How does Paramecium obtain its food? – (Nutrition in Paramecium)

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A labeled diagram of Paramecium
A labeled diagram of Paramecium

Introduction To Nutrition In Paramecium

Paramecium is aquatic in nature. They can be seen widely in freshwater ponds, lakes, ditches, pools, streams, lakes, reservoirs, etc. where there is an availability of a great deal of decaying organic matter.

They are holozoic in nutrition meaning that they can ingest food particles and can later perform the internal processing of the gaseous, liquids, or solid food particles inside their cell.

When the Paramecium gets near to its food, its fast and rapid beating of cilia pushes the food like bacteria, yeast, etc. into its vestibule.

This food is then taken inside the cell through the cytostome (cell mouth) by phagocytosis. Later on, the food particle gets inside the water vacuole turning it into a food vacuole, sooner or later, digestion, absorption, and assimilation occur.

It is usually abundant in those waters which contain a great deal of decaying organic matter. The food of Paramecium consists of bacteria, yeasts, algae, and small protozoa that generally habitats those water bodies with decaying organic matter in it.

There are two important organs present externally in the Paramecium’s body that helps it in feeding. These are the numerous cilia, and the oral groove (vestibule).

The cilia during the swim of the organism, sweep and push the food particles into the oral groove which later gets ingested through the cytostome into the cytopharynx. You’ll know more about it in detail below so, keep reading.

Internally the Paramecium has numerous food vacuoles that contain the digestive enzymes needed to digest the food particles inside the cell.

How does Paramecium obtain its food? Nutrition in Paramecium takes place by 5 steps

  1. Selection of Food: It is the process through which the Paramecium will choose and select the food to feed on by responding to the various stimuli in the environment.
  2. Ingestion of Food: It is the process through which the Paramecium will intake the food within its food vacuole in the cell through phagocytosis and ciliary movements.
  3. Digestion of Food: It is the process through which the Paramecium will kill and break down the intaken food by various enzymatic actions inside the food vacuole.
  4. Absorption & Assimilation of Food: It is the process through which the Paramecium will absorb the various nutrients from the food and will utilize it for its various cellular metabolic uses.
  5. Egestion of Food: It is the process through which the Paramecium will egest or take out the undigested parts of the food from the food vacuole and then will eliminate it completely out of the cell.

Let’s understand each of these steps in detail…

1. Selection of Food: How does Paramecium select the food to feed on?

An organism must know what it will feed on, and so does the Paramecium.

Paramecium finds its prey by identifying the various nutritious from the innutritious food particles in its environment by the induction of a condition analogous to a conditioned reflex.

They better know that they need to feed in a holozoic manner, the same as that of Amoeba. The food consists chiefly of bacteria, some small protozoa, algae, diatoms, yeast, etc.

As the Paramecium moves and swims in water, it comes across various food particles that it can easily feed on. This interaction creates a conditioned reflex that allows the ingestion of that food particle to better take place with ease.

It has been seen that it will highly reject most of the large, non-digestible, and innutritious materials, and can only ingest certain kinds of food.

This rejection and ingestion mechanism of the food is highly stimulated by the response created from the various conditioned reflex.

They can intake food very rapidly and quickly. It has been estimated that a single Paramecium can ingest bacteria like Bacillus coli at the rate of 2 to 2.5 million individuals per 24 hours.

Their common form of prey is actually bacteria. In general, a single organism has the ability to eat around a minimum of 4,000 to 6,000 bacteria a day.

Paramecium can also ingest various food particles like bacteria, algae, etc. to stay in a specific symbiont association with it, in which both organisms are benefited.

  • For example: The gram-negative bacterium Holospora obtusa is a macronucleus-specific symbiont of the ciliate Paramecium caudatum. This bacterium is known to enter the host cell by invading the food vacuole and overall infecting its macronucleus while growing exclusively in the nucleus. Holospora obtusa contributes to the heat-shock resistance in Paramecium caudatum.
  • For example: The algae Zoochlorella is an endoplasm-specific symbiont of the ciliate Paramecium bursaria. These algae help the Paramecium to live holophytically for long periods on the food substances manufactured by the algae. During its scarcity of food, it can digest its own Zoochlorella and can live apparently and independently without them.

2. Ingestion of Food: How does Paramecium ingest the food?

We have learned about the movement and locomotion of Paramecium and how it uses its cilia for feeding and locomotion.

Unlike the other protozoans like Amoeba and Euglena, Paramecium has a more systemic and a bit complex mechanism to intake the food it needs.

