Question

Which one is not a free-living Protozoa?
a. Amoeba
b. Euglena
c. Giardia
d. Noctiluca

Answer 1

Protozoans are a group of unicellular eukaryotes, these organisms are present as either free-living forms or as parasites, and these protozoans mainly feed on organic matter such as other microorganisms, or any other organic debris.

Complete answer:
- The size of the protozoans ranges from 1 micrometer to several millimeters.
- The organisms of the protozoans are present either as free-living or some other live as parasitic or symbiotic forms.
- The free-living protozoans are mostly seen in freshwater, saltwater, and other moist environments.
- Whereas some are life as symbiotic forms, either in vertebrates or invertebrates or in plants, where both host and protozoa are benefited from each other.
- When coming to parasitic forms, where they live and feed on the host and in return they harm the host.
- When coming to the feeding habits, all protozoans are heterotrophs, where they depend on other organisms for their food, and they consume the food, by ingesting the whole or by absorbing small debris, for example amoeba obtain food by pseudopodia, and some aquatic protozoans feed by osmotrophy and some other organisms as Parasites they feed on host mainly by Phagocytosis, and some parasites like Plasmodium fed on the blood cells by phagocytosis(pinocytosis) when it is in trophozoite form.
- They have different locomotory organs to move, like flagella, cilia, pseudopodia, etc.
From the above-given options, amoeba Proteus is free-living, Euglena are also free-living organisms, and Noctiluca is also a free-living organism. But Giardia is a parasitic form, and it causes a disease called giardiasis. So the answer is Giardia.

Hence, the correct answer is option (C).

Note: Some protozoans are Mixotrophic, where they show both autotrophy and heterotrophy, some protozoans live photosynthetic algae, where they grow and obtain nutrition and some organisms steal the chloroplast from the host, and maintain them in their own body and obtain nutrition by photosynthesis, example is Mesodinium rubrum.