BIOL 2004 Lecture Notes - Lecture 21: Heterokont, Phloem, Rhizoid
15 Apr 2017
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Basic structure: 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. 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: alga usually attaches to (or into) substrate by "holdfast" (or rhizoid) Cell walls/extracellular matrix: often large percentage of thallus volume o o. Important in determining the structural properties of thallus. In many chloroplastidan macroalgae, and some brown algae.
