Presentation on theme: "Evolutionary origins of plants: algae"— Presentation transcript:
1Evolutionary origins of plants: algae “Algae” is a historical term. It describes a number of groups of organisms that are plant-like in that they contain chloroplasts and carry out photosynthesis but are outside the lineage of plants.“Algae” is a paraphyletic group i.e. does not consist of an ancestor and all of the ancestor’s descendents.
2Algae Algae have a widespread occurrence Aquatic: marine, freshwater Terrestrial: deserts, soils, trees, rocks, etcSome are symbiotice.g. lichen is a symbiotic alliance between a fungus and an alga.e.g. Green Algae (zooxanthellae) live within reef building corals.
3Growth forms of algaeAlgae take on a variety of forms both microscopic and macroscopicUnicellularColoniesFilamentsMulticellular thallus
4Ecological Importance of algae Are very important primary producers especially in marine ecosystems.Play major roles in global cycling of C, N, and O2.Their photosynthetic activity forms the basis of complex communities.These organisms are ecologically important because they are primary producers, taking up CO2 and producing O2 during photosynthesis,They form the basis of complex communities, and contribute to the global cycling of oxygen, carbon and nitrogen.Algae are economically important and we use them for various food sources, (a well known example is sushi), supplements, biochemical and biotechnological applications, in fact one recent application is using green algae to produce biodiesel.Certain species are used as environmental indicators to track temperature fluctuations and nutrient levels, particularly in aquatic systems.** All of these applications and used of algae are reliant on accurate understanding of species and their relationships.***
5Major groups of algae Red algae: Rhodophyceae Brown algae: PhaeophyceaeGreen algae: Chlorophyta
6Rhodophyceae (red algae) Fossil record: BYA~ 5,500 speciesMostly marine, few freshwaterLive attached to surfaces (rocks, shells, other algae)Many are reef-building algae (corallines: CaCO3 accumulates in cell walls)
7Rhodophyceae (red algae) Body forms: Unicellular, simple filaments or complex filamentous aggregationsChlorophyll aCell walls: cellulose, some with CaCO3
8Phaeophyceae (brown algae) Largest and most complex algae.All are multicellular and most are marine.Body form: Thallus (plant-like but lacks true roots, stems and leaves).Thallus includes holdfast, stipe and leaflike blades.Include the largest seaweeds such as the kelps.Cell walls contain cellulose.Chlorophyall a and c.
10Chlorophyta (green algae) Fossil record: BYA~ 8,000 species (500 genera)Marine, freshwater, terrestrial.Attached or planktonic.Chlorophyll a and b.Many species form symbiotic relationships with other organisms.Unicellular, filaments, colonies, also thallus body form.
11Chlorophyta (green algae) Cell walls: absent, cellulose, or modificationsLand plants are derived from green algae.Many taxonomists believe green algae (and red algae) should be included among the Plantae.
12EndosymbiosisSymbiotic organisms are those that have a close mutually dependent relationship with another organism.An endosymbiont is a cell that lives within another cell.The forerunners of modern eukaryotic cells are believed to have been symbiotic associations of prokaryotic cells.
13EndosymbiosisThe role of endosymbiosis in evolution was developed most extensively by Lynn Margulis of the University of Massachusetts.
14EndosymbiosisThe proposed ancestors of mitochondria most likely were aerobic heterotrophic bacteria.
15MitochondriaMitochondria contain own DNA (circular plasmids like bacteria)Likely originated as aerobic bacteria, then engulfed~1.5 Billion Years ago
16ChloroplastsChloroplasts are believed to be descendents of photosynthetic prokaryotes (most likely cyanobacteria) that became endosymbionts within larger cells.About 1.5 mya thus the first “plants” evolved from the engulfing of a photosynthetic prokaryote by an aerobic eukaryote.
18Ploidy Level How many sets of chromosomes? Diploid (2n) - “typical” 2 forms of each gene (alleles)Haploid (1n) - ex. sex cellsSingle copies; product of meiosisPolyploid (4n, 8n, 6n…) - anything more than 2n
19Animals: One animal, one generation Single generation is diploid (2n)Produces short-lived haploid (n) sex cells2n = 46n = ??Paul Decelles
20Plants: One plant, two generations One generation is diploid (2n)Produces n spores that grow into…One generation is haploid (1n)Produces n gametes - later fuse and make a 2n individualPaul Decelles
21Plants: “One plant is always two” One generation is diploid (2n)Produces n sporesOne generation is haploid (1n)Produces 1n gametes - later fuse and make a 2n individualSPOROPHYTE“spore [producing] plant”GAMETOPHYTE“gamete [producing] plant”