Paramecia move with the assistance of small hairs called cilia that project from all sides of their bodies. The single-celled organisms use these hairs like oars, beating them against the water to move around in pursuit of food and to avoid predators. The movements are sometimes quite interesting to watch, as they are incredibly fast, considering their size. Almost any sample of still water will contain some paramecia. They are just visible with a magnifying glass, and sometimes with the naked eye, but can be seen in some detail with a microscope at around 100 X magnification.
The way paramecia move is quite straightforward; usually, they will travel in a straight line until they bump into something and navigate around it. They may, however, change course to reach food, and it is believed that the creatures may have chemical sensors to alert them to potential sources of nutrition. Watching one move around large obstacles can remind people of navigating into small parking spaces, as it moves forward, backs up, turn, moves forward, and so forth until it in the clear again.
The cilia on a paramecium move in two directions. The creatures move forwards by beating their cilia at a backward angle, to thrust themselves through the water. To back up, they beat forwards. They also spin as they swim through the water, allowing them to collect food, which is pushed by the cilia into the mouth. A paramecium can look like a twirling top as it spirals through the water.
How Cilia Work
Many other single-celled organisms use cilia for propulsion, and some use a flagellum — a single, long, whip-like appendage. The two are quite similar in design, and operate in the same way. Although they appear to be just simple hairs, their structure is in fact quite complex.
A cilium consists of a hollow, flexible cylinder, made from nine pairs of tiny tubes known as microtubules. Another pair of microtubules runs through the center, connected to the surface by spokes. Each pair of microtubules has two protein molecules, known as dynein arms, attached to it at intervals along its length. These act like tiny motors, using adenosine triphosphate (ATP) as a source of energy. To achieve movement, they push in unison against the neighboring microtubule pair, causing it to bend in the desired direction.
This happens very quickly, and the combined action of these little motors causes the cilium as a whole to bend one way or the other, as required. Together, the coordinated action of many cilia can propel a paramecium at quite a speed, often making them difficult to observe clearly. The fine details of cilia cannot be seen with an ordinary microscope — their structure was revealed by examining cross sections using powerful electron microscopes. The study of cilia may help with the design of useful nanomachines.
Paramecia can usually be obtained from pond or ditch water, especially near decaying vegetation such as dead leaves, which provide a rich food source in the form of bacteria and other microorganisms. A drop of this water placed on a microscope slide, with a cover slip on top, will usually reveal these little creatures. To see the cilia well, a magnification of perhaps 300-400 times is best, and it may be necessary to adjust the lighting to highlight these tiny, transparent structures.
A common problem with observing paramecia, especially at higher magnifications, is that they simply move too fast for their detailed structure to be clearly seen. Scientists, therefore, sometimes resort to various methods of slowing them down. These include using viscous fluids, and providing food, such as yeast, which they will graze upon, reducing their movements.
Interesting Paramecium Facts
A paramecium is shaped roughly like a shoe or slipper, with a covering of cilia and a groove that acts as a mouth. The beating of the cilia, aside from providing propulsion, also creates currents in the water that drive food particles into the “mouth.” Despite being single celled, the organism is quite complex, with a nucleus containing genetic material, and easily identifiable organelles — miniature organs.
Among these are one or more contractile vacuoles, which gather and expel excess water. Food particles, once “swallowed,” form food vacuoles: little “bags” that surround the food and through which nutrients are absorbed. By feeding paramecia yeast stained with a dye, the formation and progress of these vacuoles can be followed. Like most other single-celled organisms, paramecia usually reproduce by simply dividing in two — the nucleus splits first, duplicating the DNA. They are also capable of conjugation: a primitive form of sexual reproduction in which two organisms temporarily fuse together and exchange genetic material before dividing.