Paramecium feeds in a holozoic manner, like an amoeba.
The food comprises chiefly bacteria and minute protozoa which floats in the water in which it lives.
It also feeds unicellular plants (algae, diatoms, yeasts, etc.) and small bits of animals and vegetables.
Paramecium swims to a place where it can get its food. It does not move while feeding.
The available data suggest that 2 to 5.5 million individuals of Bacilluscoli are devoured by a single paramecium in 24 hrs.
Paramecium will reject most of the non-digestible materials and devour certain kinds of food.
One species, P. bursaria is interesting, being green in color due to the presence of numerous algae, the symbiotic Zoochlorella in its endoplasm. Thus, it can live holophytically for long period on the food manufactured by this alga. During, the scarcity of food, it can digest even its own algae and can live apparently independently without them.
2. Feeding mechanism
Paramecium swims to places where it can get its food.
Its food catching apparatus is much more specialized than that of Amoeba and Euglena.
When it enters a region of abundant food, it comes to rest.
It feeds only at rest or when swimming very slowly, it never feeds when swimming fast.
Food is ingested by the cytostome lying at the bottom of the buccal cavity.
The constant lashing of cilia of the oral groove drives a current of water with food particles toward the vestibule.
From the vestibule, some food particles are rejected and thrown out, but others pass into the cytostome.
Passage along with ciliary action drives selected food particles, which is termed the selection path.
Whereas passage along which unwanted food particles are driven outside a vestibule is the rejection path.
Ciliary tracts of the vestibule direct the food particles into the buccal cavity.
The beating of cilia of membranelles of the buccal cavity drives the selected food particles through the cytostome into the cytopharynx or cell gullet.
The quadrulus and peniculi control the passage of food into the food vacuole which is formed laterally.
The food now gradually collects at the bottom of the cytopharynx into a membranous vesicle which is later released off as food vacuole.
The quadrulus and peniculi control the passage of food into the food vacuole.
The vacuole contains some water beside food.
Rapid and irregular movement of endoplasm does not occur in paramecium.
The food vacuole is circulated around the body along a more or less definite path by a slow rotatory streaming movement of endoplasm called cyclosis.
In well-fed paramecium, several food vacuoles may be seen circulating in a definite direction in the endoplasm.
The food vacuoles are carried1st posteriorly, then forward and aborally and gain posteriorly and orally up to cytopyge.
Digestion and assimilation of food take place during this journey.
Digestion takes place with the help of certain enzymes (proteases, carbohydrase’s, lipases) secreted by protoplasm into the food vacuoles.
As in Amoeba, the contents of vacuole first become acidic (pH about 4) and then become alkaline.
The major digestion of food occurs during the alkaline phase.
In digestion, proteins are converted into amino acids, carbohydrates into soluble sugar, and glycogen and fats are probably also digested.
Products of digestion are diffused into the surrounding cytoplasm and either stored or used for vital activity and growth.
The food vacuole becomes smaller as digestion and absorption proceed.
Finally, the undigested food materials are eliminated from the body through an anal spot or cytoproct on the ventral surface posterior to the cytostome.
The cytopyge is of the nature of a potential cell anus as the undigested matter is always discharged at this spot.
References and Sources
Kotpal RL. 2017. Modern Text Book of Zoology- Invertebrates. 11th Edition. Rastogi Publications.
Jordan EL and Verma PS. 2018. Invertebrate Zoology. 14th Edition. S Chand Publishing.