The Genus Paramecium
is commonly found throughout the world, in fresh and marine water containing
bacteria and decaying organic matter. Paramecium is a small
unicellular organism. It is elongated
and ranges in size from 120 to 300
microns. The outside of the cell is
covered with a tough pellicle. Label
the pellicle. The posterior half is slightly wider than the anterior half and is bluntly pointed, while the anterior end is
rounded. On its underside there is a
large and long groove running about
half the length of its body. The outer
surface of the organism is covered with many hundreds of minute hair-like
projections called cilia. Label
the cilia. This large ciliate protozoan
that lives in stagnant freshwater has an oral
groove on one side that leads inward to the gullet
and eventually the mouth. Color
and label the oral groove light pink and the gullet red. Paramecia have two nuclei --- a larger macronucleus and a smaller micronucleus. The macronucleus,
which is relatively large and located near the center of the organism, and
controls most of the metabolic functions of the cell. Color and label the macronucleus
light blue. The micronucleus, which lies
partly within a depression on the oral side of the macronucleus, is involved
primarily in reproductive and hereditary functions. Color and label the micronucleus
dark blue.
Because paramecia live in water, they
require an organelle to pump out excess water so they do not lyse (burst). These organelles are the contractile vacuoles, usually one at each end, each surrounded by
several radiating canals which
collect water from the surrounding cytoplasm. Color and label BOTH contractile
vacuoles purple. The contractile
vacuoles serve a critical function of osmoregulation,
as water tends to accumulate inside the cytoplasm due to osmotic pressure. These structures are absent in marine Paramecium. Food
vacuoles, which are round in shape, contain enzymes to digest the other smaller
protozoans that the paramecium feeds on. Label and color the food vacuoles
yellow. These vacuoles can be seen at
the mouth where the food is loaded into them for digestion. Undigested food leaves through the anal
pore. Color and label the anal
pore brown. At the base of the cilia are
defensive structures called trichocysts.
These structures can discharge their contents as long threads. Label the trichocysts.