In the pictures below,
identify the arrowed reproductive structures of microscopic cyanobacteria
based on the following descriptions:
Akinetes
are dormant structures larger than the vegetative cells, are rich in food reserves, and have thick walls. Most filamentous cyanobacteria develop akinetes in adverse conditions (e.g., winter, dry periods). When favorable conditions return, they germinate and produce new filaments.
Hormogonia
are short pieces of filaments consisting of 5–15 trichomes that fragment and develop into new filaments.
Heterocytes
(or heterocysts) are multicellular structures that have a thick and massive sheath, formed by members of the Nostocales. It is the location of the enzyme nitrogenase for nitrogen fixation, the conversion of nitrogen gas into ammonium and then amino acids. They may be intercalary or terminal in position and may germinate from either end or both the ends to give rise to new filaments.
Non-filamentous cyanobacteria generally produce spores such as endospores, exospores and nanocysts which contribute by germinating and giving rise to new vegetative cells in favorable conditions.
Endospores
are produced endogenously like those in bacteria;
exospores
are the result of exogenous budding of cells, and the
nanocysts
are produced endogenously like endospores. The difference between an endospore and a nanocyst is that in endospore formation, the parent cell simultaneously enlarges in size, whereas in nanocyst formation, there is no such enlargement of the cell.
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