Fungi are a diverse group of eukaryotic organisms, forming their own biological kingdom distinct from plants and animals. This kingdom includes familiar forms such as yeasts, molds, and mushrooms, which are found in nearly every habitat on Earth, predominantly in soil or on plant material. Despite their plant-like appearance in some instances, fungi possess unique characteristics that set them apart, particularly in how they acquire energy.
Fungi and Photosynthesis
Fungi do not perform photosynthesis. This is because they lack chlorophyll, the green pigment essential for capturing sunlight, and chloroplasts, the cellular structures where photosynthesis takes place. Unlike plants that produce their own food, fungi are heterotrophic organisms, meaning they must obtain their nutrition from external sources.
How Fungi Get Energy
Fungi acquire energy by absorbing organic compounds from their surrounding environment. They accomplish this by secreting digestive enzymes outside their bodies onto their food source. These enzymes break down complex organic materials into simpler, soluble molecules, which the fungi then absorb through their cell walls.
Many fungi function as decomposers, also known as saprotrophs, obtaining nutrients from dead and decaying organic matter such as fallen leaves, wood, or animal remains. They play an important role in nutrient cycling by breaking down tough plant materials like cellulose and lignin. This process releases nutrients back into the ecosystem, supporting the growth of other organisms.
Other fungi are parasitic, acquiring energy from living hosts. These fungi can infect plants, animals, and even humans, often causing diseases. They use specialized structures to penetrate host cells and extract necessary nutrients. This interaction can harm the host organism as the fungus consumes its resources.
Fungi also form mutualistic symbiotic relationships with other organisms, where both partners benefit. An example is mycorrhizal fungi, which associate with the roots of most plant species. The fungi extend their thread-like structures, called hyphae, into the soil, increasing the plant’s ability to absorb water and nutrients like phosphorus and nitrogen. In exchange, the plants provide the fungi with carbohydrates, which are the products of their photosynthesis.
Understanding Fungi and Lichens
A common source of confusion regarding fungal energy acquisition comes from lichens. Lichens appear as single organisms but are actually a close symbiotic partnership between a fungus and one or more photosynthetic organisms, typically green algae or cyanobacteria. In this partnership, the photosynthetic partner produces carbohydrates through photosynthesis.
The fungus, known as the mycobiont, provides a protective structure and helps gather moisture and mineral nutrients from the environment. The fungal partner then absorbs the sugars produced by the algae or cyanobacteria. Even within a lichen, the fungus itself does not photosynthesize; it remains heterotrophic and relies on its photosynthetic partner for its energy source. This symbiotic strategy allows lichens to thrive in harsh environments where neither organism could survive alone.