Question

'Red tide' is caused by?
A.Gonyaulax
B.Ceratium
C.Taceratium
D.All of these

Answer 1

Hint: Some microscopic algae mainly Dinoflagellates show explosive growth and accumulation in water bodies which results in the formation of algal bloom which is called Red tide. Many bioluminescent Dinoflagellates like Noctiluca, Gymnodinium, and Gonyaulax cause red tide due to explosive growth and accumulation in water bodies.

Complete answer:
Pyrrophyta are a group of photosynthetic protists." Pyro" means "fire" and phyta means "algae". So, Pyrrophyta is known as fire algae. Members of this group are unicellular, autotrophic biflagellates(bi means two and flagellate means flagella). Dinoflagellates are photosynthetic protists that come under group pyrrophyta.
Most of the Dinoflagellates are autotrophs, perform photosynthesis, and are free-living but some forms like zooxanthellae which is symbiotic means it is found in association with other protists or invertebrates, and the association is symbiotic that means both the organisms are benefited.
Dinoflagellates are also known as whorling whips because of the presence of transverse flagellum. When a transverse flagellum moves, the movement of this flagellum helps in the spinning of the cell and that is why they are known as whorling whips.
> Option-A-Gonyaulax: Gonyaulax is a Dinoflagellate and sometimes the number of these Dinoflagellates increases tremendously in the sea and that area of the sea appears little red because of the pigments they have that means they are responsible for Red tide. So, this is the correct option.
> Option-B-Ceratium: Ceratium is one of few Dinoflagellates which show sexual reproduction (Reproduction is by zygotic meiosis). Ceratium is not responsible for causing red tides. So, this option is incorrect.
> Option-C-Triceratium: Triceratium too is not responsible for causing red tides. So, this too is an incorrect option.
> Option-D-All of these: Since options B and C are incorrect, this option can't be correct.

So, the correct answer to this question is an option A."Gonyaulax".

Note:
Due to the presence of protein luciferin, Dinoflagellates exhibit the special property of bioluminescence or phosphorescence. Luciferin protein has a property to absorb wavelengths during the daytime or when light is available and emit wavelengths in dark. So they glow in the dark. That is why they are also known as Fire algae.