Fungi are neither plants nor animals. Even so, they are among the most widespread organisms on land. They grow in forest soil, on rotting wood, inside living plants, and in places as harsh as deserts and polar tundra.
Their success rests on a few adaptations. They absorb food instead of eating it. They spread using spores built to travel and to wait. They form partnerships with other organisms. And they can harden into a resting state when conditions turn against them.
Feeding by Absorption
The Mycelium and the Hyphae
Fungi cannot make their own food. They take carbon from other organisms, as animals do. But they do not swallow food and digest it inside the body. They digest it outside and absorb the result.
The feeding structure is the mycelium. It is a branching network of fine threads called hyphae. Each hypha is a narrow tube, and a mycelium threads through soil, wood or living tissue.
Fungi release digestive enzymes from the tips of the hyphae. The enzymes break large molecules such as cellulose and proteins into smaller ones. Those smaller compounds are then absorbed through the hyphal wall.
The shape is what makes this efficient. Thin, densely branched hyphae give the mycelium a high surface area for its volume. A fungus can draw nutrients from a large volume of material while investing little in bulk.
 |
| Hyphae branch into a mycelium, which gives the fungus a very large surface for its size. Image: Ajay Kumar Chaurasiya, CC BY-SA 4.0, via Wikimedia Commons |
Three Ways to Get Food
- Saprotrophs (decomposers): absorb soluble compounds from dead plant and animal matter, and are the main decomposers in forests.
- Parasites: live on or inside a living host and break down its tissue, often causing disease.
- Mutualists: live with another organism in a partnership that helps both sides.
Reproducing Without Water
Reproducing on land raises two problems. Offspring must reach new places without swimming, and they must survive drying out. Fungi answer both with spores.
Spores Built to Travel and Wait
Spores are microscopic and light. Many fungi produce them in enormous numbers. Wind, water or animals then carry them long distances. A tough wall lets a spore wait until conditions improve.
Some fungi also spread by fragmentation. A piece of mycelium breaks away and grows on as a new individual.
Fruiting Bodies
Many fungi also reproduce sexually. Hyphae from two compatible individuals fuse. The result grows into a fruiting body. The familiar mushroom is one kind, called a basidiocarp. The cup- and flask-shaped ascocarp of the sac fungi is another.
A fruiting body protects the developing spores and helps release them. Sexual reproduction also mixes genes from two parents, so the offspring differ from either one. That variation helps a population adapt when conditions change.
 |
| Spores are single cells with a tough wall, built to travel and to wait. Image: Dartmouth Electron Microscope Facility, public domain, via Wikimedia Commons |
Living in Partnership
Many fungi live in long-term partnerships with other organisms. Two of them matter enormously on land.
Mycorrhizae: Fungi and Plant Roots
A mycorrhiza is a partnership between a fungus and a plant root. The hyphae spread through the soil and reach water and minerals the roots cannot. In return the plant supplies sugars made by photosynthesis.
Both partners gain. The fungus gets a steady energy supply and a sheltered place to grow. The plant gets water and nutrients, especially phosphorus and nitrogen, and often more resistance to drought and disease.
Mycorrhizae are the rule rather than the exception. Most land plants form them, including most trees, shrubs and crops. Arbuscular mycorrhizal fungi alone partner with about 80 percent of plant species.
 |
| Inside a root, the fungus trades minerals for sugars. Image: Msturmel, public domain, via Wikimedia Commons |
Lichens: Fungi and Algae
A lichen is not one organism. It is a stable partnership between a fungus and an alga or a cyanobacterium. The photosynthetic partner, the photobiont, makes sugars from light. The fungus cannot photosynthesize, so it takes some of that sugar, and in return it gives structure, protection and moisture.
A lichen is more than the sum of its parts. It builds tissues that neither partner makes alone. It can also colonize bare rock, where neither could survive on its own. Lichens grow almost everywhere on land, from polar regions to deserts.
 |
| A lichen is a fungus and a photobiont living as one body. Image: Norbert Nagel, CC BY-SA 3.0, via Wikimedia Commons |
Waiting Out Hard Times
Fungi face drought, temperature extremes and long stretches with little food. Several adaptations let them wait these out.
