A heavy lump of dough
baked in the oven becomes a light, fluffy loaf of bread. A bland chunk of milk
solids become cheese. In each case members of the fungi kingdom are at work.
Fungi do not have root stem or leaves Fungi do not have chlorophyll. Fungi (sing:
Fungus) can live in darkness and also in light. There are more than 100,000
species of fungi. The study of fungi is called mycology. The person who studies
fungi is called mycologist.
Taxonomic Status of Fungi
According to five
kingdom system of classification, ‘Fungi’ is now a separate kingdom. Fungi have
resemblance with plants in (a) having cell wall (b) lack centrioles (c) are
non-motile.
Fungi resemble animals
in having (a) are heterotrophs (b) lack cellulose in their cell wall and
contain chitin so it is thought that fungi and animals arise from common
ancestors. Fungi are different from animals in having (a) cell wall (b) are
absorptive heterotrophs (c) non-motile so fungi are neither plants nor animals.
Fungi have (a) DNA different from all other organisms (b) They show “nuclear
mitosis”. During nuclear mitosis nuclear envelope does not break, instead the
mitotic spindle forms within the nucleus and the nuclear membrane constricts
between the two clusters of daughter chromosomes. In some fungi nuclear
envelope dismantles late.
General Characteristics of Fungi
Habitat:
They occupy a wide range of habitats, aquatic, terrestrial and as parasites on
plants and animals.
Mode
of life: They can be parasites, saprotrophs or mutualists.
Size:
They range in size from the unicellular yeasts to the large toad stool.
Nutrition:
They lack chlorophyll, so they are non-photosynthetic. Thus mode of nutrition
is heterotrophic. Digestion takes place outside the body and nutrients are
absorbed directly.
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| Mycelium |
Cell
walls: Cell walls are rigid containing chitin as fibrillar
material. It has a high tensile strength, gives shape to the hyphae and
prevents osmotic bursting of the cells. Chitin is more resistant to decay than
cellulose and lignin present in the plant cell wall.
Food
storage: If carbohydrate is stored, it is usually as
glycogen and not starch.
Thallus:
The thallus or the body of most fungi is a multicellular structure known as
mycelium. A mycelium (Greek: Mycelium, fungus filaments) is a network of
filaments called hyphae (Greek: hyphae, web). Hyphae give the mycelium quite a
large surface area per volume of cytoplasm, and this facilitates absorption of
nutrients into body of the fungus.
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| Fungal Hyphae |
Hyphae:
The hyphae may be non-Septate (aseptate) or Septate. Non-Septate (L. septum,
wall) hyphae have no cross walls, are multinucleated i.e. they have many nuclei
in the cytoplasm such hyphae are called coenocytic hyphae e.g. Rhizopus.
Septate fungi have cross wall e.g. Penicillium.
Motility:
Fungi are non-motile, lack basal bodies and do not have flagella at any stage
of their life cycle. They move towards a food source by growing towards it.
Reproduction:
A fungus reproduces both asexually and sexually.
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