Question

In dinophyceae, sulcus is
 (A) Transverse flagellum
 (B) Longitudinal flagellum
 (C) Transverse groove
 (D) Longitudinal groove

Answer 1

Hint: Dinoflagellates are algae like single-celled eukaryotes which are the members of class Dinophyceae. They are unicellular, flagellated protists. They are mostly found in the marine environment however, some species are also in freshwater.

Complete step-by-step answer:
Most Dinoflagellates have two dissimilar flagella in their body plan i.e. Transverse and longitudinal flagellum. One flagellum which is flat, ribbon-like arises from the transverse groove called the cingulum, and the other flagellum which is long with distal ends free arises from a longitudinal groove called the sulcus.
A sulcus, longitudinal groove arises from the annulus to the point at which the longitudinal flagellum is attached.
So, the correct answer is (D) in dinophyceae, sulcus is the longitudinal groove:

Additional information: Some dinoflagellates are photosynthetic while most of them are mixotrophic. Many photosynthetic dinoflagellates contain chlorophyll a and c pigments. While many dinoflagellates lack photosynthetic pigments and are called heterotrophs. Many dinoflagellates show symbiotic association with organisms like sponges, corals, etc.
Dinoflagellates reproduce through asexual modes of reproduction by longitudinal cell division with each daughter containing a flagellum and a part the of wall or theca. Then, each daughter reconstructs the parts that are missing in their body. Though, sexual reproduction is also present but rarely.

Note: Dinophyceae are known to produce various toxins. Dinoflagellates like Gymnodinium catenatum and Alexandrium tamarense are known to release neurotoxins like saxitoxin causing paralytic shellfish poisoning. Gymnodinium breve releases toxins causing neurotoxic shellfish poisoning and leading to the formation of algal blooms. These on coming in contact with humans and other organisms causes health hazards.