The following points highlight the seven modes of nutrition in protists. The modes are: 1. Photosynthetic 2. Holozoic or Zoo-Trophic 3. Saprobic or Saprotrophic 4. Parasitic 5. Mixotrophic 6. Symbiotic 7. Pinocytosis.
Modes of Nutrition # 1. Photosynthetic (Holophytic):
In this mode, the organisms prepare their food from CO2 and water by utilizing sunlight with the help of photosynthetic pigments like chlorophyll. The process is called photosynthesis. Examples are din flagellates, diatoms and euglenoids.
Modes of Nutrition # 2. Holozoic or Zoo-Trophic (Ingestive, Phagotrophic):
In this mode, the individual captures and ingests the food like animals. It is found in many protozoans like Amoeba and Paramecium.
Modes of Nutrition # 3. Saprobic or Saprotrophic:
In this mode, the organism releases enzymes into the surroundings where the enzymes convert organic matter into simpler products. These products are then absorbed through body surface of the organism. Saprobic nutrition is found in slime moulds.
Modes of Nutrition # 4. Parasitic:
Some protists get their food from the body of other organisms. The individual which obtains its food is called parasite and the organism from which parasite gets food is called host. Trypanosoma, Giardia, Entamoeba, Plasmodium are some examples of parasites.
Modes of Nutrition # 5. Mixotrophic:
It is a mixed type in which the organism can perform two kinds of nutrition. For example, in Euglena nutrition is both holophytic and saprobic.
Modes of Nutrition # 6. Symbiotic:
Zoo flagellates Trichonympha and Lophomonas live as a symbiont in the intestine of termites and wood roaches respectively. Both Trichonympha and Lophomonas secrete cellulose digesting enzymes which convert cellulose into glucose. The digested food (glucose) is shared by both zoo flagellates and the hosts.
Modes of Nutrition # 7. Pinocytosis:
Soluble organic substances and salts are known to be absorbed in Amoeba and others through pinocytosis.