Paramecium (Gr.,paramekers, oblong, + L. caudata, tail) is a microscopic, elongated, slipper shaped, unicellular organism mostly found in freshwater ponds, pools, rivers, lakes, ditches, streams, reservoirs etc. It can be seen with the naked eyes as a whitish or grayish spot. It is a ciliate genus containing about 10 described species of different shape, size and structure.
P. caudatum is the best example to understand paramecium, because it is mostly found all over the world. It is belongs to the phylum protozoa and sub-phylum ciliophora. The class is ciliata so, it has many cilia that surrounding its body. It’s species vary in length, vary from 80 micron to 350 micron. It is widely found species distributed all over the world.
Habit & Habitat
- Paramecium lives on small micro-organisms like bacteria, diatoms, small algae and other protozoa.
- All the genus of paramecium shows holozoic nutrition.
- It is a aquatic animal found In freshwater pools like ponds, ditches, drains, tanks & rivers.
- It is abundant in stagnant water having organic materials and usually thrives well in ponds or slow running water containing aquatic plants.
Culture of Paramecium
Paramecium can easily cultured in wide mouthed jars with glass covers. The jar filled with boiled pond water of chalkey’s medium of (Nacl 80mg, NaHCO3 4mg, KCl 4mg, CaCl2 4mg, CaH4 (PO4) H2O 1.6mg, dissolved in one liter of distilled water) and 7-12 drop of slim-milk added weekly. The jars are must kept away from the direct sun light. This result of the process bacteria flourished which serve as food for the multiplying paramecica.
External Structure of Paramecium
The external structure of Paramecium consists of oral groove, Pellicle, and cilia.
The shape of paramecium like a slipper, hence it is called slipper-animalcule. The anterior end of the animal is blunt & posterior pointed. Joblot assigned the name ‘chausson’ to paramecium caudatum which has means slipper-shaped animalcule. In the cross section section it circular with great diameter behind the center of the body. The anterior half of the body is slightly twisted. The body is distinguished into an oval or ventral surface and aboral or dorsal surface.
The size of paramecium is microscopic and elongated. So, they are measured in micrometer in the microscope. Its species vary in length from 80 micron to 350 micron.
P. caudatum is largest species among all species of paramecium which is measured between 170 micron to 290 micron long. The greater diameter of the cylindrical body is about two-third of its entire length.
The size of different species of paramecium;
- P. caudatum (species) – 170 micron long.
- P. aurelia (species) -120-250 micron long
- P. trichidum (species) – 60 micron long.
The ventral surface of the paramecium body bears a prominent, oblique, and shallow depression called oral groove. It is originates from the middle of the body and extends to the left side of anterior end. The oral groove leads into a deeper conical vestibule at the posterior region. Which is meets with the buccal cavity having a basal mouth or cytosome (cyto-, cell and stome-, mouth).
Pellicle is a living, clear, firm and elastic cuticular membrane. It is externally found on the body. When stained specimen of pellicle observed under light microscope, it appears a regular series as polygon or hexagon with their raised rims. A single cilium comes out from the middle of each polygon or circumciliary space.
In 1959, ‘Ehret‘ and ‘Powers‘ have revealed with the help of electron microscope that the polygons are defined by a corresponding regular series of cavities which is know as alveoli. In fact it is the centre of the each alveolus which forms a polygon. The group of all alveoli form a continuous layer called alveolar layer. The alveolar layer contain an inner and outer membrane. The outer alveolar layer lie attached to the outer cell membrane and the inner alveolar lie at the inner cell membrane. Thus the pellicle of paramecium contain three membrane (i) outer cell membrane (ii) outer alveolar membrane (iii) inner alveolar membrane.
Cilia (singular cilium)
Cilia (singular cilium) are numerous tiny hair like fine projection locomotory organelles found on the body surface which covers the entire body surface of the paramecium. These are measured 10 to 12 micron in length and 0.27 micron in diameter. The number of cilia range from 10,000 to 14,000. It is also found on another eukaryotic cells. The number of cilia differ according to the the body of microbes. In caudatum, cilia of the posterior end of the body are long and form caudal tuft. hence the species is called paramecium caudatum.
Overview of cilium
- Each cilium arises from a basal body.
- The basal body is located below the pellicle.
- From each basal body arises a kinetodesmata, which runs parallel to the pellicle.
- At one place more than kinetodesmata are present.
- Each cilium is made up of microtubules.
- Microtubules show a 9:2 (ratio) arrangement.
- 9 pairs of peripheral and 2 central microtubules are present.
