Question

Describe the various modes of nutrition in protists.

Answer 1

Protists have the following modes of nutrition:

1. Photosynthetic: In this mode, the organisms prepare their food from $C{O}_2$ and water by utilising sunlight with the help of photosynthetic pigments like chlorophyll. The process is called photosynthesis. Examples are dinoflagellates, diatoms and euglenoids.
2. Holozoic: In this mode, the individual captures and ingests the food like animals. It is found in many protozoans like Amoeba and Paramecium.
3. Saprobic: In this mode, the organism releases enzymes into 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.
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.
5. Mixotrophic: It is mixed type in which the organism can perform two kinds of nutrition. For example, in Euglena nutrition is both holophytic and saprobic.
6. Symbiotic: Zooflagellates Trichonympha and Lophomonas live as symbiont in the intestine of termites and wood roaches respectively. Both Trichonympha and Lophomonas secrete cellulose digestive enzymes which convert celulose into glucose. The digested food (glucose) is shared by both zooflagellates and the hosts.
7. Pinocytosis: Soluble organic substances and salts are known to be absorbed in Amoeba and others through through pinocytosis.