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Term Paper on Paramecium
Term Paper Contents:
- Term Paper on the Habits and Habitat of Paramecium
- Term Paper on the Culture and Locomotion of Paramecium
- Term Paper on the Nutrition of Paramecium
- Term Paper on the Respiration and Excretion of Paramecium
- Term Paper on the Behaviour of Paramecium
Term Paper # 1. Habits and Habitat of Paramecium:
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Paramecium is a typical ciliate Protozoa. Ciliates are characterized by the presence of cilia as locomotor organelle, nuclear dimorphism and a unique type of sexual reproduction called conjugation. The two types of nuclei are morphologically and physiologically distinct from one another, these are macronucleus and micronucleus.
It is commonly found in fresh water 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. It is free living organism and this species is worldwide in distribution.
Term Paper # 2. Culture and Locomotion of Paramecium:
Culture:
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If submerged weeds from a pond are placed in a jar of distilled water, swarms of Paramecia will develop after some time. To make a pure culture, water containing hay is boiled, decant the water and add a few grains of wheat. The water becomes turbid with a large number of bacteria. Now transfer a few Paramecia into this culture from the first jar. This culture of Paramecia will get abundant food in bacteria and will flourish well.
Locomotion:
Paramecium performs locomotion by two methods, viz., metaboly or body contortions and by cilia.
Ciliary locomotions are the main mode of movement. The cilia can beat in forward and backward direction and so can the animal itself. The stream-lined body facilitates the swimming of the animal. The animal can move with a speed of 1500 or more µ/sec. The collaborative action of cilia causes the organism to swim or to maintain a current of fluid over the ciliated surface.
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The beat of the cilium may be separated into two phases namely the effective stroke and the recovery stroke. During the effective stroke or the strong backward lash, the cilium becomes slightly curved and rigid and strikes the water like an oar so that the body is propelled forwards in the opposite direction of the stroke. The recovery stroke follows the effective stroke and brings back the cilium into position for the next effective stroke.
The cilia during movement do not move simultaneously and independently but progressively in a wave-like manner called metachronal rhythm. Cilia of the same transverse row beat together and those of the same longitudinal row beat one after the other from anterior to the posterior end.
During the forward movement, the metachronal waves pass from the posterior and forwards. However, the animal does not take a straight tract but rotates spirally like a rifle bullet. This is brought about mainly as the cilia do not beat directly backwards but obliquely towards right so that the animal rotates to the left on its axis.
Moreover, the cilia of the oral groove strike obliquely and more vigorously so as to turn the anterior and continually away from the oral side and move in circle. Nevertheless, the combined effect causes the movement almost along straight path, rotating about is axis in an anticlockwise direction.
According to Jennings the spiralling of paramecium is due to the fact that while cilia strike chiefly backward they do so obliquely to the right thereby causing the animal to roll over to the left. Also this swerving of the body toward the aboral surface is due largely to the greater power of the effective stroke of the oral cilia which strike more directly backward. The rotation of paramecium on its long axis thereby enables the Paramecium to follow a more or less straight course in forming large spirals.
Paramecium can execute considerable contracting and twisting movements, in squeezing through tangled masses of minute water weeds, through small apertures, and through other passages, which are smaller than its diameter. These movements are caused by the contractions of myonemes present in the ectoplasm. But on its exit from the passage the body soon restores the normal shape due to the elasticity of the pellicle.
Term Paper # 3. Nutrition of Paramecium:
The nutrition of Paramecium is holozoic. It feels mainly upon bacteria, which abound in water in which it lives, although it may also feed upon small protozoans, algae and yeast. While actively feeding, the paramecia move rather slowly. Food is taken in only at a definite place on the surface, the cell-mouth, situated at the bottom of the vestibulum.
The oral groove is provided with relatively larger cilia which are arranged in definite tracts and direct the food down to the mouth. As the food particles are driven in by ciliary action all sorts of particles from the neighbourhood reach the vestibulum. From here only smaller particles of one particular size move in.
