Bio 20: Diversity of LifeFungi - Teacher Notes

Kingdom Fungi

Major Features

Cell Walls

Unlike plant cells which have cell walls composed of cellulose, fungal cells have cell walls composed of chitin (pronounced KI tun). Chitin is a strong flexible carbohydrate.

Hyphae (pronounced HI fee)

The body of a multicellular fungus is composed of thread-like filaments called hyphae. Hyphae grow at their tips and branch to form a netlike mass called mycelium.

The large surface area of hyphae helps the fungus to obtain nutrients.

In mushrooms, it is difficult to see individual hyphae yet they compose the above ground reproductive structure (called the fruiting body) and the underground mycelium.

Fungi belong to the Domain Eukarya and Kingdom Fungi.

Characteristics Unicellular or

multicellular Eukaryotic Heterotrophic Decomposers

Bio 20: Diversity of LifeFungi - Teacher Notes

Cross-walls

In many fungi, hyphae are divided into cells by cross-walls called septa. The septa have large pores that allow nutrients, cytoplasm, organelles, and even nuclei to flow between cells.

Some fungi are aseptate, meaning they have no septa. In this case, the cytoplasm, nuclei, nutrients and other materials flow freely and very quickly.

Bio 20: Diversity of LifeFungi - Teacher Notes

Nutrition in Fungi

All fungi are heterotrophs, but unlike humans who ingest their food and then digest it, fungi digest their food before they ingest it.

Many fungi produce enzymes that break down organic material, allowing the nutrients to be absorbed through their cell walls.

Fungi can get nutrients by being:

1. Saprophytic – A saprobe is an organism that feeds on dead organisms. These fungi are important decomposers and recycler of nutrients in food webs. (e.g. Bracket fungus live on decaying trees.)

2. Parasitic – These fungi absorb nutrients from the living cells of a host organism and cause harm to the host. (e.g. Athlete’s foot is caused by a group of parasitic fungi called dermatophytes.)

3. Mutualistic – Some fungi live in beneficial relationships with other organisms, such as plants or algae. (e.g. The mycelia of a particular fungus cover the root of a soybean plant. The fungus receives sugar from the host while the mycelia increase water and nutrient uptake for the host plant.)

Reproduction in Fungi

Many fungi can reproduce both asexually and sexually although asexual methods are more common.

Asexual reproduction can occur through mitosis, budding, fragmentation, and spores. Asexual methods result in the production of genetically identical off-spring. Sexual reproduction in fungi occurs when nutrients or water are scarce. It produces genetically different organisms. Sexual reproduction occurs via the production of spores by meiosis.

Asexual Reproduction

Bio 20: Diversity of LifeFungi - Teacher Notes

1. Budding – Unicellular yeast cells reproduce asexually by budding. The daughter cell develops while still attached to the parent cell. The cell membrane pinches off to partially separate the daughter cell from the parent cell.

2. Fragmentation – When the mycelium is physically broken apart (say from an animal digging in the soil), the fragmented hyphae will grow into new mycelia. E.g. dermatophytes that can cause athlete’s foot

3. Spore production

A spore is a reproductive haploid cell with a hard outer coat that develops into a new organism. It does not require the fusion of gametes (sex cells) to produce new individuals.

Hyphae produce sporangia (plural – sporangium, single) (specialized reproductive structures), which in turn produce haploid spores.

These spores are released and carried by air, animals, water, and insects.

When spores land on moist nutrient-rich surfaces, new hyphae form.

Sexual Reproduction

Bio 20: Diversity of LifeFungi - Teacher Notes

Haploid hyphae from two different fungi act as gametes.

There are no male and female fungi, just plus (+) and minus (-) strains.

When the plus and minus hyphae fuse, a zygote is formed (now diploid). The zygote matures and undergoes meiosis to produce new haploid hyphae, which can then germinate to produce new fungus.

Adaptations for Survival

Bio 20: Diversity of LifeFungi - Teacher Notes

VocabularyDiploid – cell with a full number of chromosomes (2n)

Haploid – cell with half the number (n) of chromosomes as a diploid (2n) cell

Gamete – a haploid sex cell that can combine with another haploid sex cell and produce a diploid cell

Meiosis – process in which one diploid (2n) cell produces four haploid (n) cells that are not genetically identical

Mitosis – process in which a cell’s replicated DNA divides and two genetically identical diploid (2n) daughter cells are produced

Zygote – fertilized egg

Classification of Fungi

Read in the text pages 438-440.

Most fungi produce trillions of spores. This ensures that at least a few spores will land in suitable locations and begin to grow.

