Biology Question on biological classification

Question

A special cell called heterocyst is found in

Answer 1

Solution

Heterocyst is a large-sized pale coloured thick-walled cell which occurs in terminal, intercalary or lateral position in filamentous cyanobacteria (BGA), e.g., Nostoc. The thick wall is impermeable to oxygen but permeable to nitrogen. Thylakoids lack phycobilisomes. In the absence of phycobilins (which are principle light absorbing pigments in oxygen evolving photosynthetic reactions) and chlorophyll a there is no $CO_2$ fixation or $O_2$ productions in heterocysts. Heterocyst is dependent for its nourishment on adjacent vegetative cells.