The protist called paramecium boasts an efficient way of getting around via cilia. Cilia are also used in helping a paramecium eat. Paramecia use cilia first to draw food particles in, and they then use phagocytosis to begin the digestion process.
TL;DR (Too Long; Didn't Read)
The paramecium is a unicellular protist that uses its cilia to pull food into its oral groove. Food particles are then digested via a process called phagocytosis.
What Is a Paramecium?
A paramecium is a protist, an organism that is neither plant nor animal. The paramecium belongs in kingdom Protista, phylum Ciliophora and family Paramecidae. In the paramecium kingdom Protista, protists are eukaryotes, and they come in many different sizes and shapes. They can range from microscopic, unicellular organisms to giant kelp.
As for a paramecium, it is quite small, though easily visible under a microscope. It is one of the larger microscope protists, approximately 0.5 millimeters in length. Paramecia are unicellular, or singled-celled. They possess one nucleus.
Some examples of paramecia species include Paramecium caudatum, Paramecium bursaria and Paramecium multimicronucleatum.
Features of Paramecia
A paramecium is an oblong-shaped swimmer. The paramecium possesses many little appendages called cilia all on the outside of its body. These are used to help the paramecium move around. This is in contrast to Euglena, which use a tail-like object called a flagellum. Amoebas, on the other hand, use appendages called pseudopodia to get around.
Many protists like to live in fluid environments like ponds or lakes. The paramecium is no exception, and it can move at fast speeds in its liquid environment.
Paramecia prefer to live in liquid habitats that are 78 degrees Fahrenheit or below in temperature.
Is a Paramecium an Autotroph or a Heterotroph?
Different protists use different ways of eating. Those that can make their own food via photosynthesis are called autotrophs. Those protists that need to hunt for food and eat it are called heterotrophs. Heterotrophic behavior describes the manner in which nutrition in paramecium is obtained.
Paramecium bursaria, interestingly, contains symbiotic organisms that conduct photosynthesis. In its case it only requires a good light source so that its symbionts can make food for it.
Sources of Nutrition in Paramecium
A paramecium gains nutrition by eating other microbes such as bacteria and fungi, among other organic material. They will even eat other protists, such as Chilomonas; in fact this is one of their favored prey.
Sometimes paramecia consume pathogens that are harmful to other organisms. Paramecia are not picky eaters, however. But they do eat better under cooler conditions.
Paramecia themselves provide food for other animals as well, from tiny rotifers on up.
The Roles of Cilia in Paramecia
Hair-like fibers called cilia are found in vast numbers of organisms. For microscopic organisms, they play crucial roles for motility and survival.
Cilia function in two different ways for paramecia. They can be used to help a paramecium move, or to help it eat, depending on its needs at the time. The cilia all work via molecular motors.
Cilia resemble hairs in their shape. However, they are actually a type of cellular organelle that extends outside of a paramecium's cell body. Paramecia are covered with these cilia, and the cilia help the cell move around in a fluid by thrusting like infinitesimal oars.
Under different viscosity conditions, cilia behave differently. If a paramecium is in a thick, more viscous fluid, the cilia meant for movement slow down.
Cilia also function to help obtain nutrition in a paramecium. This occurs in the oral groove in the paramecium.
The Oral Groove in Paramecium
The oral groove in a paramecium is a notch in its body. It is lined with cilia that, rather than for moving the paramecium around, are used for sweeping nutrition sources into the cell.
Researchers now know that the cilia of the oral groove operate in a different manner than the cilia that surround the paramecium for motility. Also, in conditions of increased viscosity, the oral groove cilia do not slow down as much as the motility cilia do.
In general, the two kinds of cilia look quite similar. However, scientists think the actual molecular motors of oral groove cilia must be different from motility cilia.
The oral groove leads to the food storage area of the paramecium, the cytostome.
What Is Phagocytosis?
Phagocytosis represents the manner in which food can be taken in for nutrition in paramecium. This occurs when a food particle becomes engulfed by the cell’s membrane. Elie Metchnikoff first discovered phagocytosis. Metchnikoff found that different digestive parts of a paramecium contain different acidity.
The cell membrane of the paramecium will wrap around the food particle, pull it inside the membrane and then pinch it off. This little sac is the food vacuole.
In protists like paramecium, vacuoles are used to store a food particle in the cytoplasm. The vacuole with the food particle is called a phagosome. This phagosome will fuse with a lysosome, with special enzymes. These enzymes operate only in highly acidic conditions; their containment keeps the paramecium from being damaged. The resulting phagolysosome then goes on to digest the food for use in the cell.
Waste Removal in Paramecium
Once all the nutrition in paramecium digestion is obtained, any waste material must be ejected from the cell. This process is called exocytosis.
Unicellular organisms like the paramecium must work constantly to provide a balance of fluids. Because paramecia tend to live in fresh water, the challenge is to prevent too much water entering the saltier environs of the inside of the cell. If too much water intrudes, the paramecium could burst.
To work around this issue, fortunately paramecia are able to harness a contractile vacuole to maintain fluid balance. This is an organelle that is used to collect excess fluids and dump them out. It does the same thing for other forms of waste, using its little collector tubes and contracting them to purge.
Paramecia also get rid of waste such as nitrogen by simply letting it escape through the cell membrane via diffusion.
Studying Paramecium Digestion
One appealing feature of paramecia is their suitability as laboratory subject matter in classrooms. They are small in size, easily ordered and shipped, and are relatively low-maintenance.
Paramecia are fairly clear, providing students with a visible display of the paramecia's interiors. They need a climate-controlled space but otherwise prove to be ideal for studying cellular processes. They move very quickly on slides. So to observe them more easily, in some cases they may need to be slowed down with a special substance like petroleum jelly.
To study protist digestion, instructors can provide paramecia and have them consume various indicators. These color the vacuoles and other organelles in a paramecium, according to the pH (concentration of hydrogen ions) inside of the organelles.
A lower pH reading indicates higher acidity inside a vacuole. A higher pH indicates a more basic, less acidic vacuole and so on. Students can watch actual digestion as the food vacuoles change in color in real time.
Because lysosomes require high acidity to assist in digestion on a paramecium, students can expect to see a lower pH for that activity. All in all, the paramecium provides an elegant opportunity to learn about cell behavior, simple digestive processes and how the pH of interior of the cell differs.
About the Author
J. Dianne Dotson is a science writer with a degree in zoology/ecology and evolutionary biology. She spent nine years working in laboratory and clinical research. A lifelong writer, Dianne is also a content manager and science fiction and fantasy novelist. Dianne features science as well as writing topics on her website, jdiannedotson.com.