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Heterocysts (also called heterocytes) are specialized nitrogen-fixing cells produced by certain filamentous cyanobacteria—such as Nostoc, Cylindrospermum, and Anabaena—when environmental nitrogen is limited. They house the enzyme nitrogenase, which converts atmospheric N2 into a usable nitrogen form for the filament. Since nitrogenase is deactivated by oxygen, heterocysts create a microanaerobic interior. Their formation involves extensive changes in gene expression and cell structure. Heterocysts: add three extra cell-wall layers, including a glycolipid layer that restricts oxygen and CO2 entry synthesize nitrogenase and other nitrogen-fixation proteins dismantle photosystem II (the oxygen-evolving complex) upregulate glycolytic enzymes produce proteins that scavenge residual oxygen form polar cyanophycin plugs that slow diffusion between cells Because heterocysts lack the water-splitting photosystem II, they cannot carry out typical photosynthesis; ...

Delhi's Indira Gandhi International Airport faced severe disruption Friday as an Automatic Message Switching System (AMSS) glitch caused over 300 flight delays. Air traffic controllers were forced to revert to manual procedures, drastically slowing operations and creating mounting backlogs at India's busiest aviation hub. What Failed: Critical System Breakdown The crisis began when the Automatic Message Switching System (AMSS) —responsible for transmitting flight plan data to controller screens—crashed. This forced air traffic controllers to process all information manually, severely delaying arrivals and departures. System Impact: AMSS handles high-volume flight plans, weather updates, and operational notices Manual Fallback: Controllers resorted to hand-written logs and voice coordination Timeline: Issues began Wednesday evening; major disruption started Thursday 3 PM Scale of Disruption IGIA typically manages 1,500 daily aircraft movement...