Internal Structure of Paramecium
The cytoplasm is a clear fluid like substance which is clearly differentiated into two regions – outer clear ectoplasm and inner granular endoplasm.
(i) Ectoplasm: The clear, narrow, peripheral and dense zone is called the ecroplasm or cortex. It consist a structure of the infraciliary system and the trichocysts.
(ii) Endoplasm: The granular, large,central and semi-fluid zone is called ectoplasm or medulla. It consist usual organelles of cell like mitochondria, ribosomes, and Golgi bodies. It also contain food particles, crystals etc.
- These are small spindle-shaped structures present perpendicular to the pellicle.
- It opens out by a pore present on the pellicle.
- Each trichocyst has a pointed tip and broad shaft.
- The tip contains a spike-covered by a cap.
- The spike arises from a basal structure.
- The shaft contains a swelling substance.
- The trichocyst is discharged when the animal is irritated.
- The discharged trichocyst is about 40 microns long.
- The discharge of trichocyst is associated with removal of cap & swelling of substance.
- The function of tricocyst is work as the organelles of defense.
The endoplasm contains two types of nuclei.
- Macronucleus or meganucleus: It is very large and bean-shaped. It is without a nuclear membrane and is vegetative in function.
- Micronucleus: They are smaller and reproductive. The number of micronucleus is different in different species of paramecium.
Some species of paramecium containing different number of nucleus are given below;
- Paramecium caudatum: having one nucleus.
- Paramecium aurelia: having two nuclei.
- Paramecium multinucleatum: many Micronucleus is surrounded by a nuclear membrane.
- Contractile vacuoles are found in freshwater protozoa for osmoregulation.
- There are two contractile vacuoles are anterior and posterior.
- Each contractile vacuole has a central reservoir surrounded by 6-8 radiating canals.
- The central vacuoles open outside by a permanent pore present on the pellicle.
- The radial canals collect excess water and release them into the central vacuole.
- The vacuole in this stage is called to be in diastole.
- The vacuole contracts to discharge water out of the body.
- The contracted vacuole is called to be in the systole stage.
The endoplasm contains numerous food vacuoles containing ingested food.
On the ventral surface, a large groove called the oral groove is present. The oral groove leads into a conical vestibule through a narrow aperture cytostome. The cytostome opens into a cytopharynx.
Locomotion in Paramecium
Progression in a medium is called locomotion. Locomotion in Paramecium takes place by cilia (ciliary locomotion). Cilia beat in a pendulum-like fashion or oar like fashion. It has an effective stroke and a recovery stroke. During the effective stroke, cilia are rigid and move backwards and in recovery stroke, it becomes limp (flexible) and moves forward.
All the cilia of the body do not beat simultaneously. The cilia of transverse row beat synchronously and that of longitudinal row beat metachronously. As a result, the paramecium does not move in a straight path, rather it takes a spiral path like a bullet. The cilia beat about 10-11 times per second. Energy for beating is obtained from ATP (Adenosine triphosphate).
Paramecium moves very rapidly at the rate of about 246711 microns per second.
Nutrition in Paramecium
Paramecium feeds on small microorganism suspended in water like bacteria, diatoms, small algae and other protozoa.
Feeding apparatus of paramecium is structurally found as an oral groove on one side of the body. It leads to a chamber Vestibule. The vestibule opens by a large opening the buccal cavity into a cytostome. All the Apparatus are lined with long Cilia.
Mechanism of feeding
During feeding, the cilia of the oral groove beat more strongly than other cilia of body. It produces a strong current of water which directed towards the oral groove. This water contains food materials as their need.
When the current of water enters vestibule, the cilia present that reject large food materials. Small food is directed into cytostome through the buccal cavity.
Formation of food Vacuole
Through cytostome, food passes into cytopharynx. When it becomes filled, a food vacuole is separated into the cytoplasm.
Digestion and Assimilation
- Digestion is intracellular. The cytoplasm shows a streaming movement called cyclosis. In this, food vacuoles first travel backwards and then again backward.
- Digestion takes place during cyclosis.
- Digestive enzymes are contained in lysosomes.
- The digestion first takes place in alkaline medium followed by digestion in acidic medium.
- The digested food passes out into the cytoplasm. This is called assimilation.
Respiration and Excretion
The undigested food is expelled out through an opening called cytopyge. It is located posterior to cytostome.
If you are interested in biology also read this notes – Structure of a Sperm Cell, Essay on Spermatogenesis.
If you are interested in biology also read this notes – Structure of a Sperm Cell, Essay on Spermatogenesis