Chapter 9. Fungi and Aquatic Plants Introduction: The Big Step: DIVISION OF LABOUR In single cell organisms (protists) all life functions are performed by specialized organelles within one cell (a.k.a. DIVISION OF LABOUR). Some algae; cyanobacteria (a.k.a. blue-green algae) were also considered part of this group. In multi-cellular organisms individual cells have varying degrees of specialization, beginning with higher algae and fungi. DIVISION OF LABOUR is now carried out by similar groups of cell and organs. The higher algae and fungi are (sort of) considered plants because of this degree of specialization. Evolutionary Significance Fungi and aquatic plants (red, green and brown algae) are thought to have made terrestrial life possible. Most biologists believe that true land pants probably evolved from green algae. It is also believed that the early invasion of land plants was facilitated by symbiotic relationships between fungi and plants via mycorrhizal. That is, the fungi helped supply nutrients to the roots of the land plants in exchange for nutrients. Benefits of a water environment: 1
prevents cells from drying out gives structural support provides nutrients provides medium for fertilization accommodates dispersal of spores Aquatic Plants v. Terrestrial Plants Differences; aquatic plants lack roots, stems and leaves. Similarities all have at least one of four different kinds of chlorophyll (pigment needed to trap sunlight for photosynthesis Fungi v. Plants Similarities eukaryotes with numerous organelles most have cell walls parts of body are often anchored in soil generally stationary lower plants reproduce by spores Differences Fungi not anchored by roots do not photosynthesize*** (most) lack cellulose in their cell wall Higher plants reproduce by seeds. 2
Kingdom Fungi Figure of Mycelium and Hypha Characteristics of fungi cells of fungi are eukaryotic digestion is extra-cellular (outside of the cell), with nutrients being absorbed composed of single strands (hypha, pl. hyphae) into complex masses called mycelium (pl. mycelia) hyphae can be septate (have cross-walls) non-septate (most) hyphae have chitin cell walls heterotrophs reproduction is asexual/sexual/both inhabit dark, warm, moist, high organic locations Life Cycle Figure 3
Fungal diversity Fungi have essentially two parts the visible reproductive structures. These include the sexual gametangia (producing gametes) and asexual sporangia (producing spores) which normally grow on top of the surface. the invisible vegetative structures. This is the larger mycelium mass growing below the surface which busies itself with taking up nutrients to drive the reproduction train. Ecological role of fungi 4
Organic decomposition - waste reduction and nutrient recycling of dead and decaying matter. Breaks down living things into useable nutrients that goes back into the soil to sustain life. Apart from producers, decomposers are probably the next most important life form on the planet. Toxin breakdown - certain fungi can be used to break down harmful pollutants Classification Table 9.1 Fungal Symbionts Two important symbiotic relationships: a. Lichens a symbiotic relationship between algae (green or blue-green) and fungi. The algae provided photosynthetic nutrients (food) to the fungus and the fungus surrounds the algae with carbon dioxide and water (both necessary for photosynthesis). The fungus also provides a support for the organism. The sandwich e.g. reindeer moss, maiden hair/old man s beard Lichens as air-quality monitors. 5
Since lichens absorb water right out of the air, they are more susceptible to air pollution and die if pollution reaches a certain level. b. Mycorrhizae A relationship between plant roots and fungi similar to that of lichens except the fungus does not offer support to the roots. The roots already contain cellulose and therefore are self-supporting. Read p245 Fungal Mimicry Do p245 Review Questions #1,2,3,4 terrestrial adaptations aquatic environment land environment Sporophyte (spore) dominant Gametophyte (gamete) dominant life cycles life cycles WHY? Ecological Role of Algae Unicellular marine and freshwater phytoplankton primary producers in aquatic/marine food webs produce 67% of global oxygen some commercial applications Multicellular marine and freshwater seaweeds 6
chloroplasts plus other pigments, depends on depth. Water filters out different wavelengths of light so chlorophyll comes in different flavours additional pigments also used Reproduction in Algae Alternation of Generations where a species alternates between the diploid spore-producing (sporophyte) method of reproduction and the haploid gameteproducing (gametophyte) Figure 9.10 Life cycle of Chlamydomonas Definitions zygote - the product of fertilization. Occurs when two gametes fuse. Conjugation - the fusion of two gametes. Zygospore - a tough shelled spore that can weather bad conditions before going through meiosis and releasing more spores. 7
Isogamy - when two gametes fuse that are the same size. Heterogamy - when two gametes fuse where one is larger (female) than the other (male) Fragmentation - a form of sexual reproduction where a piece of the parent falls off and starts growing. Introducing The Green Algae unicellular - Clammy the Chlaydomonas. Filamentous - The Rock Band Spirogyra (you think I m kidding, don t you?!) Colonial - Volvo I meant Volvox 8
Multicellular - Ulva Red and Brown Algae. General morphology Fucus p251 Review Questions 8,9,12-15 Kingdom Plantae Characteristics a) Photosynthesis - carbohydrate production using sunlight as an energy source. b) Cellulose cell walls c) Alternation of generations in life cycle d) Sessile (anchored) Plant Diversity 9
Plants can be largely broken into three categories: a) aquatic plants b) non-vascular plants (no xylem or phloem) c) vascular plants (has xylem and phloem) Terrestrial Adaptations Since in the evolutionary scheme of things, terrestrial (land dwelling) plants evolved from aquatic plants certain adaptations would have been necessary. a) A water transport system b) Roots, stem and leaves c) A reproductive system not dependent on the presence of water fro fertilization and spread of new individuals. Evolutionary Trend or Further Evidence of Intelligent Design? A further trend is purported to have happened as well: the trend away from a life cycle dominated by a haploid gametophyte dominated plant to a diploid sporophyte dominated plant*** ***gametophyte - gamete producing structures. In aquatic plants, water-borne gametes were required for fertilization so it makes sense for the plant to be dedicated to that life-style. ***sporophyte - spore producing structures. In terrestrial plants, where water is not the medium in which the plant lives, there is a 10
great need to prevent gametes from drying out. Consequently, a system in which water-requiring gametes are down-played is the best way to go. Refer to Figure 9.6 11