BIOEE 1780 Lecture Notes - Lecture 11: Great Oxygenation Event, Banded Iron Formation, Photosynthetic Pigment
28 Apr 2018
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Lecture 11 – Algae and the Origin of Land Plants
Plants refers solely to land plants, not the entire Plantae group.
• The earliest Plantae species were aquatic.
• Synapomorphy of plants is having chloroplasts.
o Chloroplasts were obtained by primary endosymbiosis of cyanobacteria.
• Algae: aquatic photosynthetic eukaryotes
o Not closely related
• Major Events in Plant Evolution
Early Proterozoic contained the Great Oxidation Event
• Banded iron formations indicate past oxygen levels
• Cyanobacteria, because they possessed Chlorophyll a, began releasing oxygen ~3 billion years
ago as a product of photosynthesis.
o Plants emerged in the Late Proterozoic.
o Land plants emerged in the Late Silurian.
The ancestor of Plantae was unicellular and similar to glaucophytes.
• Glaucophytes: microscopic freshwater/marine algae
o Sister group of Plantae
o Chloroplasts contain peptidoglycan between their inner and outer membranes
• Also found in cyanobacteria
• Evidence that chloroplasts were cyanobacteria
• Only seen in glaucophytes, not other plant taxa
o Unicellular (no alternation of generations)
o No sexual reproduction → reproduce asexually
Red Algae: marine; most are multicellular
• Red color results from phycoerythrin, an accessory photosynthetic pigment that is found in their
chloroplasts
o Allows them to live in low light conditions
• Contain chlorophyll a
• Can live in salt or freshwater, at varying depths
o Those near the surface contain a higher concentration of chlorophyll a and appear green.
o Those living in deep water accumulate large amounts of phycoerythrin and appear red.
• Sperm are not flagellated and require water to move.
Green Plants: both of their photosynthetic pigments are green
• Synapomorphy: chlorophyll b and starch storage
• Chlorophyll b increases the spectra for photosynthesis, allowing more light to be fixed during
photosynthesis
• Contain chlorophyll a and chlorophyll b
• Store extra photosynthetic products as starch in chloroplasts
• Chlorophytes: the sister group of all other green plants
o Have chlorophyll a and chlorophyll b
o Unicellular and multicellular
o Belong to a clade with the synapomorphy of having chlorophyll b
o Part of a group known as green algae
• Green algae = paraphyletic clade
o Part of the symbiotic relationship that forms lichen (algae + fungus)
Document Summary
Lecture 11 algae and the origin of land plants. Plants refers solely to land plants, not the entire plantae group. Synapomorphy of plants is having chloroplasts: chloroplasts were obtained by primary endosymbiosis of cyanobacteria, algae: aquatic photosynthetic eukaryotes, not closely related, major events in plant evolution. Sperm are not flagellated and require water to move. Green plants: both of their photosynthetic pigments are green. Synapomorphy: chlorophyll b and starch storage: chlorophyll b increases the spectra for photosynthesis, allowing more light to be fixed during photosynthesis, contain chlorophyll a and chlorophyll b, chlorophytes: the sister group of all other green plants. Some algae (outside of this subset) can perform alternation of generations. In some algae, the diploid stage is confined to the unicellular zygote, which produces spores via meiosis: doesn"t qualify as alternation of generations. Green algae: paraphyletic group: unicellular and multicellular, some multicellular algae can do alternation of generations. The egg is retained in the parent: many form symbiotic relationships.
