What is Nostoc Structure and its Colony? Reproduction and Life Cycle Explained
Nostoc is a genus of blue-green algae belonging to cyanobacteria. It is a prokaryotic, photosynthetic organism that commonly occurs as gelatinous colonies in freshwater habitats. Nostoc performs photosynthesis and is also capable of nitrogen fixation, making it ecologically important. It is often found as free-living colonies in ponds and lakes, attached to rocks or tree trunks, and sometimes in symbiotic association with plants and lichens.
The organism forms visible jelly-like masses composed of numerous filaments embedded in mucilage. Because of its colonial structure, nitrogen-fixing ability, and simple prokaryotic organization, Nostoc is frequently studied in biological classification and algal morphology for NEET.
Important Features:
Prokaryotic organism
Photosynthetic cyanobacterium
Nitrogen-fixing ability
Colonial filamentous body
Found in freshwater and moist environments
Systematic Position of Nostoc
The systematic position of Nostoc is given below:
Nostoc is grouped with bacteria because it lacks a true nucleus and membrane-bound organelles. However, due to photosynthesis, it is traditionally studied under algae.
Nostoc Habitat and Distribution
Nostoc is widely distributed in nature. It is commonly found in:
freshwater ponds and lakes
moist soil surfaces
rice fields
wet rocks
tree trunks
symbiotic associations with plants
lichens and bryophytes
Some species live as endosymbionts with fungi or plants. Nostoc can also survive extreme environmental conditions due to protective mucilage.
Morphology of Nostoc
The morphology of Nostoc shows a colonial organization with multiple filaments embedded in a gelatinous mass. The colony may appear spherical, irregular, or flattened.
Nostoc Colony Features
gelatinous and jelly-like
visible to naked eye
greenish or bluish-green colour
colonies may grow large
composed of many filaments
Each filament is called a trichome, which consists of a chain of cells arranged like beads.
Structure of Nostoc
The structure of Nostoc consists of several filaments embedded in mucilage. Each filament is unbranched and composed of a series of cells.
Important structural components:
1. Trichome
A trichome is a chain of cells arranged in a linear manner. Many trichomes together form the colony.
2. Vegetative Cells
These cells perform photosynthesis and form the main body of the filament. They are:
spherical or oval
photosynthetic
thick-walled
arranged in chains
3. Heterocysts
Heterocysts are specialized cells present in Nostoc filaments. These cells are:
larger than vegetative cells
thick-walled
pale coloured
nitrogen-fixing
Nitrogen fixation occurs in heterocysts through the enzyme nitrogenase.
4. Akinetes
Akinetes are thick-walled resting spores. These cells help Nostoc survive unfavourable conditions.
Vegetative Structure of Nostoc
The vegetative structure of Nostoc includes:
gelatinous sheath
trichomes
vegetative cells
heterocysts
akinetes
The mucilaginous sheath protects the colony and retains moisture. The sheath is made of polysaccharides and proteins.
The cells contain pigments such as:
chlorophyll a
phycocyanin
phycoerythrin
These pigments help in photosynthesis.
Nostoc Characteristics
Important Nostoc characteristics include:
prokaryotic cyanobacterium
filamentous colony
mucilaginous sheath
photosynthetic pigments
heterocysts present
nitrogen fixation
reproduction by fragmentation
asexual reproduction by akinetes
symbiotic associations
These features distinguish Nostoc from other algae.
Nostoc Reproduction
Nostoc Reproduction occurs by vegetative and asexual methods. Sexual reproduction is absent.
1. Vegetative Reproduction
Vegetative reproduction occurs mainly by fragmentation. When a filament breaks into smaller pieces, each fragment develops into a new colony.
2. Hormogonia Formation
Hormogonia are small filament fragments formed by breakage of trichomes. These fragments detach and grow into new colonies.
2. Asexual Reproduction
Asexual reproduction occurs by akinetes. These are thick-walled resting spores formed under unfavourable conditions.
