Fungi

Fungi are a kingdom of mostly microscopic organisms that are closely related to animals. They include spore producing organisms such as mushrooms, yeast and molds.

Fungi are almost always invisible to the naked eye. At certain times, some fungi will produce large ‘fruiting bodies’ called mushrooms that produce huge numbers of spores for reproduction.

Fungi are different from all other living things by the type of cell wall they have surrounding each of their cells. As opposed to plants, bacteria and some protists which have cell walls made from other compounds (e.g. cellulose), the cell walls of fungi are made from a compound called ‘chitin’.

More than 100,000 species of fungi have been identified by biologists. It is estimated that more than 1.5 million species currently exist on Earth. Two groups of multicellular fungi contain over 95% of all species. One of these two groups is called ‘basidiomycetes’ which includes the mushroom producing fungi.

The study of fungi is known as mycology. Mycology is a very important field of biology because fungi are important for a number of ecological and economic reasons. Consequently, understanding these little organisms is very important to the well-being of humans.

Importance of fungi

Fungi are very important for a number of reasons worldwide. Mushrooms, truffles and yeast have a significant place in the food and alcohol industries as sources of food and in the process of fermentation. They are also used in the production of antibiotics.

Fungi are one of the most important decomposers of dead plant material and the recycling of nutrients back into ecosystems. If nutrients were not recycled, a habitat would become infertile and struggle to support life. On the flip side, all around the world fungi can be problematic for farmers because they can infect and decompose crops.

Many fungi, known as mycorrhizae, live in close association with the roots of plants and actually help them to absorb more nutrients. The vast majority of plants depend on help from fungi to successfully compete with neighbouring plants for nutrients.

Structure of fungi

Fungi live as either single-celled organisms or multicellular organisms. Single-celled fungi are referred to as yeasts. The vast majority of fungi are multicellular.

Most of the body of a fungi is made from a network of long, thin filaments called ‘hyphae’. Hyphae filaments are made from tubular cells that connect end on end. Each cell is surrounded by a cell wall composed of a compound called ‘chitin’. The chitin cell wall is a defining feature of the fungi kingdom.

When the hyphae of a multicellular fungi creates a complex network of filaments it is called a ‘mycelium’. Because the hyphae of fungi are so thin, they have an incredibly high surface area to volume ratio. The large surface area makes fungi extremely well-adapted to absorbing nutrients from soil and other substrates.

Mushrooms

Mushrooms, or toadstools, are the fruiting body common to many species of fungi and are used to store and release spores into the environment. A mushroom is made from a collection of fungal cells called ‘hyphae’. Hyphae are woven together to produce a spore bearing mushroom.

Many species of fungi would be almost completely invisible were it not for their large mushrooms. The rest of their tissue is hidden within the soil or the dead plant that they are feeding on. Mushrooms can be found in most land-based environments but they are particularly common in damp areas where they are most efficient at decomposing.

A mushroom is an example of a basidiocarp, a reproductive structure common to all species of fungi within the division Basidiomycota. The word ‘basidium’ refers to the pedestal-like structures of the fungi within the division. These structures are also responsible for their common name, ‘club fungi’.

The purpose of mushrooms is to bear spores and release them into the environment. Any given mushroom may house and release as many as a billion spores. The spores are then carried by the wind or water and germinate if they land in a nice moist environment with a good food source. This method of dispersal has allowed for single species of fungi to be found all around the globe.

Mushrooms are of huge economic importance especially in Asia and Europe where most of the world’s mushrooms are grown and eaten. They have been harvested and cultivated for centuries for their nutritional value and taste.

The most common market sold mushroom is Agaricus bisporus, or the common white mushroom, which is considered safe to eat (by mushroom standards) but does in fact have toxins which are destroyed during cooking. Many mushrooms can be fatally poisonous and eating wild mushrooms should be avoided unless you have a good knowledge of which mushrooms are safe to eat.

Molds

Molds belong to a group of fungi called zygomycetes. Around 1,000 different zygomycetes species have currently been identified.

Molds are a group of fast growing fungi that are responsible for the spoiling of many foods such as bread, fruits, vegetables and dairy products. The hyphae of molds spread across a food source and penetrate into the food. Once the hyphae have penetrated into the food they are able to absorb it nutrients.

Yeasts

Single-celled fungi are known as yeasts. Around 1,500 species of fungi are recognised as yeasts. Some fungi have the ability to shift between living as yeasts or in a multicellular form with hyphae. Yeasts do not belong to one particular group of fungi but are found in a range of distantly related fungal groups.

Yeasts are found in a variety of places – in both aquatic environments and on land. They are also found living in and on plants and animals.

For thousands of years yeasts have been used to create certain foods. Yeasts are able to metabolize carbohydrates into alcohol and carbon dioxide. Humans have utilised the fermentation of carbohydrates by yeasts to create fermented foods and drinks such as bread, beer and wine.

Lichens

A lichen forms when a fungi and photosynthetic organisms, such as a green algae or cyanobacteria, form a symbiotic relationship. A symbiotic relationship is any relationship between different individuals from different species. In the case of lichens, it is a relationship between a fungi and many single-celled, photosynthetic organisms.

In lichens, photosynthetic cells are caught in a dense network of fungal hyphae. The fungi provides the photosynthetic cells with a suitable habitat. The fungi receives the benefit of excess sugars and nutrients produced by the green algae or cyanobacterium.

Over 16,000 different lichen species have so far been identified.

Mycorrhizae

Mycorrhizae are fungi that live in close association with plant roots and help plants to absorb more nutrients. Mycorrhizal fungi do not come from one particular group of fungi but include species from different and distantly related groups.

The hyphae of mycorrhizal fungi grow into the roots of plants and branch into an extremely thin network of hyphae. These hyphae are far thinner thinner than the thinnest roots of plants and so they are able to absorb more nutrients for their volume.

Over 90% of all plant species have mycorrhizal relationships with a fungal species. If soils are lacking in fungal populations then many plants will struggle to survive in the absence of mycorrhizal fungi.

Last edited: 13 March 2016