The Origins of Photosynthesis

1. The Origins of Photosynthesis

2. Life’s Calendar

3. The Tree of Life

4. Larger Cells and Organisms Need More Oxygen

5. A Sense of Life’s Time

6. 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 O2 • PS I only • Bacteriochlorophyll • Green sulfur and purple bacteria • Anaerobic mud: CO2 + 2 H2S --> sugar + 2 S • DO give off O2 • PS I and PS II • Chlorophyll a (plants) • Cyanobacteria • Some Cyanobacteria also able to fix N2; 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

7. Cyanobacteria • Gram negative • Photosynthesize similar to plants • First to introduce oxygen to atmosphere of early Earth • Unicellular or colonial • Many fix N2 - only require water CO2, N2 to grow!!! • Thylakoids • Lichens - symbiotic relationship of cyanobacteria with fungi

9. 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)

11. 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

12. 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

13. Chlorophytes

14. Red Algae

15. Brown Algae

16. 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)

17. Dinoflagellate Endosymbionts are Photosynthesizers

18. Diatom Diversity