General Biology/Classification of Living Things/Eukaryotes/Fungi

Introduction

Although you may not recognise fungi, they are just as prevalent as plants and animals. Their spores are in the air which we breathe, fungi allow us to make bread, and mushrooms (a type of fungi) are eaten by us. A few types of fungi are unicellular. For example, yeasts live as individual oval or cylindrical cells. However, the majority of fungi are multicellular. Their bodies are composed of hyphae, a network of fine filaments. In a mushroom, the hyphae are densely packed so it is difficult to see the individual structures when a mushroom is eaten. However, a mushroom is only a specialised reproductive part of the whole fungus. The main part of the fungi is underground in a whole web of hyphae, called a mycelium.

In the mycelium, each fungal cell is separated from each other by a septum. Each fungal cell may have one or more nuclei and remains connected to the mycelium because the septa are porous, allowing cytoplasm to flow through the hyphae and fungal cell walls, made of a hard material called chitin. Some fungi do not have septa, and they appear to be large, branching, multinucleate cells.

Nutrition

Fungi are saprophytes. When they find a source of food (e.g. dead wood, orange peel) , they decompose it and digest it. The enzymes break down larger organic molecules in the substrate into smaller molecules. These smaller molecules diffuse into the fungus, where they are used to allow growth and repair.

Fungi which feed on living cells are parasitic. For example, athlete's foot grows on the human foot. These kinds of fungi produce hyphae called haustoria, which can penetrate host cells without immediately killing them.

However, they are friendlier species of fungi. Many fungi live symbiotically with plants or animals. For example, most trees have fungi living in close contact with their roots. In this relationship, known as a mycorrhiza, there are many benefits:

• Growing around the plant roots and often entering plant cells, the hyphae absorb minerals from the soil and release them in the roots. The fungi gets its source of food (organic nutrients) while delivering food to the plant.

• The mycelium here would increase the surface area, thus the absorptive surface, of the plant roots.

• The fungal cells help to maintain air and water flow in the soil around the roots.

• The fungi may prevent other potentially pathogenic fungi to attack the tree.

Fungal Reproduction

Fungi can reproduce in two ways. Firstly, they may asexually produce through fragmentation. This occurs when pieces of hyphae are broken off, which then grow into new mycelia.

The second method is by spores. Spores are lightweight structures and windblown designed to be transported over long distances and by many mediums, such as on the bodies of insects and birds. They are additionally light enough to be blown away for hundreds of kilometers. Spores may be asexual and sexual. Their sexual properties can be analysed to classify the four phylla of fungi.