Lecture 5 Notes
The Fungi
| I. Fungi are an ancient group -
perhaps 400 to 800 MYO. About 100,000 species but
many more thought to exist. Fungal characteristics are: A. all fungi have cell walls composed of chitin, same substance in insect cuticles B. have extracellular digestion, i.e., they secrete enzymes and digest food outside of their body, then absorb nutrients C. no photosynthesis - are heterotrophs or saprobes (eat dead organisms) D. fungi do not have flagella on fungal sperm and no centrioles on chromosomes Makes them very different from all other organisms on earth E. Dispersal is via spores - from either sexual or asexual reproduction II. Because of their appearance, were thought closely related to plants, and most introductory botany texts include chapters on fungi A. Recent genetic (DNA) analyses now suggest fungi more closely related to animals B. So, should we move the study of fungi to Departments of Zoology? III. Fungi can be both harmful and beneficial A. Harmful 1. Athlete's foot, yeast infections, wheat rust, loblolly pine stem rust, ergot, bread mold B. Helpful 1. beer production (yeast), cheese production, soy sauce, antibiotic production, 2. fungi important in decomposing organic material, and maintaining functional biogeochemical cycles worldwide IV. Structure A. Most fungi exist as filaments, known as hyphae B. Hyphae subdivided by cross-walls called septa C. A collection of hyphae are known as mycelia. These can extend a great distance For example, one fungus was found to cover an area the size of a football field, with an estimated weight of 40 tons! How did they know it was one fungus? Used DNA fingerprinting D. Major groups of fungi 1. Zygomycetes - ~600 species known a. simplest fungi known - bread mold is in this category 2. Ascomycetes - ~30,000 species known a. reproduce via a structure called an ascocarp, hence the name. Many serious plant diseases in this group, including Dutch Elm Disease, and Chestnut blight b. Yeast are in this group and used for making beer and bread 3. Basidiomycetes - ~25,000 species known a. mushrooms and toadstools in this group, along with stem rusts and smuts b. visible mushroom is reproductive structure - rest of mycelia are belowground, where most of the fungus actually resides c. some very poisonous - Death Angel can destroy your liver and kill you in less than an hour-no antidote - best suggestion - don't ever eat mushrooms in the wild! E. Lichens - special case of symbiotic relationship between algae and fungi 1. Symbiosis discovered by Beatrix Potter - natural historian and illustrator and of course, author of "Peter Rabbit"!! Symbiosis - relationship between two organisms that benefits both 2. Most lichen fungi are ascomycetes. Are a few that are basidiomycetes 3. Fungal cells offer protection against drying for algae symbionts 4. Special hyphae penetrate algae and get carbohydrates 5. Fungi provide nutrients to algae in return 6. Lichens can grow in very inhospitable areas i. on bare rock ii. tree bark iii. hanging from branches as an epiphyte (epiphyte = one organism using the other for support, but not parasitizing it) iv. inside of rock in the Antarctic 7. Some lichens can fix nitrogen from atmosphere 8. Many secrete compounds that can degrade rock and are first step in soil formation 9. Others secrete dyes used in clothing industry 10. No roots so all nutrients derived from rainfall - makes them very sensitive to air pollution and acidic deposition (acid rain). Are excellent bioindicators of air quality F. Mycorrhizae 1. About 80-90% of all plants infected with these type of fungi on their roots 2. Aid in nutrient uptake - especially phosphorus, but also with potassium and nitrogen. Also aids in uptake of water 3. In nutrient poor soils, plants with mycorrhizae fungi often grow better than those without - may have been one of the earliest symbioses because when plants first colonized land, soils were nutrient poor - fungi helped plants get established. In return, they gained carbohydrates 4. Fossils of early land plants shows mycorrhizae were present then |