How does fungi obtain nourishment

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Spores allow fungi to expand their distribution and colonize new environments. They may be released either outside the body or within a special reproductive sac called a sporangium. Sexual reproduction introduces genetic variation into a population of fungi.

In fungi, sexual reproduction occurs in a variety of ways and often in response to adverse environmental conditions. Although there are many variations in fungal sexual reproduction, all include the following three stages. Finally, meiosis takes place in the gametangia singular, gametangium organs, in which gametes of different mating types are generated. At this stage, spores are disseminated into the environment, and the cycle can start again.

Like animals, fungi are heterotrophs: they use complex organic compounds as a source of carbon, rather than fix carbon dioxide from the atmosphere as do some bacteria and most plants. In addition, like animals, fungi do not fix nitrogen from the atmosphere and must obtain it from their environment.

However, unlike most animals, which ingest food and then digest it internally in specialized organs, fungi perform these steps in the reverse order: digestion precedes ingestion. Thus, digestion occurs outside of the body. In multicellular fungi, first, exoenzymes are transported out of the hyphae, where they process nutrients in the environment. Then, the smaller molecules produced by this external digestion are absorbed through the large surface area of the mycelium. As with animal cells, the polysaccharide of storage is glycogen, rather than starch, as found in plants.

Fungi are mostly decomposers which derive nutrients from dead or decaying organic matter usually plants. Fungal exoenzymes are able to break down insoluble polysaccharides, such as the cellulose and lignin of dead wood, into readily absorbable glucose molecules. Other fungi form special roles, such as mutualisms with plants, where fungi trade water and key nutrients with plants in exchange for plant sugars. In environments poor in nitrogen, some fungi even resort to predation by trapping other small organisms, like nematodes, via constricting rings within their hyphae.

Fungi really do it all! Symbiosis is the ecological interaction between two organisms that live together, however, the definition does not describe the quality of the interaction. When both members of the association benefit, the symbiotic relationship is called mutualistic. Fungi form mutualistic associations with many types of organisms, including cyanobacteria, algae, plants, and animals. Among the examples of fungal-plant mutualism are the endophytes: fungi that live inside tissue without damaging the host plant.

Endophytes release toxins that repel herbivores, or confer resistance to environmental stress factors, such as infection by microorganisms, drought, or heavy metals in soil.

For the most common example, most terrestrial plants form symbiotic relationships with fungi via their roots. The roots of the plant connect with the underground parts of the fungus forming mycorrhizae from the Greek words myco meaning fungus and rhizo meaning root. In a mycorrhizal association, the fungal mycelia use their extensive network of hyphae and large surface area in contact with the soil to channel water and minerals from the soil into the plant.

In exchange, the plant supplies the products of photosynthesis to fuel the metabolism of the fungus. Even some plants, such as orchids, have developed so strong an association with fungi that their seeds generally cannot germinate and grow without a fungal mycorrhiza partner!

Think: If symbiotic fungi are suddenly absent from the soil, what impact do you think this would have on plant growth? With their versatile metabolism, fungi can break down organic matter which would not otherwise be recycled in the ecosystem. Some elements, such as nitrogen and phosphorus, are required in large quantities by biological systems, and yet are not abundant in the environment unless this breakdown takes place.

Even trace elements present in low amounts in many habitats are essential for growth would remain tied up in rotting organic matter if fungi and bacteria did not return them to the environment via their metabolic activity.

Thus, fungi make it possible for other living things to be supplied with the nutrients they need to live. Because of their varied metabolic pathways, fungi can fulfill many important roles. To understand fungi's role in the ecosystem and support biofuels research, scientists supported by DOE's Office of Science are studying how fungi have evolved to decompose wood and other plants.

Fungi face a tough task. Trees' cell walls contain lignin, which holds up trees and helps them resist rotting. Without lignin, California redwoods and Amazonian kapoks wouldn't be able to soar hundreds of feet into the air. Trees' cell walls also include cellulose, a similar compound that is more easily digested but still difficult to break down into simple sugars.

By co-evolving with trees, fungi managed to get around those defenses. Fungi are the only major organism that can break down or significantly modify lignin. They're also much better at breaking down cellulose than most other organisms. In fact, fungi are even better at it than people and the machines we've developed. The bioenergy industry can't yet efficiently and affordably break down lignin, which is needed to transform non-food plants such as poplar trees into biofuels. Most current industrial processes burn the lignin or treat it with expensive and inefficient chemicals.

Learning how fungi break down lignin and cellulose could make these processes more affordable and sustainable. While fungi live almost everywhere on Earth, advances in genetic and protein analysis now allow us to see how these short-order cooks work in their kitchen. Scientists can sample a fungus in the wild and analyze its genetic makeup in the laboratory.

By comparing genes in different types of fungi and how those fungi are evolutionarily related to each other, scientists can trace which genes fungi have gained or lost over time. They can also examine which genes an individual fungus has turned "on" or "off" at any one time.

By identifying a fungus's genes and the proteins it produces, scientists can match up which genes code for which proteins. Just as different chefs use different techniques, fungi have a variety of ways to break down lignin, cellulose, and other parts of wood's cell walls.

Although fungi appeared millions of years earlier, the group of fungi known as white rot was the first type to break down lignin. That group is still a major player, leaving wood flaky and bleached-looking in the forest. To break down lignin, white rot fungi use strong enzymes, proteins that speed up chemical reactions.

These enzymes split many of lignin's chemical bonds, turning it into simple sugars and releasing carbon dioxide into the air. White rot is still better at rending lignin than any other type of fungus. Compared to white rot's powerful effects, the scientific community long thought the group known as brown rot fungi was weak.

That's because brown rot fungi can't fully break down lignin. Recalling his college classes in the s, Barry Goodell, a professor at the University of Massachusetts Amherst said, "Teachers at the time considered them these poor little things that were primitive.

Never underestimate a fungus. Even though brown rot fungi make up only 6 percent of the species that break down wood, they decompose 80 percent of the world's pine and other conifers. As scientists working with JGI in discovered, brown rot wasn't primitive compared to white rot. In fact, brown rot actually evolved from early white rot fungi. As the brown rot species evolved, they actually lost genes that code for lignin-destroying enzymes.

Like good cooks adjusting to a new kitchen, evolution led brown rot fungi to find a better way.