Introduction to some aquatic protozoa in Essex
Figure 3. Amoeba proteus under x40 objective © Steve Durr
The photograph of A. proteus in Figure 3 was taken with a x40 Nomarski objective and shows the
very granular nature of the nucleus. Various food vacuoles can also be seen in different stages of
their digestion process.
The cytoplasm of the amoeba consists of two forms, the easily flowing endoplasm which when
reaching the very tip of the pseudopodium flows outward and back round where it turns into a gel
like substance which is called the ectoplasm. This more rigid cytoplasm acts like the walls of a
toothpaste tube and squeezes the more fluid endoplasm forward. When watching amoeba for the
first time it is easy to imagine that they wander around with no purpose, careful observation will
soon prove to the contrary. The pseudopodia are put out to detect chemicals, oxygen, and temperature
along with various other variables that need to be checked out by the advancing amoeba. If the
direction in which the amoeba is advancing proves to be uninteresting then the amoeba will retract
the pseudopodia and send out an exploratory foot to check the environment in some other direction.
Water-expelling vacuoles are common to most species of freshwater amoebae and are the animal's
way of expelling excess water that may accumulate in the cell body. The filling and emptying of this
vacuole is interesting to observe under a microscope over a period of time. If you are lucky you may
see an amoeba engulfing a diatom or some other protozoan. Many amoebae usually have one or two
food vacuoles that are in various stages of digestion; and once again, it is interesting to observe their
wanderings about the cell body as the animal moves about the glass surface of the slide.
I realise that not everyone can have access to a phase contrast microscope but even with a basic light
microscope with no enhancement aids there is still much that you can observe.
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Essex Naturalist (New Series) 18 (2001)