Sclerotia
Some fungi pack their hyphae into compact, hardened masses called sclerotia. A sclerotium has a tough outer rind and a store of food inside. It can stay dormant for a long time through freezing and drying. When conditions improve, it germinates and the fungus grows again. Plant pathogens such as Sclerotinia sclerotiorum survive between crops this way.
Thick-Walled Spores
Many fungi make spores with thickened walls. Chlamydospores are the clearest example. The extra wall protects the cell contents until germination is safe.
Extreme Habitats
Fungi live in hot and cold deserts, in polar soils and permafrost, and in acid mine drainage. They are not rare in these places. They are now recognized as key members of those extreme ecosystems.
Why Fungi Matter
These adaptations do more than keep fungi alive. As decomposers, fungi release nutrients locked in dead tissue. As mycorrhizal partners, they underpin plant growth. As lichens, they colonize bare ground and help break it into soil. Nutrient cycling, soil formation and plant health all depend on them.
Key Terms in Plain English
| Term | What it means here |
| Fungi | A kingdom of organisms that feed by absorption and have chitin in their cell walls. |
| Heterotroph | An organism that cannot make its own food and must take carbon from others. |
| Mycelium | The branching network of hyphae that forms the main body of a fungus. |
| Hypha | One fine thread of a fungus; a mycelium is a mass of them. |
| Saprotroph | A fungus that feeds on dead and decaying matter. |
| Parasite | An organism that lives on or in a host and harms it. |
| Mutualist | A partner in a relationship that benefits both organisms. |
| Spore | A single reproductive cell with a tough wall, built to travel and to wait. |
| Fruiting body | The spore-producing structure, such as a mushroom. |
| Mycorrhiza | A partnership between a fungus and a plant root. |
| Lichen | A stable partnership between a fungus and an alga or cyanobacterium. |
| Photobiont | The light-using partner in a lichen, an alga or cyanobacterium. |
| Sclerotium | A hardened mass of hyphae that lets a fungus wait out hard conditions. |
| Chlamydospore | A resting spore with a thickened wall. |
Key Takeaways
- Fungi are not plants; they cannot photosynthesize and must take carbon from other organisms.
- They feed by absorption: hyphae release enzymes and absorb the molecules that result.
- Spores are built to travel and to wait, which lets fungi spread across dry land.
- Mycorrhizae pair a fungus with plant roots, and about 80 percent of plant species take part.
- A lichen is a partnership between a fungus and an alga or cyanobacterium.
- Sclerotia and thick-walled spores carry fungi through drought, cold and famine.
- Fungi recycle nutrients, build soil and support the health of plants.
Frequently Asked Questions
Are fungi plants?
No. Plants photosynthesize and fungi cannot. Fungi also build their cell walls from chitin rather than cellulose, and they feed by absorption instead of taking food into a body cavity.
Is a mushroom the whole fungus?
No. A mushroom is only the fruiting body, the part that makes and releases spores. The main body is the mycelium, a network of hyphae that grows through soil or wood and is usually hidden.
Do fungi need water to reproduce?
They need moisture in order to grow, but their spores do not swim. Spores are carried by wind, water or animals, which is how fungi spread across dry land.
What is the difference between a spore and a seed?
A seed holds a plant embryo with a store of food. A spore is a single cell with a tough wall, and most spores are far smaller. Fungi spread by spores rather than by seeds.
Key references
• CK-12 / LibreTexts Biology: How fungi eat
• Rutgers NJAES FS1384: Mycorrhizal fungi and plant health
• USDA Forest Service: Mycorrhizae
• Australian National Botanic Gardens: What is a lichen?
• Australian National Botanic Gardens: Fungi, dispersal and spore release
• Molecular Plant Pathology: the schizotrophic lifestyle of Sclerotinia sclerotiorum
• Fungi are key players in extreme ecosystems (2022)
Images: Wikimedia Commons, with the author and license named in each caption. This article is general science education.
No comments:
Post a Comment