The Origins of Photosynthesis

Life’s Calendar

The Tree of Life

Larger Cells and Organisms Need More Oxygen

A Sense of Life’s Time

Prokaryotic Nutrition Dependence on oxygen –Obligate anaerobes: die in presence of oxygen –Facultative anaerobes: grow in either presence or absence of oxygen –Aerobic: require constant supply of oxygen Autotrophic –Do NOT give off O 2 PS I only Bacteriochlorophyll Green sulfur and purple bacteria –Anaerobic mud: CO H 2 S --> sugar + 2 S –DO give off O 2 PS I and PS II Chlorophyll a (plants) Cyanobacteria –Some Cyanobacteria also able to fix N 2 ; probably first photoautotrophs of early Earth to release oxygen Heterotrophic –Decomposers (saprotrophs) –often capable of breaking down unusual materials –Symbiotic bacteria Mutualistic, commensalistic, or parasitic Nitrogen-fixing bacteria, Rhizobium

Cyanobacteria Gram negative Photosynthesize similar to plants –First to introduce oxygen to atmosphere of early Earth Unicellular or colonial Many fix N 2 - only require water CO 2, N 2 to grow!!! Thylakoids Lichens - symbiotic relationship of cyanobacteria with fungi

History of Endosymbiosis Mitochondria derived from proteobacterium capable of aerobic metabolism Chloroplasts appear in several distantly related protist clades –Photosynthetic pigments differ –Not all chloroplasts have a pair of membranes Some have three Primary endosymbiosis –All chloroplasts trace their ancestry back to engulfment of a cyanobacterium Chlorophyll a present in all!! One membrane from cyanobacterium, second from host –Gave rise to chloroplasts of green and red algae Red algae chloroplast retains certain pigments of the original cyanobacterial endosymbiont that are absent in green algae Secondary and tertiary endosymbiosis –All other photosynthetic protist lineages –Ancestors took up a unicellular green algae (euglenoids) –Or in tertiary - protist took up another protist that acquired its chloroplast by secondary (dinoflagellates)

Plant-like Protists Pyrrophyta (dinoflagellates) –2 flagella; one wraps around middle of cell –Cell protected by celluose/silica plates –Chlorophylls a and c, carotenoids –Red-tide Chrysophyta (golden-brown algae; diatoms) –Diatoms formally called Bacillariophyta Diatoms have cell wall of silica; major component of phytoplankton –Chlorophyll a and c, fucoxathin Euglenophyta (eugleniods) –1/3 have chloroplasts, rest do not –Chloroplasts like those of green algae Chlorophyll a, b and carotenoid –2 flagella –No cell wall –Eyespot to detect light

Plant-Like Protists Chlorophyta (green algae) –Closest relatives to plants Chlorophyll a, b, carotenoids Store food as starch Walls of cellulose –Lichens: green algae + fungi Rhodophyta (red algae) –Unicellular to multicellular –Chlorophyll a, phycobilins –Food stored as floridian starch Phaeophyta (brown algae) –All multicellular –Chlorophylls a and c, fucoxanthin –Store good as laminarin

Chlorophytes

Red Algae

Brown Algae

Importance of Photoautotrophic Protists Ecological Importance as Primary Producers –Dinoflagellates Marine phytoplankton Endosymbiotic with corals Ride tides and algal blooms –Diatoms Marine phytoplankton Common in fresh water Diatomaceous earth –Chlorophytes (green algae)

Dinoflagellate Endosymbionts are Photosynthesizers

Diatom Diversity