Fungi Kingdom: Characteristics, Reproduction, and Classification
The Fungi Kingdom
The fungi are a large group of organisms; they may be unicellular or multicellular.
Characteristics of Fungi
- They are organisms without chlorophyll.
- They reserve substances as drops of oil.
- They are unicellular or multicellular.
- Most contain a substance called chitin, a nitrogen polysaccharide found in the exoskeleton of arthropods (insects).
- They have a cell wall composed of cellulose.
- They are heterotrophs.
Fungi have a large number of species. Many are saprophytes, feeding on dead remains, helping animals and plants decompose. Many fungi are parasites, living on higher organisms. There are other fungi that live on animals; for example, fungal infections like athlete's foot and ringworm are caused by fungi.
Reproduction of Fungi
Fungi reproduce by spores, which are elongated spherical cells. When conditions are favorable, they germinate, causing a kind of long tube called a "hypha".
Classification of Fungi
Fungi are classified into four main groups:
1. Phycomycetes
These are the simpler fungi. They are linked to aquatic life, reproducing sexually by spores, and some live as parasites or saprophytically. When mature spores reach a favorable environment, they germinate and give rise to a new asexual fungal cycle. Sexual reproduction occurs when two gametes unite to form a zygote, which will give rise to a new fungus. Among these are bread molds.
2. Ascomycetes
These are fungi in which spores develop within the fungus itself. Some are microscopic, and some species are visible to the naked eye. Among ascomycetous fungi are yeast and Penicillium.
3. Basidiomycetes
These fungi are more evolved and are generally known under the name of the mushroom cap. This group includes all edible fungi and some poisonous mushrooms.
4. Deuteromycetes
This is a group of fungi for which sexual reproduction is not known; it is assumed they reproduce only asexually by forming spores. They can be parasites or saprophytes. An example is Candida albicans (candidiasis).
Importance of Fungi
- Some antibiotics are extracted from them.
- Many are used in industry.
- Many act as decomposers of plant and animal remains, returning chemical components to the soil.
Lichens
A lichen is an organism that originates from the association of an alga and a fungus. Usually, it involves a blue-green alga or a fungus associated with an ascomycete (mushroom cap).
Lichens are classified into 3 types:
- Crustose lichens: Those that stick to rocks or trees, forming a hard crust.
- Foliose lichens: Those that are shaped like more or less fleshy plates.
- Fruticose lichens: Those which have a branched thallus.
The association of a fungus with an alga is called mutualism, in which both organisms benefit.
Propagation of Lichens
The propagation of lichens is not entirely clear; it is only known that fungi produce spores that are randomly dispersed and fuse with the algae, causing the lichen to form.