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Thus, a selection of smaller particles takes place. Other particles finally pass out. These ciliary tracts were formerly called the undulating membranes. The food particles (bacteria) are whirled around by the special ciliary tracts and are concentrated into balls at the bottom of food tracts. The finished ball then passes into the endoplasm as a food vacuole. The food vacuoles are formed in about 1-5 minutes depending upon the abundance of material.
The vacuole contains some water besides the food. Rotary streaming movements of endoplasm called cyclosis carry the food vacuoles along a definite course which is functionally equivalent to a digestive tract. The tract begins from the end of the cytopharynx, then to the posterior side and then forwards to circulate with the endoplasm, then to the dorsal surface, then towards the anterior end, then downwards to the cytopyge. Early on its journey the food vacuole decreases in size then increases again.
In digestion proteins are changed into amino acids, carbohydrates into soluble sugars and glycogen, and fats are probably also digested. The content of food vacuoles are a first acidic (pH about 4) and then become alkaline, major digestion occurs during the alkaline phase. The undigested matter is egested through the cytopyge with some force.
Formation of Food Vacuoles:
The movements of the ciliary bands (endoral membrane, quadrulus and peniculi) lining the buccal cavity drive the selected food particles through the basal mouth or cytosome into the narrow cell gullet or cytopharynx. The particles gradually accumulate at the inner or posterior end of the cytopharynx, which opens into the endoplasm. Here they form a rounded or ball-like mass, the food vacuole.
It grows rapidly and then becomes nipped off or breaks free, while another food vacuole begins to form in its place. The mechanism by which the food vacuole is liberated is not properly known. Probably the post-buccal fibres or pharyngeal cilia help in this process. A food vacuole required 1 to 5 minutes to form depending on food supply and feeding rate.
Cyclosis:
The food vacuole forms in the endoplasm and consists of food particles surrounded by a thin film of water. It is circulated around the body along a more or less definite course by a low streaming movement of the endoplasm known as cyclosis. Several vacuoles may be seen thus circulating in a definite direction in the endoplasm of a well-fed Paramecium. The newly detached vacuoles are carried first posteriorly, then forward and aborally and again posteriorly and orally up to the cytopyge.
The permanence of path travelled by the vacuole during cyclosis raised this question in the mind of workers that there existed a performed digestive tract in the endoplasm. This view is also supported by the fact that other components of the endoplasm retain their fixed position and do not circulate like the food vacuoles. Later Dogiel confirmed this hypothesis.
Cyclosis can be demonstrated experimentally, if milk stained with Congo red is fed to Paramecium, the fat globules of milk in the food vacuoles will first turn red due to acidic reaction of enzymes, then they will change from shades of purple to blue due to alkaline reaction, the vacuoles will show the course of cyclosis.
Term Paper # 4. Respiration and Excretion of Paramecium:
Respiration takes place by diffusion through the surface and is essentially the same as in all other animals, i.e., oxygen is taken and used for the burning of food; and carbon dioxide, water and nitrogenous wastes are given off. Some authors consider the contractile vacuole to be respiratory structure.
Oxygen needed for respiration is obtained from water that enters the body and reaches the contractile vacuole and carbon dioxide is removed by the latter. The pellicle is also believed to play some part in respiration for most of the oxygen enters through it. Active paramecia utilize most oxygen that is why the rate of oxygen consumption in a freshly mask culture containing older non-dividing paramecia.
If the temperature is increased the rate of respiration is markedly accelerated. It is a fact that, like all other organisms paramecia require oxygen to carry on the functions of life. It is not surprising therefore, to see paramecia gather at the surface of the culture media where the oxygen concentration is maximum. If oxygen is removed completely from the medium in which paramecia live they will die in twelve hours.
Waste products of cellular metabolism are eliminated from the protoplasm by diffusion. Such waste products usually include nitrogenous substances only. The other mostly widely accepted view held today with regard to the removal of nitrogenous wastes is that they are eliminated by the contractile vacuoles, which are primarily organelles for the removal of excess of water (osmoregulation).
As the water from the environment enters the cytoplasm it becomes laden with nitrogenous waste products of metabolism that are excreted through the contractile vacuole. Excretion also functions in order to maintain osmotic equilibrium.
