Major Groups of Fungi

Over 56,000 species of fungi have been identified and there are many more. Over 430 million years ago fungi started invading the land. The major groups of fungi are assigned names on the basis of reproductive structures.

There are three major lineages:

• Zygomycota
• Ascomycota (sac fungi)
• Basidiomycota (club fungi)

In addition, there are the "imperfect" fungi which are those not yet classified because no reproductive structures have ever been found.

Fungi are pathogens of plants, animals, and humans, and spoilers of food supplies. They are used to manufacture substances such as antibiotics and cheeses.

Modes of Nutrition

• Fungi are heterotrophs that utilize organic matter. They cannot carry out photosynthesis.
• Most are saprobes that get their nutrients from nonliving organic matter.
• Some are parasites that thrive on tissues in living hosts.
• All fungi rely on extracellular enzymatic digestion and absorption. They secrete enzymes that digest organic matter into bits cells can absorb
• Fungi are valuable decomposers in the environment.

Fungal Life Cycles

Fungi reproduce both asexually and sexually, producing large numbers of nonmotile spores, made up of one or a few cells. These are either asexual or sexual, or both. They can resist dehydration and remain dormant until environmental conditions favor germination. Spores are dispersed by air currents and other means. In multicelled species, small, dry spores land and germinate to form mycelia. Stalked structures on the mycelia release spores to propagate the line. Fungal classification is based on the type of sexual spores produced.

Types of Sexual Spores:

• Club fungi make basidiospores on the surface of a club-shaped cell (basidium).
• Sac fungi produce ascospores inside a parent cell called an ascus.
• Zygomycete hyphae fuse to produce a thick-walled zygospore .

Most fungi produce a multicellular feeding structure called a mycelium. This food-absorbing part of the fungus is a mesh of branching filaments. Each tubular filament is a hypha with chitinous cell walls. Interconnections and perforations allow cytoplasmic flow necessary for transport to nonabsorptive parts of the body.

The mycelium grows into a food source. Tips of hyphae secrete digestive enzymes that break down organic material into simple forms that can be absorbed by hyphae.

REVIEW: In most true fungi the individual cellular filaments of the body are called
Answer hyphae.