Module 4: Cell Biology and Microbiology

Eukaryotes

Division Chrysophyta includes the lovely diatoms (approximately 10,000 species), the golden-brown algae (approximately 1,500 species), and the smaller group (approximately 600 species) of yellow-green algae. Chrysophyta are characterized by the presence of chlorophylls a and c; fucoxanthin, a yellow-brown pigment present in all except the yellow-greens; silicon-impregnated cell walls (lacking cellulose); and their storage of food as oil rather than starch.

Diatom

Diatoms are famous for their beautiful, lace-like double shells made of rigid silicon. The tracery in the shells is actually pores that allow passage of materials into and out of the alga. Diatoms, like most plankton, are an important part of the marine food chain. Unlike their Divisional relatives, which reproduce via binary fission, diatoms sometimes reproduce sexually via a fusion of gametes, called syngamy.

dinoflagellates

Division Pyrrophyta , or fire algae, is made up of about 1,000 species of single-celled, marine dinoflagellates. Most species are photoautotrophs, but some are heterotrophs; most have two flagella. Dinoflagellates come in a bewilderingly weird variety of forms, kept in shape by rigid cellulose walls. A few are naked, and most of these are parasitic. As their name suggests, most fire algae are red. They are often the culprits in occurrences of toxic red tides. Some dinoflagellates (especially Gessnerium catenellum) that form red tides release neurotoxins, which have caused massive fish kills and occasional poisoning of humans who ingest it in filter-feeding mussels and other shellfish.