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Lecture 21

BIOL 2004 Lecture 21: Macroalgae

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BIOL 2004
Gunawardena Arunika

Lecture 21 - Macroalgae April 4, 2017 1:11 PM Macroalgae  Larger 'plant-like' algae  Usually: o Attached o Macroscopic o Composted of many cells and/or differentiated  Diverse - several independent evolutionary origins  Different than land plants o Land plants:  Gravity is important  Shear forces 'low'  Water from soil  Most nutrients from soil  Root system, transpiration o Macroalgae  Gravity often trivial (buoyancy in water)  Shear forces often very high  Water abundant  Nutrients from surrounding fluid  Basic structure o Main 'body' of alga - thallus (plural - thalli)  Filamentous form (each filament usually one or a few cells thick)  Grows in simple and branching filaments - typically grow via repeated division of apical meristematic cells (one main plane of division per filament)  Another growth method is thickened or feathery filaments - limited (determinate) lateral division  Sheet-like form (usually 1-2 cells thick)  Fleshy form (often differentiate within thallus - often only the outer cell layers are photosynthetically active, while inner cell layers perform other functions)  Pseudoparenchymatous - grows as filaments of cells but embedded within a common extracellular matrix (imagine a glove in a mitten)  Parenchymatous - cell division in more than two planes from meristems  Produce true 'tissues' o Alga usually attaches to (or into) substrate by 'holdfast' (or rhizoid)  Cell walls/Extracellular matrix o Often large percentage of thallus volume o Important in determining the structural properties of thallus o Polysaccharides are a major component  Cellulose - common  Sulfated polysaccharides in red algae  Intercellular connections o Plasmodesmata - connection between each cell membrane  In many chloroplastidan macroalgae, and some brown algae o Pit plugs - a protein that connects cell membranes  Primarily mechanical connection  Red algae has these  Lifecycles o Often (but not always) alternation of generations o Sporophyte and gametophyte can be isomorphic (similar) or heteromorphic (different in size and form)  Gametes o Isogamy (a) = same sized gametes o Anisogamy (b) = one is bigger than the other o Oogamy (c) = ovum instead of just an egg Macroalgal Ulvophyceae  Main 'green' macroalgae in marine habitats  Up to ~1 meter long - many with simple thalli  Ex. Ulva - simple sheet-like thallus, 2 cells thick  Caulerpales (e.g. Codium) o Some with complex, thick thalli o Siphonous - continuous multinucleate cytoplasm branches through thallus Rhodophyta (Rhodophytes, Red Algae)  Large grou
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