Algae

a group of organisms (not a clade) that all derived chloroplasts from the same endosymbiotic event but are now very varied Almost all aquatic

-Algae are named by colour -A range of pigments means more wavelengths can be used for photosynthesis -What pigments an algae has determines its ecological niche and what colour it is

Colour is produced when chlorophyl a absorbs light - absorbs blue and red light best and reflects green light Chlorophyl b and c differ in the wavelengths of light they absorb but all reflect green Chlorophyl produces green colour associated with plants

Carotene and Xanthin - absorb blue and green and so appear yellow/red/orange Phycoerythrin and phycocyanin - absorb green, yellow, orange

200 species of bacteria Unicellular or form filaments of cells (largely independent still) - some even form mats Contain many internal folded membranes which is where photosynthesis occurs Chlorophyll a with carotenoids and phycobilins (phycocyanin) - produces blue-green colour which gives them their other name blue-green algae Terrestrial, freshwater, marine Stromatolites: mounds of cyanobacteria that grow in tidal flats (rare) Lower cyanobacteria layers die with no light but provide a foundation for other layers to grow to a macroscopic size Fossilised stromatolites have very similar cyanobacteria to what we have together (3.5 billion yo) Nitrogen fixation: anabeana forms filaments with interspersed heterocysts which do not photosynthesise but fix atmospheric nitrogen into an organic form that can be used by other organisms Humans exploit this - rice paddies are flooded and blooms of cyanobacteria appear, then the paddies are drained killing the cyanobacteria and allowing the plants to use the nitrogen increasing yield

Marine habitats but also freshwater Chlorophyll a and c plus carotenoids (reg, brown, gold colour) Single-celled with an equatorial groove with one flagellum inside and one outside which produces a rolling movement Symbiotic with animal groups like corals, sponges, jellyfish and flatworms Often toxic and their blooms produce “red tides”

Single celled with flagella Predators, parasites and only few are photosynthetic autotrophs Chlorophyll a and b

glaucophytes, red algae, green algae,

retain some cellular features of endosymbiotic origin of chloroplasts Not very diverse: three genera Chlorophytes retain two features of cyanobacteria: chlorophyl a with phycocyanin and phycoerythrin) Chloroplast walls are similar to cell walls of cyanobacteria (made of peptidoglycan) which is absent in red and green algae as those chloroplasts are protected by the eukaryote and don’t need a wall - fossil of endosymbiosis

Some unicellular but most are complex multicellular organisms Some freshwater but most are tropical marine Cell walls are made cellulose fibres in a agar or carrageenan matrix Pigments: chlorophyl a and phycobilins which usually mask chlorophyl a and make algae red (allows them to be deep water specialists where blue light is present) Complex and unusual sexual life cycle with 1 multicellular haploid phase and 2 multicellular diploid phases Why not colonise the land? Accessory pigments are ecologically advantageous in deep waters where blue light predominates and there is not enough blue light on land

Pigments: chlorophyl a and b Two main groups: chlorophytes and streptophytes diverged 1200-725 million years ago

Pigments: chlorophyl a and b Two main groups: chlorophytes and streptophytes diverged 1200-725 million years ago

• freshwater and marine • single celled and multicelled • photosynthesise

• green algae and land plants • single celled to multicelled • many still live in aqueous habitats • some have evolved to land

zygote is often a resting stage as it has a protective coat (sporopollen) and is retained on the parent plant to receive nutrients

Opportunity: ecological gradient of freshwater to land is less steep than ocean to land (what water there is on the land in rain and pools is fresh) Sporopollen: forms zygote coat and land plants use this mechanism to coat their spores Synthetic pathways for protective biochemicals such as phenylpropanoids: protects from UV (much harsher on land than in water)

chl a and phycobillins

a and phycobillins

a (sometimes c), phycobillins and carotenoids

a + b and caretenoids