The origins of photosynthesis
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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

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The Origins of Photosynthesis

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The origins of photosynthesis

The Origins of Photosynthesis

Life s calendar

Life’s Calendar

The tree of life

The Tree of Life

Larger cells and organisms need more oxygen

Larger Cells and Organisms Need More Oxygen

A sense of life s time

A Sense of Life’s Time

Prokaryotic nutrition

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



  • 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

History of endosymbiosis

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

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 protists1

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



Red algae

Red Algae

Brown algae

Brown Algae

Importance of photoautotrophic protists

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

Dinoflagellate Endosymbionts are Photosynthesizers

Diatom diversity

Diatom Diversity

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