Lecture 33 April 21 2003. R.Jones Chapter 17
The Kingdoms of Living Organisms- More on Protists and Plants
1. The Fungal Kingdom (Chapter 17) is characterized by organisms that have no motile part of their life cycle, they have chitin in their cell walls and are all heterotrophic.There are three major groups of fungi, the bread molds or zygomycota (also known as zygomycetes), the ascomycota or sac fungi that include the yeasts, and the basidiomycota or toadstools, puffballs, bracket fungi and mushrooms.
2. Zygomycetes are important decomposers as well as causing diseases in plants. Ascomycetes include fungi such as the bread/berewing yeast, Penicillium (from which penicillin is produced), Claviceps purpurea (the ergotism-causing organism). The ergot-producing fungus synthesizes LSD and people ingesting rye grain (or bread made from rye) get ergotism and hallucinate and may die. Morrels and truffles are also ascomycete fungi.
3. Basidiomycetes are the common mushrooms, puffballs, toadstools, bracket fungi etc. They are important as a source of food but they can be highly poisonous and can also produce hallucinogenic compounds as in the case of psilocybin.
4. Lichens are an example of a mutualistic symbiosis between fungi and photosynthetic algae or cyanobacteria. The fungus provides shelter for the photosynthesizer and the photosynthesizer provides the heterotrophic fungus with food. Lichens are important colonizers in extreme conditions, especially in the arctic and antartic.
5. Mycorrhizae are mutualistic associations between fungi and roots of plants. Almost all plants have these fungal associations and they are known to be highly beneficial to the host. Endo- and ectomycorrhizae are found and they differ in the degree of intimacy with which the fungus makes contact with plant tissues. The fungal partner of the mycorrhizal association send hyphae out from the root surface to mine minerals from the soil that are present at low concnetrations such as phosphorus, iron and zinc. In return the fungus gets food from photosynthesis from the host plant.
6. The Plant Kingdom. Almost all photosynthetic eukaryotes (there are some parasitic species) having chlorophylls a and b. Cells store starch and have cellulose in their cell walls. The zygote is protected by tissues, the product being an embryo. Plants are also referred to as embryophytes.
7. Almost all plants live on land although there are aquatic plant species. The evolution of land plants from a green algal ancestor that lived in water required that organs and tissues that can absorb water (roots), transport water, minerals and organic compounds (phloem and xylem), as well as organs that minimize water loss from above ground parts (cuticles and stomates) evolve. Also, because water provides support land plants required supporting tissues and this was in the form of lignified cells. Special means of sexual reproduction also evolved that did not require liquid water for gametes to fertilize.
8. Bryophytes are thought to be similar ot the first plant that evolved and colonized land. Liverworts, hornworts and mosses make up this group of plants. They do not have a clearly differentiated root and shoot system. They lack true leaves and they have no xylem and phloem.
9. The bryophyte body is that of the gamete producing part of the life cycle, called a gametophyte. These gametophytes are haploid (N) plants and make gametes by mitosis! Compare this with gamete production in animals where meiosis produces gametes. The sperm is motile and water is required for fertilization to occur. The resulting diploid (2N) zygote developes into a spore producing structure that is attached to the fgemale gametophyte. Haploid spores are produced by this 2N sprophyte and the haploid spores germinate to give new male and female gametophyte plants. The fact that motile sperm are required for sex in bryophytes makes them relatively poorly adapted to land.