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.
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
(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.
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.