BIOLOGY 11: UNIT 3: Mycology, Kingdom Fungi

Chapter 9

UNIT 3 OBJECTIVES:1. Examine members of the Kingdom Fungi and describe characteristics that

unify them.

2. Demonstrate sterile technique while preparing cultures.

3. Devise experiments using the scientific method.

4. Demonstrate and evaluate suitability of various growth conditions of fungi.

5. Relate the adaptations of fungi to their diverse roles in ecosystems.

1

UNIT 3: MYCOLOGY: Chapter 9

Fungi: These decomposers are nature's recyclers. Fungi breakdown almost any organic compounds such as: wood, food crops, and plastics. Many fungi benefit humans, yeast is used to make bread, wine, beer; penicillin produces antibiotics, aspergillus flavours pop, and other mushrooms, morels, and truffles supply us with food. Some fungi are parasitic, while others form mutualistic relationships. Fungi were once classified as plants.

Importance Of Fungi & Aquatic Plants:, P.238Fungi & plants have helped to shape the biosphere because their existence led the way for terrestrial organisms.

Aquatic Plants: Aquatic plants had advantages of living in water. It is believed that true land plants evolved from an early ancestor, such as green algae. Successful invasion of plants onto land involved some cooperative arrangement with fungi, such as that in mycorrhizae.

2

Importance of Water: P.2391) Stops Cells From Drying Out, 2) Gives Structural Support, 3) Provides Nutrients, 4) Helps Spore Dispersal & Helps The Meeting Of Sex Cells.

Similar Characteristics of Fungi & Plants:1. Eukaryotic with membrane-bound organelles.2. Most have cell walls.3. Parts of their bodies are anchored in soil. 4. Generally stationary and do not move about.

Different Characteristics of Fungi & Plants:1. Fungi are not anchored in the soil by roots.2. Fungi do not photosynthesize3. Fungi do not contain cellulose in their cell walls.4. However both lower plants & fungi reproduce by spores. Higher plants reproduce by seeds.Kingdom Fungi:, p. 239Fossils resembling fungi date back 900 million years. About 570 million years ago, fungi took a different evolutionary pathway than plants. Their predecessors, like all existing fungi, were heterotrophic.

Characteristics of Fungi: p. 2391) Fungi are eukaryotic cells. All fungi are multicellular, except for unicellular yeast.2) Food is digested externally before being absorbed, fungi are heterotrophs.3) Mycelium : consists of a root-like network of small branching hyphae (filaments) that are

used for food absorption. Each individual filament is called hyphae.4) Cell walls contain chitin, which is a glucose polymer similar to cellulose used by plants.5) Reproduction can be asexual & or sexual. In order to disperse, fungi will create a

reproductive structure specialized for spreading spores by wind. 6) Found in dark, warm, moist places rich in organic matter.

3

General Life Cycle and Reproduction: P.240Fungi reproduce asexually & sexually but always produce spores (Reproductive cells dispersed by air. Spores have a haploid chromosome number - one copy of chromosomes). Spores have thick, resistant coverings to protect them from harsh conditions.

Asexual Reproduction: P. 241Reproduction begins with the formation of spores in sporangia. Spore: is a reproductive cell that carries the haploid number of chromosomes. It has a thick resistant outer covering to protect it. It can be formed by meiosis or mitosis. Spores can germinate into hyphae. Asexual reproduction involves fragmentation (breaking apart) or budding. Fungi reproduce asexually when environmental conditions are favorable. Some unicellular fungi reproduce by mitosis

Most fungi reproduce asexually by spores. Penicillium mold produces

Athlete’s foot fungus reproduce by fragmentation from a small piece of mycelium

Yeast cells reproduce by budding where a part of the cell pinches off to produce more yeast cells.

Sexual Reproduction : , P. 240 1) Haploid stage : involves gametes which are haploid cells from 2 mating strains and

undergo cytoplasmic fusion. Gametes are produced in gametangia (reproductive structures). Nuclei may not immediately fuse after sexual reproduction, but nuclei will divide independently.

2) Dikaryotic stage : cells contain 2 haploid nuclei, derived from separate parents.

3) Diploid stage : nuclear fusion occurs, and forms a zygote with a diploid chromosome number, (2 copies of chromosomes). Diploid stage is short and then the zygote undergoes nuclear division to form new haploid hyphae.

Fig. 9.4 General Life Cycle of Fungus (Sexual Reproduction)

4

The differences in structures, and the sexual life cycles that fungi undergo, separate fungi into divisions (taxonomic category similar to Phylum).

Fungi are Adapted for 2 Main Functions:1) Absorption of nutrients2) Reproduction

Zygospore Fungi (division Zygomycota)Zygospore fungi are both decomposers and parasites. The anatomical structure of the fungus doesn’t change, it just depends on if it is living off of something dead or alive. Rhizopus stolinifer is used as an example in the text to show a typical life cycle of one of these fungi. When the spores of Rhizopus stolinifer land on a piece of bread or fruit, they will grow into full bodies of fungus. This spore could be carried through the air, picked up off of a hand or counter, or it could have come with the bread. Once on the bread, adjacent fungi will grow horizontal hyphae toward each other, and opposite mating types will sexually reproduce by forming gametes, and then they will combine to form a zygote. From the zygote a sporangium will grow and release spores to be picked up by another food source.

