Morphology of plant-like protists
Plant – like protists are very diverse morphologically . some are unicellular ,whereas others attach end –to – end to from long filaments or assemble into spherical colonies. Some are multicellular and from larg, macroscopic seaweeds that may be more than one hundred meters long. Cell of most plant- like protists are surrounded by a rigid cell wall made of cellulose. A few do not have a cell wall and some have a cell wall containing other materials , such as agar. ( recall from chapter 3 that agar is a complex polysaccharide extracted from certain marine red algae and used by microbiologists as the solidifying agent for culture media) . Agar also may be in - croporated into jams and jellies to increase their viscosity . Many plant – like protists also have a polysaccharide layer covering the cell wall.Cells of plant – like protists contain the chloroplasts that perform photosynthesis . However,there is great varia- tion in chloroplast morphology and in the number of chloroplasts per cell. For example, in the filamentous spir – ogyra, there is one spiral chloroplast. In another filamentous plant – like protest, zygnema, there are two star- shaped chloroplasts (see figure 12.3) . Plant – like protists also store nutrients intracellularly. Depending on the particular pro – tist, these internal reserves may be starch, fats,or oils. In plant – like protists that accumulate starch reserves,starch formation takes place in specially differentiated regions of the chloroplast called pyrenoids. Most plant – like protists are motile , although some have only a motile , although some have only a motile reproductive stage in their life cycle. Motility usually is accomplished by 9+2 eucaryotic flagella,but the number and position of the flagella varies.