Characteristics of Fungi

Fungi (plural, the singular noun is fungus) are classified within the Biological Fungi Kingdom, so apart from plants, animals, and bacteria.

Why are fungi interesting and important ?

Fungi play key roles in many biological processes, including many processes that support, and in other cases adversely affect, other forms of life. For example, the types of fungi in soil affect the types of plants that thrive there, hence also the animals likely to make their home in that area.

It is useful to know about the characterics of fungi in order to appreciate how fungi differ from plants, animals and bacteria.

The following list also introduces key terminology about fungi (words in bold).

General characteristics of fungi:

• Fungi are eukaryotic, i.e. their cells contain a membrane-bound nucleus and other membrane-bound organelles.
  See prokaryotic vs eukaryotic cells for more about what is meant by 'eukaryotic'.
• Fungi have cell walls* (plants also have cell walls, but animals have no cell walls).
  *A difference between fungi and animals.
• Fungi cell walls are composed mainly of a carbohydrate called chitin*, while plant cell walls are composed mainly of cellulose.
  *A difference between fungi and plants.
• Fungi are achlorophyllous, which means they lack the chlorophyll pigments present in the chloroplasts in plant cells and which are necessary for photosynthesis. Fungi are therefore incapable of photosynthesis.
  *another difference between fungi and plants.
• The (carbohydrate) molecule used to store energy in fungi is glycogen.
  Glycogen is also used to store energy in the muscle and liver cells of animals but plants have a different storage molecule, called starch.
  *another difference between fungi and plants.

• Fungi are heterotrophs, which means that they obtain nutrients by absorption.
  (As also applies to other living things, including plants and animals, fungi need nutrients in order to live, grow and reproduce.)
  Some fungi, called saprobiontic fungi, release enzymes that help to break-down dead organic matter into chemicals that the fungi can then absorb and process as a food source. Other fungi are parasitic, meaning that they obtain nutrients directly from other living things such as trees, or even people e.g. in the case of the fungus responsible for Athlete's Foot.
• Saprobiontic fungi are saprobiontic organisms, also called saprobionts. They digest their food externally and then absorb the products of that 'digestion'. To do this they form very thin threads called hyphae that enable the fungus to feed on organic matter, e.g. dead and decaying bodies of plants and animals. See how saprobiontic organisms feed.

More about hyphae ...

• Hyphae can grow and form a network called a mycelium.
• When a mycelium reaches a certain size (the size depends on the species of the fungus), it begins to form structures called sporangia whose function is to release spores.
• A spore is a unit of asexual reproduction, specifically a reproductive cell surrounded by a thick cell wall that protects the cell from environmental extremes and changes, e.g. in temperature and humidity. Such protection matters because spores are often adapted for dispersal and survival for extended time periods until conditions are favourable for the life-cycle of the fungus to continue. (Note: Gametes are units of sexual reproduction e.g. in many animals and plants, while spores are units of asexual reproduction e.g. in many fungi, algae and some plants.)
• In some fungi, threads merge to form a larger structure called a fruiting body that sometimes consists of a cap and stalk e.g. in the cases of many mushrooms and toadstools - see examples of wild fungi.
  Where present, the cap contains spore-producing stuctures such as gills, pores, folds or sometimes 'teeth-like' structures. So, mushrooms and toadstools are the reproductive, i.e. spore-releasing, parts of fungi.
  See the diagram of the structure of a mushroom for an illustration of the main parts of a fruiting fungus.

Although the above applies to many fungi, not all fungi produce hypae.

Above: Example of yeast growing in agar in a petri dish

• Yeasts are unicellular fungi that do not produce hyphae.
  'Wild' yeasts feed on sugar on the surface of the fruits of fruiting plants and the nectar of flowers. From these 'wild' yeasts people have found and developed certain yeasts for use in the production of human food incl. e.g. for making bread and fermentation to produce alcoholic drinks.
• In general fungi can reproduce both sexually (i.e. using genetic material from seperate male and female partners) and asexually (via formation and release of spores from one individual). Some fungi appear to reproduce only asexually while many fungi can reproduce both sexually and asexually.
  There are fundamental differences between the processes involved in the reproduction of fungi compared with the processes involved in the reproduction of the various types of plants and animals.

Warning: Some fungi, incl. mushrooms and toadstools are highly poisonous so should never be eaten.
Although fungi are interesting to look at and study, it is dangerous to eat or 'taste' wild mushrooms without appropriate expert knowledge.

For more about fungi see a list of wild mushrooms and other fungi (examples of species found in the British Isles).