SCIENCE: PARAMECIUM

WHAT IS A PARAMECIUM?

A paramecium is a small (unicellular) living organism that can move, digest food, and reproduce. They belong to the kingdom of Protista, which is a group (family) of similar living micro-organisms.  Micro-organism means they are a very small living cell. You might be able to see one as a tiny moving speck if your eyesight is extremely good but for any detail at all you need a microscope to look at and study them.  They are about .02 inches long (.5mm). They are also famous for their predator-prey relationship with Didinium. Paramecium are known for their avoidance behavior. If an encounters a negative stimiulus, it is capable of rotating up to 360 degrees to find an escape route. Didinium are heterotrophic organisms. They only have one type of prey; the much larger cilate Paramecium. When a Didinium finds a Paramecium, it ejects poison darts (trichocysts) and attachment lines. The Didinium then proceeds to engulf its prey. Although Paramecium are larger than they are, Didinium are voracious eaters and will be ready to hunt for another meal after only a few hours.

WHAT DOES A PARAMECIUM LOOK LIKE?
The paramecium is an oval, slipper shaped micro-organism, rounded at the front/top and pointed at the back/bottom. The pellicle, a stiff but elastic membrane that gives the paramecium a definite shape but allows some small changes. Covering the pellicle are many tiny hairs, called cilia. On the side beginning near the front end and continuing half way down is the oral groove. The rear opening is called the anal pore. The contractile vacuole and the radiating canals are also found on the outside of a paramecium.  Inside the paramecium is cytoplasm, trichocysts, the gullet, food vacuoles, the macronucleus, and the micronucleus.  Study the drawing below.

Pellicle - a membrane covering that protects the paramecium like skin Cilia - hair like appendages that help the paramecium move food into the oral groove Oral Groove - collects and directs food into the cell mouth Cell Mouth - opening for food Anal Pore - disposes of waste Contractile Vacuole - contracts and forces extra water out of the cell Radiating Canals - paths to the contractile vacuole Cytoplasm - intercellular fluid needed to contain vital cell parts Trichocyst - used for defense Gullet - forms food vacuoles Food Vacuole - storage pocket for food Macronucleus - larger nucleus which performs normal cell functions Micronucleus - smaller nucleus which is responsible for cell division.

Now look at the still microscope image below and see if you can pick out the various paramecium parts.

Image courtesy: BioMEDIA ASSOCIATES
The paramecium, genus of protozoa of the phylum Ciliophora, is often called slipper animalcules because of their slipper-like shape. Paramecia are unicellular organisms usually less than 0.25 mm (0.01 in) in length and covered with minute hair-like projections called cilia. Cilia are used in locomotion and during feeding. When moving through the water, paramecia follow a spiral path while rotating on the long axis. When a paramecium encounters an obstacle, it exhibits the so-called avoidance reaction: It backs away at an angle and starts off in a new direction. Paramecia feed mostly on bacteria, which are driven into the gullet by the cilia. Two contractile vacuoles regulate osmotic pressure (see  Osmosis) and also serve as excretory structures. A paramecium has a large nucleus called a macronucleus, without which it cannot survive, and one or two small nuclei called micronuclei, without which it cannot reproduce sexually. Reproduction is usually asexual by transverse binary fission, occasionally sexual by conjugation, and rarely by endomixis, a process involving total nuclear reorganization of individual organisms.  Macronuclear DNA in Parameciumhas a very high gene density. The macronucleus can contain up to 800 copies of each gene. Paramecia abound in freshwater ponds throughout the world; one species lives in marine waters. They are easily cultivated in the laboratory by allowing vegetable matter to stand in water for a few days. The common species Paramecium caudatum is widely used in research.

HOW DOES A PARAMECIUM MOVE?

The paramecium swims by beating the cilia. The paramecium moves by spiraling through the water on an invisible axis. For the paramecium to move backward, the cilia simply beat forward on an angle.   If the paramecium runs into a solid object the cilia change direction and beat forward, causing the paramecium to go backward. The paramecium turns slightly and goes forward again. If it runs into the solid object again it will repeat this process until it can get past the object.

HOW DOES A PARAMECIUM EAT?

Paramecium feed on microorganisms like bacteria, algae, and yeasts. The paramecium uses its cilia to sweep the food along with some water into the cell mouth after it falls into the oral groove. The food goes through the cell mouth into the gullet. When there is enough food in it so that it has reached a certain size it breaks away and forms a food vacuole. The food vacuole travels through the cell, through the back end first. As it moves along enzymes from the cytoplasm enter the vacuole and digest it. The digested food then goes into the cytoplasm and the vacuole gets smaller and smaller. When the vacuole reaches the anal pore the remaining undigested waste is removed. Paramecium may eject trichocyts when they detect food, in order to better capture their prey. These trichocyts are filled with protiens. Trichocysts can also be used as a method of self-defense. Paramecium are heterotrophs. Their common form of prey is bacteria. A single organism has the ability to eat 5,000 bacteria a day. They are also known to feed on yeasts, algae, and small protozoa.Paramecium capture their prey through phagocytosis.

WHAT SENSES DO PARAMECIUM HAVE?
The paramecium can not see, taste, touch, or hear.  However, It evidently has some sense of  movement because it responds when it bumps into something.  It also can sense certain chemicals, as noted in: Chemosensory Signal Transduction in Paramecium

HOW DO PARAMECIUM REPRODUCE?

Paramecium are capable of both sexual and asexual reproduction. Asexual reproduction is the most common, and this is accomplished by the organism dividing transversely. The macronucleus elongates and splits. Under ideal conditions, Paramecium can reproduce asexually two or three times a day. Normally, Paramecium only reproduce sexually under stressful conditions. This occurs via gamete agglutination and fusion. Two Paramecium join together and their respective micronuclei undergo meiosis. Three of the resulting nuceli disintegrate, the fourth undergoes mitosis. Daughter nuclei fuse and the cells separate. The old macronucleus disintegrates and a new one is formed. This process is usually followed by asexual reproduction.

WHERE DO PARAMECIUM LIVE?

Paramecium live in aquatic environments, usually in stagnant, warm water. The species Paramecium bursaria forms symbiotic relationships with green algae. The algae live in its cytoplasm. Algal photosynthesis provides a food source for Paramecium. Some species form relationships with bacteria. For example, Paramecium caudatum hosts Holospora obtusa in its macronucleus. This bacteria is specific to the macronucleus of Paramecium caudatum; they cannot grow outside of this organism. This species acquires heat-shock resistance when infected with Holospora obtusa, which contributes to ciliary motion. Paramecium are also well known as prey for Didinium.
Paramecia play a role in the carbon cycle because the bacteria they eat are often found on decaying plants. Paramecium will eat the decaying plant matter in addition to the bacteria, further aiding decomposition.
Paramecia can be used as model organisms in research. Currently, they are being used a great deal in genetics research. For example, recent research involves inactivating Paramecium genes for studying functional analysis by homology-dependent gene silencing. They can also be used to study membrane excitability and the duplication of basal bodies.
CAN PARAMECIUM COMMUNICATE?
Read about this experimentation of the ability of a paramecium caudatum communicating through glass.  Daniel Fels documents the interactions among different populations of a single-celled ciliate,Paramecium caudatum, seperated by glass.  Because the glass barriers effectively prohibit the transfer of chemical signals, Fels infers that these simple organisms are using a form of weak electromagnetic radiation, so-called biophotons, to communicate.
Source:
http://101science.com/paramecium.htm