Eukaryotes

 

Protists

Trypanosoma gambiense (100X)  Note the spindle-shaped flagellate organisms swimming between the red blood cells. Several species of this genus are responsible for trypanosomaisis or "sleeping sickness", a form of encephalitis which occurs in infected mammals. Two species, T. gambiense and T. rhodesiense cause African trypanosomaisis in humans, the primary vector being the tse tse fly endemic to parts of Africa, and another T. cruzii is responsible for American trypanosomaisis, it vector being the reduviid (triatomid, or cone-nosed) bug endemic to Central and South America.
 
 

  Diatoms (40X)  Note the various shaped cells, dark center nuclei, and long dark green chloroplasts. Diatoms are golden-brown algaes belonging to the Division Chrysophyta. They have cell walls composed primarily of silicon dioxide and pectic acid. These are particularly important primary producers in the marine environment, and leave their silica cell wall behind after death, which over millions of years settle to form the "diatomaceous earth" used in commericial filters.
 
 

Fungi

 
 

Saccharomyces cerevisiae (100X) This is commonly called "brewers yeast", and is a good representative of the general yeast morphology. Note the presence of buds on some of the cells. Budding is an asexual division of cells represented by an unequal division of cytoplasm. Since the genetic component of the cell is copied exactly prior to division, the two progeny cells will both eventually grow to the same size. These yeasts belong to the group known as the Ascomycetes, and reproduce by budding and the formation of ascospores.

Penicillium notatum (40X)  Note the placement of the conidiospores on this fruiting body. P. notatum produces the antibiotic penicillin, which it excretes into the surrounding medium as a means of excluding competition from other microorganisms. In particular, gram positive bacteria are harmed by this antibiotic since it interferes with the activity of transpeptidase, an enzyme which links layers of peptidoglycan together during cell wall synthesis.
 
 

Aspergillus niger (40X)  This species produces conidia in a characteristic "sunburst" pattern. This mold is commonly found growing on decomposing fruits, grains, and grain products such as breads.
 
 

  Rhizopus stolonifer (40X)  This is common black bread mold.  Note that the spores are held within a sporangium (spore sac) which dries and breaks open after spore maturation.
 
 

Helminths (Parasitic round- and flatworms)

Trichinella spiralis (40X) This is the agent of trichinosis.  Note the spiral worm, surrounded by a capsule embedded in skeletal muscle tissue. The worm enters the body of the host via the consumption of raw or poorly cooked meat which has previously been infected. Sexually active worms shed eggs in the gastrointestinal tract, which are then released from the body with feces. The eggs come to rest on plants, which are eaten in turn by herbivores, repeating the cycle. Once the worm has encysted itself within muscle tissue, it can remain dormant and protected from external treatments such as antihelmithic drugs.
 
 
 

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