Question

A slide under a microscope shows the following features:
1. Unicellularity
2. Well defined nucleus
3. Biflagellate
What would you identify it as?
A. Protozoan
B. Bacterium
C. Euglenoid
D. Dinoflagellate

Answer 1

A unicellular microorganism is also called a single-celled organism; these are the organism which is only made up of a single cell, unlike multicellular organism which is made up of several different cells. This falls under two categories- prokaryotes and eukaryotes. All prokaryotes are single-celled, that is they are unicellular and are classified into bacteria, unicellular algae, etc. the oldest form of life is the unicellular organisms.

Complete answer: Protozoan- These are a eukaryotic organism. They are often studied by zoologists but they are part of the microbial world because they are microscopic and unicellular. Many of the protozoa species move independently by any one of the three types of locomotor organelles: cilia, flagella, and pseudopodia.
Bacterium- Bacteria are prokaryotes. Three notable common traits of bacteria are no membrane, unicellular, and microscopic organisms. Not all prokaryotes are bacteria, few of them are archaea. Bacteria do not have membrane-bound organelles. They do not have a true nucleus, mitochondria, chloroplast, etc.
Euglenoid- many cells of euglenoids are spindle-shaped and they do not have cell walls or any other outer structure to cover the plasma membrane. Euglenoids have two flagella. In euglenoids, the reproduction is through mitotic cell division.
Dinoflagellate- These microorganisms are single-celled eukaryotes. This family consists of algae and dinoflagellates which are mostly marine planktons but they are also seen in freshwater. Many of them use photosynthesis or they are mixed, that is they make their food as well as prey.

Hence the correct option is D, Dinoflagellate.

Note: The features mentioned in the question match the Protista kingdom. This kingdom is single-celled eukaryotes. Protists are primarily aquatic. Protists being eukaryotes the cell body contains a well-defined nucleus and membrane-bound organelles. Most of the dinoflagellates have two flagella. One flagellum lies longitudinally and the other lies transversely in between the wall plates furrow.