The Evolution of Life on Earth Major Episodes in the History of Life Earth was formed about 4.6 billion years ago. (1) Evolved by 3.5 billion years ago (2) Began oxygen production about 2.7 billion years ago Lived alone for almost 2 billion years Continue in great abundance today (1) (2) (3) (4) (5) (3) Single-celled eukaryotes first evolved about 2.1 billion years ago. (4) Multicellular eukaryotes first evolved at least 1.2 billion years ago. (5) Modern humans appeared about 200,000 years ago! : Bacteria & Archaea Collective biomass is at least 10 times that of Eukaryotes Are the simplest organisms living on earth today and the most abundant Mostly unicellular (single-celled), some are colonial organisms Kingdoms 1
live deep within the Earth and in habitats too cold, too hot, too salty, too acidic, or too alkaline for any eukaryote to survive. Deep Sea chimneys (12,000 feet deep) Temperature above 170F! Extremophile Archaea Hot springs Head of a pin Extremophile Archaea Halophiles (Extremely salty Environments) Salt-producing ponds, San Francisco bay, 5-8 times more salty than sea water! Main differences with Eukarya 1) lack nuclei 2) Have cell walls exterior to their plasma membranes 3) Cell size: Much smaller than Eukaryotes: Bacteria <1μm, Eukaryotes >10 μm 4) DNA: No chromosomes in 5) Cell division: Asexual by binary fission in bacteria, variable in Eukaryotes 6) Internal compartmentalization: Lack other membrane-enclosed organelles, only ribosomes 7) Metabolic diversity: Only one type of photosynthesis in Eukaryotes. Several different ways for processing energy in prokaryotes 2
Bacteria Archaea Both bacteria and archaea have: NO nucleus A single loop of DNA: NO chromosomes! Asexual reproduction Reproduction by binary fission. The bacteria we normally know exist Many free-living Some autotrophs Some parasites and cause diseases Some symbionts with eukaryotes These are ancient bacteria which are also prokaryotic but differ from bacteria in that: They have no peptidoglycan on cell walls They are found in extreme environments (hot springs, etc) Why prokaryotes dominate the earth in number and biomass (1)The have an incredibly genetic diversity Two strains of Escherichia Coli are genetically more different than a human and a platypus! Specific ways to recombine DNA without sexual reproduction (2) reproduce quickly by binary fission And can divide every 1 3 hours 20 min in optimal conditions Asexual reproduction Female Sexual reproduction Generation 1 Female Generation 2 Male Generation 3 Generation 4 3
(3)Many prokaryotes form endospores Which can remain viable in harsh conditions for centuries Most endospores can survive in boiling water What prevents a prokaryotic colony to grow indefinitely? Nutrient supply Accumulation of metabolic wastes Predation by other organisms Prokaryotic Nutrition We can group all organisms in four major modes of nutrition based on Energy source (phototroph versus chemotroph) and Carbon source (autotroph versus heterotroph) Plants Algae Cyanobacteria All other Eukaryotes 4
Cyanobacteria: Photoautotrophic bacteria Have different kinds of pigments to trap the sunlight Chlorophyll a Phycocyanin: bluish Phycoerythrin: reddish Pigments help the chlorophyll trapping light that chlorophyll cannot catch and pass the energy to the chlorophyll Bacteria may appear with a different color depending on the amount of these pigments Diversity of Archaea in extreme environments Some Archaea are extremophiles, or lovers of extreme environments Extreme thermophiles prosper in hot environments. The optimum temperatures for most thermophiles are 60 C 80 C 113 C in water near deep-sea hydrothermal vents Extreme halophiles live in such salty places as the Great Salt Lake and the Dead Sea. Methanogens obtain energy by using CO 2 to oxidize H 2, producing methane as a waste product Some species live in swamps and marshes where other microbes have consumed all the oxygen 5
Main Prokaryotic Roles in Marine Ecosystems Nitrogen fixation & Nitrification Nitrogen is needed for proteins and nucleic acids (DNA, RNA) are the only living things that can convert atmospheric N 2 to a form that can be used by other organisms, such as NH 3 (Ammonia) Decomposition Is a chemical recycling and fungi are the main decomposers in marine ecosystems Trichodesmium, also called sea sawdust, is a genus of filamentous cyanobacteria (photosynthetic) that also fix nitrogen. They are found in nutrient poor tropical and subtropical ocean waters 6
