A diagram of paramecium shows ciliary slipper shaped elongated structure. It can visible to the naked eyes as a whitish or greyish spot. Paramecium is often described as cigar shaped or spindle shaped.
Its body is elongated, and blunt rounded end and somewhat pointed at posterior end. In the cross section diagram, it is circular with greatest diameter behind the center of body. The body of paramecium distinguished into an oral or ventral surface and an aboral or dorsal surface.
External Diagram of Paramecium
The external diagram of paramecium shows Oral groove, Pellicle, and cilia. Before exploring the external diagram of paramecium we should know the size of paramecium.
Size of Paramecium
The size paramecium species vary in length from 80 micron to 350 micron. Paramecium caudatum is the largest species measures between 170 micron to 290 micron long. Other species of paramecium like P. aurelia, P. trichidum measured about 120 micron to 250 micron long and 60 micron long respectively.
Oral Groove in the diagram of Paramecium
The ventral surface of paramecium endure a prominent, oblique and shallow depression, called oral groove. Oral groove originates from the middle body and extends to the left side of the anterior end. The oral groove deeper in conical vestibule which forwarded in buccal cavity consist of oral cilia and basal mouth or cytosome (cyto= cell , stoma= mouth).
Pellicle in the diagram of Paramecium
Pellicle is a external covering of a living body, it is clear, firm and elastic cuticular membrane. The stained specimens of paramecium pellicle under light microscope, appears as a regular series of polygonal (or hexagonal) depression with their raised rims. Each cilium comes out from the middle of each polygon or circumciliary space.
In 1959, Ehret and Powers revealed the polygons are appearing as corresponding regular series of cavity known as alveoli. In fact, the pit in the centre of each alveolus which forms a polygons. All the alveoli form a continuous alveolar layer, which is followed by inner an outer alveolar and inner alveolar membrane.
The outer alveolar layer lies at the close contact with beneath the outer cell membrane and inner alveolar layer lies at the close contact below the cell membrane. Thus, the pellicle of paramecium include a sequence of three membrane: (i) outer cell membrane (ii) outer alveolar membrane, and (iii) inner alveolar membrane.
Cilia in the diagram of Paramecium
The term Cilia refers to numerous, tiny, external hair like fine structure of phylum Ciliata. In ciliates, paramecium, the entire body covered with numerous, fine, tiny, hair like projections are called cilia. A cilium (singular of cilia) is measured about 10- 12 micron in length and 0.27 micron in diameter.
There are 10,000 to 14,000 cilia covering the whole body of paramecium. These motile organelles are arranged in raw of regular longitudinal manner. The length of cilia are uniform except few cilia are long at the posterior end of the body forming caudal tuft hence, a particular species of paramecium known as Paramecium caudatum. A cilium has same fundamental structure as a flagellum. (see fig.). Read detailed structure of a cilium.
Internal Diagram of Paramecium
The internal diagram of paramecium includes cytoplasm, infraciliary system, trichocytes, nucleus (heterokaryotic nuclei), contractile apparatus, food vacuoles, oral apparatus, and cytopyge.
Cytoplasm in the diagram of Paramecium
The cytoplasm in the diagram of paramecium differentiated into two regions, as ectoplasm and endoplasm.
(a). Ectoplasm: The peripheral, narrow, clear, and dense zone is called ectoplasm or cortex. It includes the basal body, kinetodesmata, and trichocysts.
(b). Endoplasm: The large, central, and granular semi fluid zone is called endoplasm or medulla. It includes cell components like mitochondria, Golgi bodies, ribosomes, crystals, reverse food granules etc.
Infraciliary system of Paramecium
The infraciliary system of paramecium lies just beneath the pellicular alveoli. The infraciliary system followed by the basal bodies and kinetodesmata. (a) Basal bodies. A tube like structure produced at the base of each cilium is called basal body or kinetosome. It is formed by thick basal end of peripheral fibre of cilium.
The central fibre do not involve in it. (b) Kinetodesmata. Kinetodesmata is a system of specialized striated fibrils called kinetodesmal fibrils. The number (5 fibrils ) of fibrils are forming a bundle of overlapping longitudinal structure called kinetodesmata.
