A slide under microscope shows following features:
1. Unicellularity
2. Well defined nucleus
3. Biflagellate -one flagellum lying longitudinally and the other transversely.
What would you identify it as?
A. Protozoa
B. Bacterium
C. Euglenoid
D. Dinoflagellate

Hint:-
A microscope is an instrument used to observe those microscopic things which are not seen by
the naked eye. It is usually any cell of the body where we can clearly see the organelles present
inside. It may be unicellular organisms like yeast, amoeba, and can study their characters.

Complete step-by-step solution:-Unicellular organisms are those which are made up of a single cell. The bacteria come under this category. They can fall into the category of prokaryotes or eukaryotes.
-Prokaryotes are those which do not have a well-defined nucleus.
-Eukaryotes are those which have the presence of a well-defined nucleus.
-In the case of prokaryotes, the Genetic material is present in the cytoplasm whereas eukaryotes are present inside the nucleus. Prokaryotes use flagella for locomotion.
A. Protozoa -They come under Kingdom Protista. They are unicellular and heterotrophic in
nature. They are generally known as parasites that cause disease. They move using flagella
or cilia.
B. Bacterium-They belong to single-celled prokaryotes. They lack a nucleus and the genetic
material is present in the cytoplasm of the cell. They have the presence of a whip like
structure called flagella for the locomotion.
C. Euglenoid- They belong to the Kingdom Protista. They are unicellular and flagellated
organisms. The flagella of Euglenoids are of an unequal size which is located at the anterior
end of the cell.
D. Dinoflagellate- They belong to the Kingdom Protista. They are photosynthetic in nature.They have the presence of two flagella. The characteristic feature of Dinoflagellate is the arrangement of the flagellum.One flagellum lies in the longitudinal groove and the other flagellum lies within the transverse groove.
The correct answer is option D i.e. Dinoflagellate.It is a unicellular organism with a well-defined nucleus.They are biflagellate where one flagellum lies in the longitudinal groove and the other flagellum lies within the transverse groove.

Note:-
-The kingdom Protista is classified into several groups, they are
- Protozoan Protists: they are animals like that are heterotrophs.
-They include protozoa that are parasitic in nature.
-Photosynthetic protists: they are plants that are photosynthetically active in
nature. They contain Dinoflagellates, Diatoms, Euglenoids.
-Slime mold- these are fungi like Protists. They have the character of both
Protozoa and Fungi.