The cytoplasm of paramecia contains crystals and crystalline granules. They are carbolic products of metabolism. They are first dissolved and then got rid of with the water of the contractile vacuole. How the insoluble crystals such as those of calcium phosphate are got rid of is not known yet.
Osmoregulation:
The primary function of the contractile vacuoles is osmoregulation i.e., to regulate the water content of the body and remove the excess of water. Due to higher concentration of the protoplasm of paramecium, there is continuous inflow of water from the surrounding water by endosmosis. Some water is also absorbed during ingestion of food.
The excess of water is removed through the radial canals which radiate from the contractile vacuole. This is finally passed into the two contractile vacuoles which contract (systole) and expand (diastole) at regular intervals assisted by the contractility of the myofibrils.
When the vacuoles have swelled to a certain size, it contracts and discharges the excess of water along with nitrogenous wastes such as urea and ammonia through the pore in the pellicle. The vacuoles contract alternately at the interval of 10-20 seconds. The posterior vacuole pulsates faster than the anterior vacuole because larger amount of water is delivered into the posterior region by the cytopharynx.
Term Paper # 5. Behaviour of Paramecium:
The responses of Paramecium to various kinds of stimuli are learned by study of its reactions and of the grouping or scattering of individuals in a culture. The response is positive if the animal moves toward a stimulus and negative when it moves away. To an adverse stimulus the animal continues to give the avoiding reaction until it escapes.
In avoiding reaction the ciliary bear reverses, the animal moves backward a short distance and then rotates in a conical path by swerving the anterior end aborally while pivoting on the posterior tip. All adjustments are made by trial and error. Experiments have shown that the anterior end of the animal is more sensitive than the other parts.
The responses of paramecium to different stimuli may be grouped as follows:
i. Reaction to Mechanical Stimuli (Thigmotropism):
If a moving paramecium strikes a solid object, a strong avoiding reaction occurs. It moves back by reversing the direction of cilia and turns on its side and again swims forward. If it again comes in contact with the object, it repeats the same process and continues till it reaches the safe zone.
Paramecium is known to learn by trial and error reaction. If the animal reaches an unfavourable area, it gives the avoiding reaction. It also constantly tests the water which enters the oral groove in the form of a come. If there is an irritating chemical in the water ahead or if the temperature of the water is not agreeable, the animal shows avoiding reaction, it immediately backs up and pivots upon its posterior end while the anterior end swings in a circle.
Again it swims forward but in a different direction. This process is repeated till it comes in the safer zone. This reaction is known as trial and error method as by frequent trials and errors, it is able to choose the right direction.
ii. Reaction to Chemicals (Chemotaxis):
Generally Paramecia respond to chemical stimuli by means of avoiding reaction. If a drop of weak salt solution (0.5 per cent) is introduced in a Paramecium population on a micro-slide, the animals respond with the avoiding reaction and none enters the drop. To acids, however, the response is positive even when the concentration is of sufficient strength of kill them.
iii. Reaction of Light (Phototaxis):
With the exception of green Paramecium bacteria which are positively phototactic other species slow no reaction to ordinary light. However, if the intensity of light is suddenly increased, they behave negatively. They also behave negatively to darkness and ultraviolet rays.
iv. Reaction to Gravity (Geotaxis):
The paramecia behave negatively to the force of gravity and keep on swimming upwards with their anterior ends directed away from the force of gravity. It may are introduced in an inverted water filled U-tube, they immediately move upward into the horizontal part of the tube.
v. Reactions to Electric Current (Galvonotaxis):
Paramecia respond to electric stimuli. When two electrodes are placed opposite each other in a shallow dish containing Paramecia and a constant current applied, all the organisms swim in the same direction toward the cathode or negative electrode where they concentrate in large numbers. If the direction of the electric current is reversed while the Paramecia are swimming towards the cathode, the organisms reverse the direction and swim towards the new cathode.
vi. Reaction to Water Current (Rheotaxis):
Paramecia show a positive rheotaxis. In gentle water current the Paramecia will mostly move with the flow with their anterior ends upstream.