Study Of Paramecium

Paramecium caudatum is commonly found in freshwater ponds, pools, ditches, streams, lakes, reservoirs and rivers. It is specially found in abundance in stagnant ponds rich in decaying matter, in organic infusions, and in the sewage water Paramecium caudatum is a free living up to 300 – 350 microns.
P. caudatum looks like the sole of a slipper or shoe, hence, the animals in commonly known as slipper animalcule. The body of the animal is asymmetrical in form showing a well defined oral or ventral surface and an aboral or dorsal one. The body is covered by a thin, double layered, elastic and firm pellicle made of gelatin.
The pellicle holds the shape of the animal but is elastic enough to permit contractions. The entire body is covered with numerous, small, hair-like projections called cilia. When the cilia occur in longitudinal rows all over the body: then it is holotrichous, in which the body cilia are equal.

The cilia arise from kinetosomes and from where arises a delicate cytoplasmic fibril called kinetodesma. Oral groove or peristome is situated on the ventrolateral side, which give the animal an asymmetrical appearance. The oral groove leads into a short conical funnel shaped depression called vestibule that leads directly into the cytostome. Extending directly from the cytostome toward the entire of the body is the wide cytopharynx that turns sharply towards the posterior side to become the slender tapering oesophagus.
The cytoplasm is differentiated into a narrow, external or cortical zone called the ectoplasm and a larger, internal or medullary region called the endoplasm .Trichocysts are the spindle shaped bags embedded in the ectoplasm. The endoplasm or medulla is the more fluid and voluminous part of the cytoplasm which contains many cytoplasmic granules.
Paramecium is heterokaryotic having a large ellipsoidal and granular macronucleus and other small compact micronucleus.
There are two large, liquid filled contractile vacuoles which are roughly spherical, non contractile bodies. They contain ingested food particles, principally bacteria and a small amount of fluid bounded by a thin definite. Paramecium performs locomotion by two methods, viz., metaboly or body contortions and by cilia .Locomotion brought about by cilia is the main method. The cilia can beat forwards or backwards enabling the animal to swim anteriorly or posteriorly. Cilia of the same transverse row beat together and those of the same longitudinal row beat one after the other from the anterior to the posterior end. This is called metachronal rhythm. In Paramecium nutrition is holozoic. The food comprises chiefly bacteria and minute Protozoa.
During Cyclosis digestion occurs by enzymes secreted by protoplasm into the vacuoles. In digestion proteins are changed into amino acids, carbohydrates and fats. The undigested matter is egested through the cytopyge. The exchange of gases (Oxygen and carbon dioxide) takes place through the semi permeable pellicle by the process of diffusion.
Paramecium obtains its oxygen from the surrounding water. Carbon dioxide and organic wastes like ammonia are excreted by diffusion outward into the water in the reverse direction. The responses of Paramecium to various kinds to stimuli are learned by study of its reactions and of the grouping or scattering of individuals in a culture. The response is positive negative when it moves away. In avoiding reaction the ciliary beat reverses, and then rotates in a conical path by swerving the anterior end aborally while pivoting on the posterior up. Response to contact is varied in Paramecium. While, i.f the anterior end is lightly touched with a fine point.

A strong avoiding reaction occurs. Generally Paramecia respond to chemical stimuli by means of avoiding reaction. Paramecia show an avoiding reaction when a temperature change occurs markedly above or below the optimal range (of 240 C to 280 C). However, when the light intensity is suddenly and sharply increased, a negative reaction is displayed .Paramecia exhibit an immediate negative response to Ultraviolet rays.
Paramecia also respond to electric stimuli and positive rheotaxis. Paramecium reproduces asexually by transverse binary fission and also undergoes several types of nuclear reorganization, such as conjugation, endomixis, autogamy, cytogamy and hemixis, etc. It is a distinctly unique asexual process in which one fully grown specimen divides into two daughter individuals without leaving a parental corps.
Paramecium reproduces by transverse binary fission during favourable conditions, fission the micronucleus divides by mitosis into two daughter micronuclei, which move to opposite ends of the cell.
The macronucleus elongates and divides transversely by amitosis. Paramecium multiplies by binary fission for long periods of time, but at intervals this may be interrupted by the joining of two animals along their oral surfaces for of conjugation.

Kappa particles

In 1938, T.M. Sonneborn repored that some races (known as killers or killer strain of Paramecium produce a poisonous substance, called paramecin which is lethal to other individuals called sensitives. The paramecin is water soluble, diffusible and depends for its production upon some particles located in the cytoplasm of the Paramecium (killer strain). These particles are called kappa particles.

Identifying features

Since the animal contains slipper-shaped body and 2 contractile vacuoles which are star-shaped and has all above features, hence it is Paramecium.

Special features

Paramecium has great experimental value in cytogenetically studies. T.M. Sonneborn sensitive strain without Kappa particles. P. aurelia is taken as example to explain cytoplasmic inheritance.