Question

Why are protozoans placed in kingdom protista and not in kingdom animalia ?
A. Protozoans have an autotrophic mode of nutrition.
B. Protozoans are unicellular and have heterotrophic mode of nutrition.
C. Both A and B
D. None of above

Answer 1

Protozoa is an informal term for a group of single-celled eukaryotes, either free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and debris.

Complete Answer:
Let us analyse the options for finding the correct answer.

Option A: Protozoans have autotrophic mode of nutrition, i.e. they cannot synthesize their own food. Therefore, this is the incorrect option. They generally feed on organic matter such as organic tissues, debris and also on small microscopic organisms.

Option B: Protozoa are eukaryotic, unicellular and heterotrophic organisms. They are either found as parasites or are free - living. Therefore, this is the correct option.

They are heterotrophs, i.e. they cannot produce their own food and they have holozoic mode of nutrition. Their mode of ingestion is via phagocytosis. The food is captured with the help of pseudopodia and is transported to the food vacuole. The ingested food is then acted upon by lysosomal enzymes and the digested food is distributed throughout the cell.

Thus, the correct option is B) Protozoans are unicellular and have heterotrophic mode of nutrition.

Note: Protozoa also contain a number of parasites which are known to cause several diseases. Few examples are,
i. Plasmodium - It is a malarial parasite
ii. Trichomonas - It causes trichomoniasis
iii. Trypanosoma - It causes sleeping sickness