Photosynthesis Together with eukaryotic microscopic algae Cyanobacteria (colonial blue-green bacteria) release more than 60% of the O 2 present in out atmosphere Mutualistic symbionts Are very important in the deep sea by producing bioluminescence in specific organs of many deep sea organisms. This in turn is used for Avoiding predators Attracting prey Signaling potential mates Symbiotic Bacteria Serve as Hydrogen "Fuel Cells" for Deep- Sea Mussels by doing chemosynthesis Symbiotic marine bacteria chemically defend crustacean embryos from a pathogenic fungus Symbiotic marine bacteria and marine worm in the deep sea Kingdom Protista What is a protist? Whatever thing that is alive, is a eukaryote, and does not fit inside the other groups! They can be microscopic (protozoa, phytoplankton) or multicellular (more than 180 feet in some seaweeds) 4 Kingdoms of eukaryotes Eukaryotic cells are larger than those of prokaryotes (they typically have 1000 times more volume). Complex organelles are almost always present Kingdoms Sexual reproduction is common and becomes dominant in most groups of plants and animals 7
A tentative phylogeny of protists fungus-like protists plant-like protists All the others are considered animal-like protists Microscopic Protista Most protists are aquatic and free-living Seawater Freshwater Moist terrestrial environments (damp soil or leaf litter) Symbionts: mutualistic or parasites An Ecological classification: Photosynthetic: Plant-like Microscopic Algae PHYTOPLANKTON Ingestive: Animal-like PROTOZOA Always unicellular Not even algae and protozoa can be used as main monophyletic groups (having a common evolutionary ancestor) 8
Photosynthetic: Plant-like Microscopic Algae PHYTOPLANKTON Most algae have a cellulose cell wall. They have chlorophyll inside chloroplasts and carry on photosynthesis. Plankton are small floating organisms Phytoplankton are photosynthetic plankton that forms the basis for most aquatic food chains. Unicellular (Phytoplankton) Others Diatoms Algae Dinoflagellates Multicellular (Seaweeds) Red algae Green algae Brown algae Diatoms the most common eukaryotic producers in marine and freshwater ecosystems With a unique two-part, glass-like wall of hydrated silica Provides protection from predators Can withstand pressure up to 1.4 million kg/m2 24 17 Dinoflagellates (2 nd ) components of both marine and freshwater net phytoplankton More common in tropical waters Shape is reinforced by internal plates of cellulose Two flagella make them spin as they move through the water Flagella Mutualism with coral polyps and others Dinoflagellates photosynthetic output Is food for reef communities A particular type of dinoflagellate called Zooxanthellae provides about 98% of the food a coral polyp needs to survive Corals provide raw materials algae need in order to make photosynthesis Polyp s tentacles with symbionts Dinoflagellates Coral body 9
Red Tides Rapid growth of some dinoflagellates and other unicellular algae (diatoms, cyanobacteria, etc.) Is responsible for causing red tides, which can be toxic to humans Tides appear red because of carotenoids Bioluminescence ATP driven chemical reaction Creates a glow when water is agitated Where dinoflagellates are in great number Noctiluca Red tide Gonyaulax polyedra: Bioluminscent and also risponsable for red tides Ingestive: Animal-like PROTOZOA Are always unicellular! Foraminiferans Have porous & generally multichambered shells called tests Included before in the general group of amoebas Have pseudopodia, extensions that project from the cell surface Pseudopodia extend through the pores in the test The biggest foram several cm in a single-celled organism Forams remains in marine sediments form an extensive fossil record 10
Radiolarians Tests are fused into one delicate piece, which is generally made of silica The pseudopodia of radiolarians, known as axopodia Radiate from the central body axopodia Also useful for fossil records Ooze hundred of meters thick in some places Ciliates Are the most complex of all protozoa Use of cilia to move and feed, which are powered by ATP and the contraction of protein fibers like in muscles Have large macronuclei and small micronuclei Control the everyday functions of the cell Feeding Waste disposal Water balance Function during conjugation, as in bacteria is a sexual process that produces genetic variation marine tintinnids build vase-like cases (loricas) 11