Cyanobacteria
சயனோபாக்டீரியா
Do not confuse Cyanobacteria with simple algae. They are prokaryotic autotrophs, not eukaryotes. If you miss this distinction, you lose four marks on a basic classification question.
The idea
Cyanobacteria, such as Anabaena, Nostoc, and Oscillatoria, are photosynthetic autotrophs. They possess specialized cells called heterocysts for atmospheric nitrogen fixation. By converting nitrogen into organic compounds, they enrich soil fertility. They act as primary biofertilisers in paddy fields, significantly increasing crop yield.
Why it matters
They exist to convert atmospheric nitrogen into forms usable by plants, supporting plant growth in nitrogen-deficient environments like aquatic or waterlogged soils.
NEET lens
NEET focuses on the role of heterocysts and their specific association with paddy fields. Remember: they are biofertilisers, not pathogens. Always link Anabaena and Nostoc to nitrogen fixation to secure the mark.
Clinical significance
Cyanobacteria are critical to global nitrogen cycling. Without them, nitrogen fixation rates in aquatic and terrestrial ecosystems would plummet, leading to a collapse in primary productivity. This would trigger a catastrophic failure in the global food chain, directly impacting human nutritional security.
Introduction
Cyanobacteria are photosynthetic autotrophic microbes widely distributed in aquatic and terrestrial environments; many of them fix atmospheric nitrogen.
Core concept
Examples: Anabaena, Nostoc, Oscillatoria. In paddy fields, cyanobacteria serve as an important biofertiliser. Blue-green algae also add organic matter to the soil and increase its fertility. Many cyanobacteria have specialised cells called heterocysts that fix nitrogen. Some cyanobacteria (e.g. Anabaena) can also form symbiotic associations — e.g. with the water fern Azolla, which is used in rice fields.
Go deeper
Cyanobacteria were among the earliest photosynthetic organisms and helped build up oxygen in Earth's atmosphere.
From Class 10
Blue-green 'algae' growing in rice fields add nitrogen to the soil naturally.