Spores are lightweight and small so that wind and even the tiniest organisms can transport them.

Spores have a have a strong, waterproof outer wall which allows them to survive in extreme temperature and moisture conditions.

Bio 20: Diversity of LifeFungi - Teacher Notes

The fruiting body of a spore-forming fungus is called a sporophore. Fungi are classified based on the type of sporophore they exhibit.

The four major phyla within Kingdom Fungi are Chytridiomycota, Zygomycota, Ascomycota, and Basiodiomycota.

1. Phylum Chytridiomycota (Chytrids)

Chytrids are unique among fungi because they are aquatic and produce flagellated spores. As such, they used to be classified with protists. However, the presence of chitin in cell walls and recent biochemical evidence have shown that chytrids are more closely related to fungi.

It is likely they are the evolutionary link between fungus-like protists and fungi.

2. Phylum Zygomycota (Common Moulds)

Bio 20: Diversity of LifeFungi - Teacher Notes

Zygomycetes are multicellular and terrestrial. For example - Rhizopus stolonifer, black bread mould that grows on bread and other foods.

Moulds form a type of hyphae called stolons that spread horizontally across the surface of food. Rhizoids, another type of hyphae, penetrate the food and absorb nutrients. Sporangiophores, yet another type of hyphae, push up into the air and form sporangia at their tips.

Zygomycetes reproduce asexually via the release of thousands of haploid spores from sporangia.

In poor environmental conditions zygomycetes can reproduce sexually. A plus (+) hyphae and (-) hyphae come together, forming a gametangium. The haploid gametes from the mating types then fuse together to form a diploid zygote.

The zygote develops a thick wall and becomes a dormant zygospore. When conditions improve the zygospore will germinate and sporangiophores and sporangia will develop.

3. Phylum Ascomycota (Sac Fungi)

Bio 20: Diversity of LifeFungi - Teacher Notes

There are more than 60,000 species of fungi found in this phylum! Although the most well known ascomycete – yeast – is unicellular, most members of this phylum are multicellular. For example – edible morels and truffles.

During asexual reproduction, spores are formed at the tips of hyphae called conidiophores. The spores they generate are called conidia.

During sexual reproduction, the fusion of two mating types occurs within a specialized reproductive structure called an ascocarp. Once the haploid gametes form a diploid zygote, cell division occurs and the new cells develop into spores in the ascus, a saclike structure which gives the phylum its name. Spores produced by an ascus are called ascospores.

4. Phylum Basidiomycota (Club Fungi)

Bio 20: Diversity of LifeFungi - Teacher Notes

Basidiomycetes are multicellular and terrestrial. For example -mushrooms, bracket fungi and puffballs.

Basidiomycetes reproduce sexually by forming a basidiocarp, made up of a stalk and flattened cap. Gills are found on the underside of the cap and are lined with basidia, club shaped hyphae that produce spores. Spores produced by a basidium are called basidiospores.

Deuteromycota (Imperfect Fungi)

This is a diverse group that share only one trait – no sexual reproduction has ever been observed. Because of this, these fungi are referred to as imperfect. Further classification of these species is pending.

Interestingly, the antibiotic Penicillin is produced by a deuteromycote.

Ecology of Fungi

Bio 20: Diversity of LifeFungi - Teacher Notes

Symbiosis is a relationship where 2 different organisms live in close association. This includes commensalism, mutualism, and parasitism.

Mutualism is where both organisms benefit from the association. E.g. lichens and mycorrihizae

Lichens Symbiotic relationship between a fungus

and a photosynthetic green algae Both organisms benefit

o algae makes food through photosynthesis

o fungus supplies moisture, shelter, and anchorage

Grow on rocks, trees, and buildings. Considered to be pioneer species

because the fungus component breaks down rock into soil over a long period of time.

Mycorrhizae Symbiotic relationship between a fungus and plant roots Plants with mycorrhiza are healthier than plants without them. Both organisms benefit

o Fungus absorbs sugars made by plant o Plants absorb more water and minerals with aid of the fungus

Most plants have mycorrhizae on their roots Importance of Fungi

Bio 20: Diversity of LifeFungi - Teacher Notes

Like bacteria, fungi can be both help helpful and harmful.

Helpful

Yeasts are used to make beer & bread Antibiotic penicillin Decomposers & recyclers of nutrients Mushrooms eaten as food Help form many soft cheeses Aspergillus is used to make soy sauce

Harmful

Fungal spores cause allergies Molds, mildew, rusts, & smuts damage

crops Cause diseases (athlete’s foot, ringworm) Poisonous mushrooms Can cause yeast infections

Read in the text pages 440-443.