Anabaena vs. Nostoc

What's the Difference?

Anabaena and Nostoc are both types of cyanobacteria that belong to the same family, Nostocaceae. They are commonly found in freshwater environments and play a crucial role in nitrogen fixation. However, there are some notable differences between the two. Anabaena is filamentous and forms long chains of cells, while Nostoc is colonial and forms spherical colonies. Anabaena has specialized cells called heterocysts that are responsible for nitrogen fixation, whereas Nostoc has specialized cells called akinetes that help in survival during unfavorable conditions. Additionally, Anabaena can form harmful algal blooms in water bodies, whereas Nostoc is not known to cause such blooms. Overall, both Anabaena and Nostoc are important organisms in aquatic ecosystems, contributing to nutrient cycling and ecological balance.


Cellular OrganizationProkaryoticProkaryotic
Cell Wall CompositionPeptidoglycanPeptidoglycan
Cell ShapeFilamentousFilamentous
Cellular ReproductionAsexualAsexual
Nitrogen FixationYesYes
Colonial FormUnicellular or filamentousUnicellular or filamentous
Specialized CellsHeterocystsHeterocysts
Photosynthetic PigmentsChlorophyll a, phycocyanin, phycoerythrinChlorophyll a, phycocyanin, phycoerythrin

Further Detail


Anabaena and Nostoc are both genera of cyanobacteria, commonly known as blue-green algae. These organisms are photosynthetic and play a crucial role in the nitrogen cycle. While they share several similarities, they also exhibit distinct characteristics that set them apart. In this article, we will explore the attributes of Anabaena and Nostoc, highlighting their morphology, habitat, reproduction, and ecological significance.


Anabaena and Nostoc share a filamentous structure, consisting of chains of cells. However, they differ in their cell arrangement. Anabaena forms unbranched filaments, with cells that are often larger and more elongated. These cells possess specialized structures called heterocysts, which are responsible for nitrogen fixation. On the other hand, Nostoc filaments are typically branched, forming a network-like structure. The cells in Nostoc filaments are generally smaller and more spherical in shape.


Anabaena and Nostoc can be found in a wide range of habitats, including freshwater, marine, and terrestrial environments. However, they exhibit preferences for different conditions. Anabaena is commonly found in freshwater bodies such as lakes, ponds, and rivers. It can also thrive in symbiotic relationships with certain plants, forming specialized structures called heterocystous cyanobacterial symbioses. Nostoc, on the other hand, is often found in terrestrial habitats, such as soil, rocks, and even tree bark. It can form colonies known as "gelatinous masses" in moist environments.


Both Anabaena and Nostoc reproduce through a process called fragmentation. During fragmentation, the filaments break apart, giving rise to new individuals. However, they also have distinct reproductive strategies. Anabaena can reproduce through akinetes, which are specialized resting cells that can withstand harsh environmental conditions. These akinetes can germinate and give rise to new filaments when conditions become favorable. Nostoc, on the other hand, produces specialized cells called hormogonia. These hormogonia are motile and can disperse to new locations, where they can develop into new colonies.

Ecological Significance

Anabaena and Nostoc play vital roles in the environment, particularly in the nitrogen cycle. Both genera are capable of nitrogen fixation, a process by which atmospheric nitrogen is converted into a form that can be utilized by other organisms. This ability makes them important contributors to the fertility of soils and aquatic ecosystems. Additionally, their photosynthetic activity contributes to oxygen production and carbon dioxide fixation, helping to maintain the balance of gases in the atmosphere. Furthermore, Anabaena and Nostoc serve as a food source for various organisms, including aquatic invertebrates and some species of fish.


In conclusion, Anabaena and Nostoc are two genera of cyanobacteria that share similarities in their filamentous structure and ecological significance. However, they differ in their morphology, habitat preferences, and reproductive strategies. Anabaena forms unbranched filaments with larger cells and specialized heterocysts, while Nostoc forms branched filaments with smaller cells. Anabaena is commonly found in freshwater environments, while Nostoc thrives in terrestrial habitats. Both genera contribute to the nitrogen cycle, but Anabaena produces akinetes for reproduction, while Nostoc disperses hormogonia. Understanding the attributes of Anabaena and Nostoc is crucial for comprehending their ecological roles and potential applications in various fields, including agriculture and environmental remediation.

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