5

Sac Fungi (division Ascomycota)In the Middle Ages, it was common for people to have a disease that was known as Dancing Fever. Infected people would be out in the streets, oblivious to their surroundings. At the time, some people attributed this disease to spider bites, but it is now known that it was caused by fungi infected rye bread. When the sac fungi commonly known as ergot, is consumed, it affects the brain and spinal cord, having hallucinogenic effects. It was later discovered, that the active ingredient responsible was LSD. A number of other sac fungi are parasites to plants. Other interesting sac fungi are morels and truffles that are prized delicacies for gourmet chefs, and this part of the fungus is the reproductive structure referred to as the fruiting body. The fruiting body contains many asci, which in turn contain ascospores, which are released to form new fungi in sexual reproduction. As with most fungi the majority of the organism is the vegetative portion composed of mycelium.

Yeast: Yeast cells are also a form of sac fungi. However, they are unicellular. Yeast cells have the ability to respire by fermentation. Because the products of fermentation are CO2 and alcohol, both beer and wine makers use yeast to give the alcohol content, and in the case of beer, the bubbles. Whenever yeast cells are exposed to starch, such as those of fruits and grains, they will ferment the sugar. Yeast is also used in baking, since the CO2 causes the bread to rise. Yeast cells are used to study eukaryotic cells, and yeast was the first eukaryotic organism to have its entire genome mapped. For reproduction, they reproduce asexually only, by either mitosis or budding. Club Fungi (division Basidiomycota)Club fungi include common fungi such as mushrooms that we eat, and shelf fungi that we see growing on trees and logs in the forest. All members of this phylum have fruiting bodies containing basidia, which are a club shaped structure that are the site of zygote formation, and meiosis for spore production. The majority of the life cycle is dikaryotic, meaning there are two haploid nuclei in each cell. They are only diploid for a short time as a zygote, and are haploid monokaryotic from spore formation to germination, where shortly after the cytoplasm of adjacent cells will fuse to form dikaryotic cells. The majority of the structure is vegetative, which is parasitic and saprophytic, and it is found inside the host or matter being consumed. The structure of these fungi that we are familiar with is the fruiting body, which is the reproductive portion of the fungus. The mushrooms we are most familiar with consist of a stalk and a cap. The cap is the portion containing the basidia.

6

Imperfect Fungi (division Deuteromycota)The Imperfect fungi are always capable of reproducing using conidiospores, as did the Sac fungi. These fungi have an unobserved sexual reproduction, making them difficult to classify into one of the other Phyla. Many of these fungi are very well studied, but this stage is unknown because they usually reproduce asexually using conidiospores. One of the most important imperfect fungi is Penicillium this fungus was originally discovered accidentally by Alexander Flemming in 1928. He noticed that a mouldy Petri dish would not grow bacteria around that mold. The development to disease control was done later, but Flemming is usually credited with this discovery.

Other imperfect fungi are used in aging cheeses, and some, such as athlete’s foot and ringworm, cause disease to humans by growing on skin.

Ecological Role of Fungi: To humans, the role of fungi seems destructive, however these roles are essential. Fungi are decomposers and are members of large food chains. They interact with bacteria to transform organic substances into raw materials. Fungi are useful in decomposing harmful pollutants, hazardous chemicals in toxic dumpsites and wastewater treatment plants.

LABORATORY- MOLD GROWTH ON FOODS, p. 243

Fungal relationships: Fungi often benefit from symbiotic relationships with other organisms. Most of the symbiotic relationships discussed already for fungi are parasitic. However many fungi enter mutualistic relationships. Two important symbiotic relationships are: lichens and mycorrhizae.

1. Lichens :Lichen is an example which is sometimes thought of as mutualistic, but it is undetermined whether the algae benefits from the presence of the fungus. This means that it is instead considered to be parasitic. This is because the algae is capable of growing on its own. "Old Man's Beard", "Reindeer Moss", & "British Soldier" are examples of Lichens.

Lichens Consist of Two Organisms: 1) Algae is generally a blue-green or green algae.2) Fungus is a sac fungus.

Role of Algae: share their manufactured food with the fungi.

7

Role of Fungus: fungal mycelium surrounds algae and provides CO2 & H2O for photosynthesis; it also provides support for algae. Reproduction: lichens produce asexually by fragmentation.

Ecological Role of Lichens: Lichens are sources of food for caribou, and other animals. Lichens are found on soil, rocks, & trees and they help form parent soil material. Lichens are valuable in detecting air pollutants because they absorb water directly from the air. They absorb more dissolved toxic substances than do plants. Radioactive fallout from the Chernobyl nuclear power plant disaster was pinpointed by the environmental devastation to lichens.

2. Mycorrhizae :At the roots of most plants, a fungus called mycorrhizae grows and provides the plant with organic nutrients. Even though the fungus feeds off of the plant, the plants which have this fungus infecting its roots grow better than those who don't. Since both organisms are benefiting, this is considered a mutualistic relationship. Some plant seeds will not germinate in the absence of the mycorrhizal fungi. Environmental biologists often monitor mychorrhizal growth in contaminated soils.

Mycorrhizae Consist of Two Organisms: 1) Plant the roots.2) Fungal hyphae of a club fungus.

Role of Plant: provides oxygen and food for the fungus by photosynthesis. Role of Fungus: the fungal mycorrhizae are associated with the roots of trees. Fungal hyphae help the plant absorb nutrients.

8

  

Mycorrhiza is a term that refers to a symbiosis between fungus (myco-) and plant roots (-rrhiza). This symbiotic association is characterized by the movement of carbon from plants to the fungus and in return the fungus facilitates the movement of nutrients to the plants.

<Homework - Review Questions, p. 245 (1-7)>

 

 

 

 

 

 

 

 

 

 

9

 

 

10