🌿 Cyanobacteria – Characteristics, Importance & Role in Nitrogen Fixation

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Introduction:

Cyanobacteria, also known as blue-green algae, are some of the oldest life forms on Earth. These prokaryotic, photosynthetic organisms play a vital role in aquatic ecosystems and agriculture. In NEET and board exams, they are frequently asked under the Biological Classification and Plant Kingdom chapters.

What Are Cyanobacteria?

Cyanobacteria are photosynthetic prokaryotes.

They lack a true nucleus and membrane-bound organelles.

They contain chlorophyll a and phycobiliproteins, enabling oxygenic photosynthesis.

Common examples: Nostoc, Anabaena, Oscillatoria, Spirulina


General Characteristics of Cyanobacteria

Feature Description

Cell Type Prokaryotic
Photosynthesis Type Oxygenic (like plants)
Pigments Chlorophyll-a, phycocyanin, phycoerythrin
Habitat Freshwater, marine, moist soil, rocks
Cell Wall Composition Peptidoglycan
Reserve Food Cyanophycean starch
Reproduction Asexual (binary fission, fragmentation, hormogonia)



Special Structures in Cyanobacteria

Heterocysts: Specialized cells for nitrogen fixation

Akinetes: Thick-walled dormant spores for survival

Gas Vacuoles: Help in buoyancy (especially in Microcystis)


Cyanobacteria and Nitrogen Fixation

Some cyanobacteria like Anabaena and Nostoc can fix atmospheric nitrogen in heterocysts under anaerobic conditions.
They are used as biofertilizers in paddy fields.

🔍 Important Application:

Anabaena lives symbiotically in the water fern Azolla, used in rice fields.

Sustainable and eco-friendly alternative to chemical fertilizers.


Cyanobacteria in Ecosystems

Primary producers in aquatic habitats

Increase oxygen levels through photosynthesis

Improve soil fertility

Indicators of water pollution (algal blooms caused by eutrophication)


Cyanobacteria and NEET

💡 NEET MCQs often ask:

Pigments in cyanobacteria

Nitrogen-fixing examples

Features distinguishing them from eukaryotic algae



Diagram: Cyanobacterium (e.g., Nostoc)

🖼️ Include hand-drawn or digital labeled diagram showing heterocyst, vegetative cell, akinete

Conclusion

Cyanobacteria are simple yet powerful organisms contributing significantly to Earth's ecosystems and agriculture. Understanding their features helps clarify many botany concepts, especially for NEET and board exam preparation.

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