How Do Protozoans Obtain Their Nutrition?
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Nature encompasses alluring, enchanting organisms one can think. These creatures may range from smallest protozoans to largest mammals. All the creatures require food for getting energy. The method of capturing food differs in different group of taxa. The way in which the protozoans devour their prey is also magnificent. The mechanism of getting nutrition is also amazing. Nutrition is a process of taking food in and digesting it and assimilating it to obtain energy. The ways in which the protozoans obtain their nourishment also varies drastically. They represent almost every type of nutrition. They may be holozoic, holophytic, parasitic, coprozoic, mixotrophic, saprozoic.
1. Holozoic Nutrition
The majority of Protozoans nourish themselves in the manner as the higher organisms did. They are able to feed on various micro-organisms, rotifers, crustaceans, other protozoans etc. Such protozoans are termed as Holozoic. They may be carnivorous, herbivorous, omnivorous or scavangerous. Holozoic nutrtion is also termed as zootrophic nutrition. This type of nutrition involves three basic steps:
A. Food Capture and ingestion
The regular method of food intake is also termed as phagocytosis, which differs greatly in different classes of protozoa. The locomotory organelles play an important role in food capture and ingestion. Rhumbler has defined four methods in which the locomotory organelles participate in food capture and ingestion.
a. Circumvallation
This method is very common Amoeba. Here the prey is surrounded by the locomotory organelle termed as pseudopodia from all the sides without coming in direct contact with the prey and a cup is formed. The food cup is later on completed by forming a food vacuole enclosing the prey with large amount of water.
b. Circumfluence
This method is aided by the locomotory organelles termed as axopodia and reticulopodia for capturing an immobile prey. A food cup is formed by direct contact with the prey and cytoplasm flows around the prey for engulfing it.
c. Invagination
In this case, the prey is first killed by a toxin secreted by the pseudopodia and then it is enclosed in the form of a food vacuole along with cytoplasm.
d. Import
In this case, the passive prey like the filamentous alga is simply drawn into the body upon contact and ingested. The general body surface plays an important role in this process.
B. Digestion and Assimilation
Digestion is always intracellular. The food vacuole is surrounded by a film. Acids, alkalies and enzymes are poured over the food to ensure digestion. The reaction is first acidic then alkaline. The prey is killed in the acidic environment which lasts for 4-60 minutes. Digestion mostly occurs in the alkaline phase. The digestive enzymes are aided by the lysosomes. Protein splitting proteases and starch splitting amylases are of wide occurrence. The presence of fat splitting lipase is controversial.
C. Egestion
In naked forms like Amoeba, the undigested matter goes out from the hinder part of the body. In some ciliates egestion occurs through a permanent opening present at the posterior end of the body termed as cytopyge.
2. Holophytic Nutrition
This mode of nutrition is also termed as autotrophic nutrition. This is very common in chlorophyll bearing flagellates. These organisms carry out photosynthesis with the help of carbon dioxide, water and chlorophyll. The oxygen is liberated and the left carbon is used for making food. The starch is stored in the form of amylum but in Euglena it is stored in the form of paramylum which is not colored blue with iodine. Certain protozoans house symbiotic green alga that carry out photosynthesis and provides food to them.
3. Saprozoic Nutrition
This mode of nutrition is also termed as osmotrophy. Here the flagellates that are in direct contact with the organic matter of the decomposed plants and animals obtain their nourishment. They obtain their food in the form of dissolved material.
4. Pinocytosis
This is also termed as cell drinking.It was first studied by Mast and Doyle in 1934 in Amoeba proteus. Pinocytotic channels are formed in the body for absorbing liquid food from the surrounding medium. This method helps the organism in getting higher molecular compounds from the surrounding medium.
5. Parasitic Nutrition
The Sporozoans are completely parasitic and obtain their nourishment by living as parasites in the body of other animals. They fall under two categories:
a. Commensals
They feed on the raw or digested material of the host in saprozoic manner. They are harmless endocommensals. E.g., Nyctotherus, Balantidium
b. Pathogenic
About 26 species of protozoa are known to be parasitic to humans. They are responsible for causing dreadful diseases like Sleeping sickness, Malaria etc.
6. Coprozoic Nutrition
Many free living Protozoans feed on the faecal matter of other animals and are termed as coprozoic. Eg., Cercomonas etc.
7. Mixotrophic Nutrition
Several Protozoans are able to get their nutrition in more than one way. Euglena gracilis is able to take nutrition both holophytically as well as saprozoically.
Whatever may be means of devouring food all leads to adaptation to colossal environment.
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