Oxygen dissolved in the surrounding water is taken in and carbon dioxide is excreted out by diffusion through general body surface. The dissolved oxygen which is taken in is used for oxidation of protoplasmic molecules.
The undigested matters of the food vacuoles are excreted through cytopyge. Waster products of the metabolism like urea, uric acid and other nitrogenous compounds diffuse out of the body through the general body surface because their concentration is always higher in the body. Also the crystals present in the body are excretory products which get dissolved and are eliminated with the fluid of contractile vacuole.
As paramecium lives in fresh water, it has the problem of water being transported into it because of osmosis. To ensure that the entry of too much water do not explode it away, contractile vacuoles are present. The contractile vacuoles help in regulating the osmosis and thus they help in the process of osmoregulation.
The main function of the contractile vacuoles present in the body of the Paramecium is osmoregulation. The concentration of the cytoplasm is higher than that of the surrounding water and this result in endosmosis. Water diffuses in through the semipermeable pellicle. Small quantity of water also enters along with the food. This excess water is collected and expelled out of the body by these two contractile vacuoles present at anterior and posterior end of the paramecium body.
The contractile vacuoles contract and expand at regular intervals. Excess of water from the cytoplasm is collected in the tubules of endoplasmic reticulum. From it water is passed on to the nephridial tubules which in turn are sent to collecting tubules of the radiating canals of the contractile vacuoles. The radiating canals collect the water in their ampulla. When the ampulla is filled up, the water is discharged into the contractile vacuole. The vacuoles expand by collecting water. When grown to its maximum size it contracts and expels water to outside through the discharge canal which opens outside through a pore in the pellicle.
Paramecium responds to various stimuli. It moves towards the beneficial stimulus which is called as positive reaction and moves away from the harmful stimulus which is called as negative stimulus.
Paramecium avoids too hot or too cold water. It also moves away from the area containing irritating chemicals in the water. It avoids strong light. A positive response is shown towards weak electric current.
1. Write about Excretion in Paramecium.
2. Explain the method of osmoregulation in Paramecium.
3. How does a Paramecium respong to the stimuli?
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