Its food-catching apparatus that is present in the vestibule is much more complex than the other protozoans. Its food-catching apparatus has numerous ciliary bands along with the cytostome.

The junction where the ciliary bands end at the cytostome region is the buccal cavity part of the Paramecium.

Paramecium swims to places where it can get its food. When the Paramecium locomotes in water using the various ciliary movements arranged on its out pellicle, it pushes the food particle towards its vestibule.

Ciliary bands of the vestibule direct the food particles into the buccal cavity. As the food particles reach the buccal cavity, the food gets gradually collected at the bottom of the cytopharynx.

There, from the inner part of the cytopharynx, a water vacuole always remain present to intake or ingest the food particles into a membraneous vesicle thus turning it into a food vacuole.

Various food vacuoles can be formed from the water vacuoles depending on the rate of supply of food and the rate of feeding.

It has been seen that when the cilia beat and the various food particles start to collect in the vestibule then, only the selected food particles get driven into the food vacuole and this is known as the selection path.

On the other hand when the unwanted food particles are driven outside of the vestibule then, it is known as the rejection path.

3. Digestion of Food: How does Paramecium digest the food?

Digestion of food in Paramecium occurs as soon as the food gets ingested inside the cell.

All of the digestion in Paramecium takes place inside the food vacuoles only. It’s like the gut of higher animals but at the cellular level.

Once the food vacuole is formed completely, it starts to circulate inside the body of the Paramecium. Each food vacuole consists of various food particles being surrounded by a thin film of water.

There may be various food vacuoles and each of the food vacuoles is circulated along a more or less definite path by a slow streaming movement of the endoplasm and this slow streaming movement is also termed as cyclosis.

These food vacuoles represent a number of spherical, small, and large vesicles inside the cytoplasm. These food vesicles contain water and food in various stages of digestion.

Several vacuoles may be well-seen circulating inside the Paramecium in a definite direction. The circulating motion follows the movement of food vacuoles first posteriorly, then forward, and aborally, and again posteriorly, and then orally up to the anal orifice (cytopyge) inside the Paramecium’s body.

The food vacuoles contain lysosomes that contain the various digestive enzymes that help in the digestion of the trapped food particle slowly and eventually.

During the digestion process, the reaction inside the food vacuole is first acidic and then alkaline.

When the food vacuole is acidic, the organism that is trapped inside gets killed due to the high pH effect.

And when the food vacuole is alkaline, the digestion of starch, fats, proteins, carbohydrates, etc. takes place from that dead food particle by the enzymes amylase, protease, lipase, etc.

4. Absorption & Assimilation of Food: How absorption and assimilation occur in Paramecium?

Absorption is the process of absorbing nutrients like proteins, lipids, starch, etc. from the digested food material into the cytoplasm leaving behind the undigested food material in the food vacuole of Paramecium.

Assimilation is the process of obtaining energy from the absorbed food nutrients and make its use in the body. In Paramecium, absorbed food molecules are utilized for producing the energy required to carry out different life processes within the cell.

Both absorption and assimilation take place during the circulation of the food vacuole by cyclosis inside the organism.

If the Paramecium ingests and digests enough food nutrients then the excess food gets stored in the form of glycogen as well as lipids as a reservoir of future energy.

The post-digestion products like the glycogen and fat globules most probably are diffused into the surrounding cytoplasm and either stored and used for vital activity and cell growth. The fat globules are also used as the storehouse of cellular energy.

Absorption of nutrients takes place in each and every part of the cytoplasm as the food vacuoles due to its ability of cyclosis keep on moving in the endoplasm.

The total completion of digestion and the absorption can take about 28-32 hours.

5. Egestion of Food: How does egestion occur in Paramecium?

Now, what actually happens after absorption and assimilation? After the absorption of food, the food vacuole shrinks in size.

The food vacuole gradually becomes smaller in size and shape as the digestion and absorption proceed.

Finally, as it keeps on shrinking, the undigested residual matter is eliminated from the body, through a definite anal spot which is also known as the cytopyge that is present on the ventral surface, posterior to the cytostome.

The cytopyge resembles that of the cells anal as all the undigested food particles coming out from the food vacuole go out through this cellular pore to the outside water.

As soon as the food vacuole gets devoid of the food particles it becomes the water vacuole which again repositions itself at the base of the cytostome to again collect the ingested food particles and turn into a food vacuole. This cycle repeats again and again during the lifetime of the Paramecium.

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