Algae Notes: If it’s not on here, you don’t need to know it for the test.
Definitions
Morphological Classifications
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Single cell
Filamentous – cells arranged end to end in a line
True branching – cells branch off of main filament, with continuation between cells
False branching - cells appear to branch off of main filament, but there is no continuation
between cells
Branching patters – you already know alternate, opposite, whorled, etc.
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Pectinate – all new branches emerge from only one side of the algae
Sympoidal – as the main axis grows it eventually terminates and becomes a branch, while a
separate branch grows and becomes the new main axis. These algae display a zig-zag like
growth pattern.
Substrate Classifications
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Saxicolus – grows on rock
Psammophilic – grows on sand
Epiphytic – growing on top of another organisms
Endophytic – growing within another organism
Planktonic – free living
Life history: many algae display a biphasic life history, with free living haploid and diploid phases. These
phases may be;
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Isomorphic: both phases have similar morphology
Heteromorphic: phases show differing morphology
Cyanobacteria
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Prokaryotes
Often form filaments, which are composed of a trichome (a hair-like structure made up of the
individual cells) and a muscilagenous sheath.
May possess akinetes (thick walled resting spores) or heterocysts (non-photosynthetic cells
where N2 fixation may take place).
o Heterocysts are necessary since the nitrogenase enzyme is inhibited by O2, which is
produced by photosynthesis. An alternative strategy is to allow N2 fixation at night
when photosynthesis is not taking place.
Green algae
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Ancestors of terrestrial plants (algae closest to modern plants are the Charophyta)
Thylakoids stacked ~20 times
Accessory pigments: chlorophyll b
Storage product: Starch (turns black when stained with iodine)
Red algae
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Thylakoids unstacked
Accessory pigments: carotenoids
Storage product: Floridean starch
Some species display a triphasic life history where, after syngamy occurs, the newly formed
spore is cloned via mitotic division within a specialized structure called a carposporophyte. As
red algae gametes are unflagellated, this increases reproduction rates when a sperm does
manage to meet an egg.
Brown algae
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Thylakoids stacked 3 times
Accessory pigments: fucoxanthin, chlorophyll c
Storage product: Laminarin
Only algae group to possess “vascular tissue”, in the form of sieve elements and sieve plates.
These allow translocation of nutrients from the bottom of the algae to the top, and of
photosynthate from the top of the algae to the bottom.
Diatoms
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Planktonic single cells, but may form colonial chains
Two main groups are the penales (pennate or pen-shaped) and centrales (centric or circleshaped)
Possess a SiO2 skeleton called a frustule, which is composed of an epithecum (the bigger of the
two halves) and a hypothecum (the smaller). Pennate species possess a line between these
halves called a raphe.
Can reproduce asexually. The frustule halves separate and each half forms a new individual.
What was the hypothecum becomes the epithecum of the new diatom. Over time, this causes
the average size of individuals within the population to decrease.
Dinoflagellates
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Planktonic single cells, some species are heterotrophic
Possess two flagella called undulopodia.
Produce toxins and are responsible for red tides.
Some species are bioluminescent, producing light when disturbed by motion. It is thought this
is a mechanism for signaling for between cells or as a method of herbivore defense.