Describe the outer cell walls of diatoms and coccolithophores What will be an ideal response?

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Apart from cyanobacteria, the most productive photosynthetic organisms in the plankton are
the diatoms. Patterns of perforations exist through the diatom’s rigid cell wall, or frustule. As
much as 95% of the mass of the frustule consists of silica, giving this heavy covering the
optical, physical, and chemical characteristics of glass. Magnification reveals that the frustule
consists of two closely matched halves, or valves, with the top valve adhering tightly over the
lip of the bottom one. The pattern of perforations, slits, striations, dots, and lines on the
surface of the valves is different for each diatom species. In contrast, coccolithophores are
small, single-celled autotrophs covered with disks of calcium carbonate (coccoliths) fixed to
the outside of their cell walls. Coccolithophores live near the ocean surface in brightly lit
areas. Their translucent covering of coccoliths may act as a sunshade to prevent absorption of
too much light. In areas of high coccolithophore productivity, most notably in the
Mediterranean and Sargasso seas, their numbers occasionally become so great that the water
appears milky or chalky.