitzenkörper. Some fungi, like yeasts, remain unicellular and do not form these long threads.

Fungi exhibit incredible diversity in their physical forms and life strategies. They can be single-celled, like the yeast *Saccharomyces cerevisiae*, or multicellular and massive.

Some species are dimorphic, meaning they can switch between a yeast phase and a hyphal phase. Others form complex fruiting bodies, such as the mushrooms we see in forests. There are also specialized structures like rhizomorphs, which act like roots to transport water and nutrients.

These structures allow certain fungi to spread across large areas of soil or wood. Even in extreme environments, fungi find ways to survive. They inhabit everything from deep-sea sediments to high-salt areas and deserts. Some can even endure the intense radiation found in space.

The study of fungi is a scientific field called mycology.

In the past, mycology was considered a branch of botany, or plant science. This was because fungi are mostly immobile and grow in soil like plants. Early taxonomists like Carl Linnaeus, Christiaan Hendrik Persoon, and Elias Magnus Fries classified fungi by their morphology. They looked at physical traits like spore color or microscopic shapes. However, modern science has changed our understanding through molecular phylogenetics. This is the study of evolutionary relationships using DNA analysis. Recent studies in the early 21st century have reshaped the fungal tree of life. The kingdom is now divided into one subkingdom, seven phyla, and ten subphyla.

Fungi play a fundamental role in the health of our planet. They are the principal decomposers in most ecological systems. By breaking down dead organic matter, they drive essential nutrient cycling. One of their most important roles is through mycorrhizal symbiosis. Over 90% of all plants depend on a partnership with fungi to grow. This relationship helps plants take up nutrients and increases their ability to perform photosynthesis. This process also helps increase carbon uptake from the atmosphere, which can help stop climate change.

Without fungi, the exchange of nutrients in the environment would be much less efficient.

Humans interact with fungi in many surprising ways. We use them directly as food, such as truffles and various mushrooms.

Fungi are also essential in food production through fermentation. Yeast is used as a leavening agent to make bread rise. Fungi are also used to produce wine, beer, and soy sauce. Since the 1940s, we have used fungi to create antibiotics to fight infections.

Beyond food and medicine, fungi are used in industry to create enzymes for detergents. They can even act as biological pesticides to control weeds and insect pests.

However, fungi can also cause significant problems. Some species produce mycotoxins, such as alkaloids and polyketides, which are toxic to humans and animals.

Fungi can also be pathogens that cause diseases in crops, such as rice blast disease. These diseases can damage food supplies and local economies. Some fungi can even break down manufactured buildings or become dangerous to humans. Despite their importance, the fungal kingdom is under threat. Pollution, deforestation, and the use of pesticides and fungicides can harm these organisms. We are still discovering much about them, as only about 148,000 of the estimated 2.2 to 3.8 million species have been described.