Chapter 31 – Fungi
Overview –
1. A domain whose organisms show wide biodiversity. Estimated at 1.5 million species
with 150,000 identified.
2. Contains species that are the largest – in biomass – organisms on the planet: honey
mushroom in Oregon occupies 2,200 acres below ground and is 2,600 years old.
A. General characteristics
1. Many are important in recycling of nutrients and degradation of organic matter
- Decomposers, but also includes
- Parasites
- Mutualistic symbionts
2. All are heterotrophs
3. Unlike animals, they excrete enzymes (exoenzymes) and digest organic matter
outside which is then absorbed into the cells
4. Figure 31.2: Body plan mainly consists of hyphae – thin filaments used to
increase surface area for adsorption of food, most cells have walls made of chitin
5. Figure 31.4: Some hyphae (haustoria) are used for penetrating tissues of the host
6. Mutualistic fungi have hyphae used to help deliver nutrients to the plant in
exchange for food from the plant – mycorrhizae
B. Sexual and Asexual life cycles
Figure 31.5: Generalized life cycle of fungi – note: plasmogamy and karyogamy
Spores are produced in both sexual and asexual life cycles
Sexual reproduction is important for adaptive radiation
Asexual reproduction happens primarily with molds (Figure 31.6) and yeast
(Figure 31.7)
5. Molds and yeasts that have no known sexual stage of reproduction are called the
Imperfect Fungi
1.
2.
3.
4.
C. Fungal Origin
1. Fungi and animals are more closely related that are fungi and plants.
2. Both fungi and animals probably descended from a flagellated, unicellular protist
– lineages diverged about 1.5 billion years ago
3. Figure 31.8: Earliest fossils of fungi are from 460 million years ago
D. Fungal Diversity (Table 31.1 – Good overview of the five fungal phyla)
1. Figure 31.9: Fungal phylogeny is fairly diverse
2. Chytrids – Present in lakes and soils.
-
Have flagellated spores called zoospores (live in water, so that makes
sense)
- Some are saprobes (decomposers) and others are parasites.
3. Zygomycetes – Includes species of molds, symbionts and parasites
- Common example is the bread mold
- Group is named for the sexually-produced body structure
(zygosporangium) that is resistant to environmental stresses
- Figure 31.12: Life cycle of bread mold – contains all elements of Figure
31.5
- Figure 31.13: Note abilities of Pilobolus and similar fungi
- Figure 31.14: Microsporidia are unicellular parasites of animals and
protests
4. Glomeromycetes – Includes unique endomycorrhizal fungi called arbuscular
mycorrhizae. These are the primary plant symbionts (Figure 31.15)
5. Ascomycetes – Widespread group that produced spores in bodies called asci
(ascus) that are formed in fruiting bodies called ascocarps
- Figure 31.16: Many different types from unicellular to edible morels
- Figure 31.17: Note same as general life cycle in Figure 31.5.
- However, spores are formed in the asci during sexual reproduction, and
- The number of asexual spores is greatly increased by specialized
structures called conidiophores
7. Basidiomycetes – Includes the mushrooms and shelf fungi (Figure 31.18)
- Phylum is named for the club like structure called a basidium (Figure
31.20: Life Cycle)
- The basidium produces basidiospores that are dispersed by the wind
- Figure 31.19: The mycelium will form a basidiocarp (for example, the
common mushroom) when environmental conditions are right
- The basidiocarp contains basidia that will produce sexual spores called
basidiospores
E. Role of Fungi in human welfare and functioning ecosystems
1. Decomposers that recycle nutrients and chemical elements
2. Often from symbiotic relationships with plants and animals
- e.g., mycorrhizae aid plant nutrition (Figure 31.21)
- also can aid in animal nutrition (Figure 31.22)
- lichens were once thought to be single plant species, but are now known to
consist of merged algae and ascomycetes (Figure 31.23 and 24)
3. Many fungi are pathogens (30% of the known species are parasites, primarily on
plants.
- 10 – 50% of fruit harvests are lost to fungi each year
- Figure 31.25: Examples of fungal diseases of plants (ergot killed 40,000
French people in 944 AD.
- Examples include Dutch Elm Disease and the Chestnut blight
4. Fungal infections of humans is referred to as mycosis
-
Examples include ringworm which is a skin mycosis
Also included are many opportunistic fungi. For example, Candida
albicans normally inhabits the human vagina, but will cause yeast
infections if its growth becomes too rapid
- Patients with poorly functioning immune systems, such as AIDS patients,
often have mycosal infections
5. Practical uses of Fungi
- Fungi are used to make cheeses, alcohol and bread
- Fungi are directly eaten as food (mushrooms for example)
- Figure 31.26: Some Fungi produce antibiotics (e.g. penicillin)