Presentation on theme: "Chapter 28~ The Origins of Eukaryotic Diversity. A.For about 2 billion years, eukaryotes consisted of mostly microscopic organisms known by the informal."— Presentation transcript:
Chapter 28~ The Origins of Eukaryotic Diversity
A.For about 2 billion years, eukaryotes consisted of mostly microscopic organisms known by the informal name “protists.” B. Most are aerobic, some are photosynthetic, and some are “mixotrophs” like the euglena. I.Protists: the most diverse of all eukaryotes
C. Modes of nutrition vary: 1. Ingestive (animal-like); protozoa “first animal” 2. Absorptive (fungus-like); slime molds 3. Photosynthetic (plant-like); algae (Amoeba eating a paramecium) D.Motility: 1. Flagella (9+2) 2. Cilia E.Life Cycles and Reproduction 1. Mitosis 2. Asexual 3. Sexual: Syngamy (Paramecium dividing by binary fission)
4.Life Cycle: Spend most of their lifetime in the haploid state. 5.Many protists can form cysts, which are cells that are resistant to harsh conditions. 6.Most of the 60,000 known protists are unicellular, but some are colonial and others multicellular.
F.Habitat: 1. Aquatic/Moist environments a.Plankton: important microscopic protists that drift or swim weakly on the water surface. b.Phytoplankton: algae and prokaryotic cyano- bacteria. Support most marine and freshwater food webs
II.Origin and Diversification of Eukaryotes A.Review: Eukaryotes have membrane bound organelles, nucleus, mitochondria, chloroplast, cytoskeleton, 9+2 flagella, multiple linear DNA, life cycles involve mitosis, meiosis, and sex. B.Theory of Endosymbiosis: Mitochondria and Chloroplast were formerly small prokaryotes living within larger cells.
1.Mitochondria and chloroplasts were undigested prey or parasites 2.Mitochondria evolved before chloroplast (as not all eukaryotes have chloroplast) 3.Evidence for endosymbiosis: a. Endosymbiotic relationship: Example – Paramecium bursaria contain green algae
b.Similarities between bacteria and chloroplasts and mitochondria: -small size -replicate by splitting like binary fission -genome: circular DNA -Mitochondria ribosomes resemble prokaryotic ribosomes C.Ancestors of mitochondria and chloroplasts: 1. Cyanobacteria Chloroplast (photosynthesis) 2. Proteobacteria Mitochondria (SSU-rRNA analysis) D.Algae have various types of plastids. Some algae have chloroplast with 2 membranes, others have 3 or 4 membranes.
Secondary endosymbiosis: explains how and why some protists like algae have various types of chloroplasts.
E. Evolution of the 3 Domains: 1.Analysis of genomes reveal that both archaea and eukaryotes have genes of bacterial origin. 2.Common ancestral community of primitive cells swapped DNA many different times.
F. Phylogeny of Eukaryotes: 1.Based on comparisons of cell struct., life cycles, molecular analysis (SSU-rRNA, amino acid sequence)
III.Protist Systematics & Phylogeny, I A.Diplomonads- groups lacking mitochondria; early eukaryotic link; Giardia (human intestinal parasite; severe diarrhea); Parabasalids- Trichomonas vaginalis (human vaginal infection)
B.Euglenoids- Euglena; single celled mixotrophic flagellate; can use chloroplasts to undergo photosynthesis if light available or live as a heterotroph by absorbing organic nutrients from the environment Kinetoplastids- Trypanosoma (African sleeping sickness; tsetse fly)
C.Alveolata: membrane-bound cavities (alveoli) under cell surfaces; dinoflagellates - phytoplankton, blooms cause red tides, produce toxins 1. Pfiesteria piscicida, is carnivorous, toxin stuns fish 2. Some have mutualistic symbioses with cnidarians 3. Some are bioluminescent attract predators of predators apicomplexans- parasites of animals Plasmodium (malaria)
ciliates- (Paramecium) Most ciliates live as solitary cells in freshwater. Their cilia are associated with a submembrane system of microtubules that may coordinate movement Like other freshwater protists, the hyperosmotic Paramecium expels accumu- lated water from the contractile vacuole.