Steps:
vegetative cell enlarges
thick wall forms
food reserves accumulate
cell becomes dormant
germination forms new filament
Akinetes help survival during harsh conditions.
3. Reproduction by Heterocysts
Heterocysts may also separate from the filament and form new filaments. This is another method of propagation.
Life Cycle of Nostoc
The life cycle of Nostoc is simple and does not involve sexual reproduction. The main stages include:
Vegetative colony formation
Fragmentation into hormogonia
Growth into new colonies
Akinete formation under stress
Germination of akinetes
Development of new filaments
This cycle allows Nostoc to survive in diverse environments.
Nostoc and Anabaena are Examples of
cyanobacteria
nitrogen-fixing algae
prokaryotic photosynthetic organisms
heterocyst-bearing filamentous forms
Both organisms play important roles in soil fertility.
Ecological Importance of Nostoc
Nostoc plays an important role in ecosystems.
1. Nitrogen fixation
Nostoc converts atmospheric nitrogen into usable forms such as ammonia and nitrates. This improves soil fertility.
2. Soil Enrichment
Used in rice fields to increase nutrient value.
3. Symbiotic Association
Nostoc forms symbiotic relationships with:
Anthoceros
Azolla
lichens
bryophytes
4. Food Source
Some species are edible and used as food in certain countries.
5. Environmental Applications
Nostoc may be used in:
bioremediation
biofuel production
pollution control
antibiotic production
6. Nostoc Species Examples
Common Nostoc species include:
Nostoc commune
Nostoc punctiforme
Nostoc azollae
Nostoc pruniforme
Nostoc flagelliforme
Some species are edible and some form symbiotic associations.
Difference Between Nostoc and Other Algae
Key Takeaways from Experts
Nostoc is a filamentous cyanobacterium forming gelatinous colonies. It contains heterocysts for nitrogen fixation and reproduces mainly by fragmentation and akinetes. Nostoc is ecologically important for soil fertility and symbiotic associations. It is a prokaryotic photosynthetic organism classified under cyanobacteria.
Also Check
FAQs on Nostoc: Structure, Classification, Life Cycle, Diagram and Reproduction
1. What is Nostoc in biology?
Nostoc is a genus of photosynthetic cyanobacteria that forms jelly-like colonies in moist environments. It is a prokaryotic organism with filamentous cells embedded in a mucilaginous sheath. The structure of Nostoc includes vegetative cells and heterocysts, and colonies often appear as green gelatinous masses.
2. Is Nostoc algae harmful?
Most species of Nostoc algae are not harmful to plants or animals and play a beneficial role in nitrogen fixation. However, some aquatic Nostoc species can produce toxic compounds under certain environmental conditions.
3. Why is Nostoc called cyanobacteria?
Nostoc is called cyanobacteria because it contains blue-green photosynthetic pigments and has a prokaryotic cell structure. According to Nostoc classification, it belongs to cyanobacteria and performs photosynthesis similar to algae.
4. What is another name for Nostoc?
Nostoc is commonly known as star jelly, witch’s butter, mare’s eggs, and facai. These names come from the gelatinous Nostoc colony appearance seen in moist habitats.
5. Why is Nostoc called star jelly?
Nostoc is called star jelly because its gelatinous colonies appear suddenly after rain, forming translucent masses that look like jelly. This unusual morphology of Nostoc led to the belief that it fell from stars.
6. Does Nostoc produce oxygen?
Yes, Nostoc performs oxygenic photosynthesis. During photosynthesis, it releases oxygen while producing food. This is an important characteristic of Nostoc and helps maintain ecological balance.
7. How long can Nostoc survive without water?
Nostoc can survive long periods of dehydration by forming dormant structures. Some species can remain inactive for decades and revive when water becomes available, which is part of the life cycle of Nostoc.
8. How to grow Nostoc?
Nostoc grows in moist environments such as ponds, wet soil, and rice fields. It develops naturally when water is available, and colonies expand through Nostoc reproduction by fragmentation and hormogonia formation.