In a three dimensional electron microscopic diagram of paramecium represent a portion of pellicle and infraciliary system, where kinetodesmata lies just below the end tube of basal body of cilia. It has been suggested that fibrils coordinate ciliary beat and movement, but this evidence is very conflicting.
Trichocysts in the diagram of Paramecium
Trichocysts are pellicular rode-like oval organelles oriented at the right angles to the body surface and present throughout the ectoplasm alternating with each basal bodies. Trichocysts of paramecium are very small in size, measuring about 4 micron in length.
Each Trichocyst has elongated shaft and terminal pointed tip, called the spike or barb, covered by a cap. The matrix of elongated shaft of trichocysts consists of a dense mass of fibrous protein, called trichinin.
The function of trichocysts are not well known. Scientists believed that that function of trichocysts that these discharge and anchor the animal to a firm substratum when it feed upon bacteria but other scientists believe that, these are organelles of defence.
The chemical, mechanical electrical stimulation trigger to discharge the trichocysts. It is occurs in a few milliseconds. Fully discharged shaft of trichocysts become a long cross-striated rod and measures about 40 micron in length. It is believed that the discharge process of trichocysts consists of an infolding of the lattice of trichinin fibres.
Nucleus in the diagram of Paramecium
The diagram of Paramecium caudatum consists of two types of nuclei are macronucleus, and micronucleus.
(a). Macronucleus: It is a single, large, roughly, granular, kidney shaped structure, present slightly anterior to the middle of the body. Macronucleus is polyploid, it has inconspicuous nuclear membrane inside many nucleoli and much more chromatin materials are found. It is also somatic or vegetative nucleus that may control all activities of the cell. Macronucleus derived from micronucleus during reproductive processes.
(b). Micronucleus: The micronucleus is a compact spherical structure surrounded with nuclear membrane and located close to, or frequently lodged in shallow cavity of the macronucleus. It has diploid number of chromosomes. The interesting things is, its chromatin granules are finer than those of the macronucleus and it controls the activities of the organisms.
Micronucleus contains definite nucleolus in Paramecium aurelia, while in Paramecium caudatum the nucleolus is absent. Almost, all paramecium are heterokaryotic (hetero- different + karyon- nucleus) because it possesses two types of nuclei as shown in the diagram of Paramecium caudatum. But there are many species of paramecium exhibit on the earth having different numbers of nuclei.
We take some well known species of paramecium like P. caudatum , P. aurelia, and P. multimicronucleatum. As we already discuss above that P. caudatum has two types of nuclei one is macronucleus and the second one is micronucleus. Besides the macronucleus, Paramecium aurelia has two micronucleus. Whereas, Paramecium multimicronucleatum has many nuclei range form 3 to 4 nuclei in each cell of P. micromultinucleatum.
Contractile Vacuoles in the diagram of Paramecium
Paramecium has two contractile vacuoles are shown in the diagram of paramecium. Its positon is fixed in endoplasm. Each vacuoles lies near end the body, close to the dorsal or aboral surface. The P. caudatum, The diastolic anterior contractile vacuole is larger surrounded with 6 to 10 long systolic radial canals. Whereas, the systolic posterior contractile vacuoles also surrounded with 6 to 10 diastolic radial canals.
Food Vacuoles in the diagram of Paramecium
Food vacuoles are membranous storing pocket found in the endoplasm of a cell. They may vary in shape and size according to the nature of ingested food particles. Food vacuoles are non contractile and numerous in number, they have been recently termed as gastrioles by Vokovsky. They are moving in endoplasm for the digestion of food materials, the movement is called cyclosis. This process finally provide nutrition in Paramecium body.
Cytopyge in the diagram of Paramecium
Cytopyge (cyto- cell + pyge- rump) is a minute apparatus called cell anus, cytopyge or cytoproct. It is found near the posterior end of the body and helps to get ride of waste materials from the body (see fig. Movement of food Vacuoles during digestion of food in Paramecium). It is difficult to say that it is a permanent opening or temporary opening formed at the time of egestion.
if you want to read full notes of Paramecium click on this link – Paramecium: Classification, Habitat, Structure, Locomotion, Nutrition