Ciliates have two types of nuclei, a large macronucleus and usually several tiny micronuclei The sexual shuffling of genes occurs during conjugation, during which micronuclei that have undergone meiosis are exchanged
D.Stamenophila : named for hair-like projections on flagella; include water molds/mildews and heterokont (2 types of flagella) algae Heterotrophich stamenophila- most molds are decomposers and white rusts & mildews are parasites Photosynthetic stamenophila- algae include diatoms, golden, and brown forms
Photosynthetic stramenopile taxa- known as heterokont algae “Hetero” = two different types of flagella The probable ancestor was a red alga. Ex. diatoms, golden algae, and brown algae Diatoms (Bacillariophyta) have unique glasslike walls composed of hydrated silica embedded in an organic matrix.
Golden algae (Chrysophyta), named for the yellow and brown carotene and xanthophyll pigments, are typically biflagellated -Some are mixotrophic -many live w/ freshwater and marine plankton -most are unicellular, some colonial -At high densities, can form resistant cysts that remain viable for decades
Brown algae (Phaeophyta) are the largest and most complex algae. -Most are multicellular -Most are marine -common along temperate coasts in areas of cool water and adequate nutrients -brown or olive color to accessory pigments in the plastids
E.Seaweeds- the largest marine algae, including brown, red, and green A.inhabit intertidal and subtidal zones of coastal waters (characterized by wave forces and exposure to sun and drying conditions at low tide) B.Structure: thallus = body of seaweed a rootlike holdfast a stemlike stipe leaflike photosynthetic blades
Some brown algae have floats to raise the blades toward the surface Giant brown algae (kelps) form forests in deeper water, stipes may be 60 m long Many seaweeds are eaten by coastal people Ex. Laminaria (“kombu” in Japan) & Porphyra (Japanese “nori”) for sushi wraps gelforming substances extracted in commercial operations Algin (brown algae) & agar and carageenan (red algae)- used as thickeners in food lubricants in oil drilling culture media in microbiology
The life cycle of the brown alga Laminaria is an example of alternation of generations. The diploid individual, the sporophyte, produces haploid spores (zoospores) by meiosis. The haploid individual, the gametophyte, produces gametes by mitosis that fuse to form a diploid zygote.
F.Rhodophyta: red algae no flagellated stages phycobilin (red) pigment most common seaweeds in the warm coastal waters of tropical oceans
F.Chlorophyta: green algae -includes charophyceans -chloroplasts -Large size and complexity in chlorophytes has evolved by three different mechanisms: (1) formation of colonies of individual cells (Volvox) (2) the repeated division of nuclei without cytoplasmic division to form multinucleate filaments (Caulerpa) (3) formation of true multicellular forms by cell division and cell differentiation (Ulva)
Most green algae have both sexual and asexual reproductive stages.
G.Rhizopods: amoebas -unicellular with pseudopodia - To move, an amoeba extends a pseudopod, anchors its tip, and then streams more cytoplasm into the pseudopodium Most species are free-living heterotrophs. Some are important parasites.
H.Actinopods: heliozoans, radiolarians “ray foot”= slender pseudopodia (axopodia) The large surface area created by axopodia help them to float and feed Most heliozoans (“sun animals”) live in fresh water -radiolarian refers to several groups of mostly marine actinopods -the siliceous skeleton is fused into one delicate piece
Foraminiferans, or forams, are almost all marine -Most live in sand or attach to rocks or algae -Some are abundant in the plankton -Forams have multichambered, porous shells, consisting of organic materials hardened with calcium carbonate - Fossil forams often used as chronological markers to correlate ages of sedimentary rocks from different parts of the world
I.Mycetozoa: slime molds (not true fungi) “fungus animals” -use pseudopodia (false feet) for locomotion and feeding -plasmodial and cellular slime molds