Affinities of Cyanophyceae:
The members of Cyanophyceae show some relationship with both bacteria and Rhodophyceae.
Similarities of Cyanophyceae with Bacteria:
1. Cell structure is prokaryotic in both the group, having unorganised nucleus and devoid of membrane bound organelle.
2. The capsule of bacteria (if present) and mucilaginous sheath of blue green algal cells are made up of fine fibrils.
3. Cell wall composed of mucopeptide (murein).
4. Oscillatoria (blue green alga) shows similarity with Beggiatoa (sulphur bacterium), both in shape and movement.
5. Both are sensitive to antibiotics.
6. Both the groups show similarity in many metabolic processes like nitrogen and sulphur metabolism.
7. Absence of sexual reproduction.
8. Genetic recombination has been reported in Anacystis nidulans, a member of Cyanophyceae, showing similarity with bacteria.
ADVERTISEMENTS:
Similarities of Cyanophyceae with Rhodophyceae (Red Algae):
1. Both the groups resemble in the absence of motile cells.
2. The Cyanophycean pigments, c-phycocyanin (blue) and c-phycoerythrin (red) are chemically similar to the Rhodophycean pigment r-phycocyanin and r-phycoerythrin.
3. Stignema and some other members of Cyanophyceae have pit connections, and show relationship by having similar structures as found in the members of Rhodophyceae.
Economic Importance of Cyanophyceae:
The Cyanophycean members show both beneficial and harmful activities.
Beneficial Activities:
1. Nostoc commune is boiled and used as soup in China.
2. Few species of Nostoc, Anabaena, Scytonema form a thick substratum over the soil resulting a reclamation of land.
3. About twenty two (22) filamentous members of Cyanophyceae like Nostoc, Anabaena, Aulosira, Anabinopsis, Calothrix, Scytonema etc. can fix atmospheric nitrogen and form nitrogenous compounds. These compounds are further absorbed by the plant for their metabolic activity and increase yield.
All the above members have heterocyst. But certain non-heterocystous members like Plectonema boryanum are able to fix atmospheric nitrogen in anaerobic condition.
Harmful Activities:
1. Some members of Cyanophyceae cause damage of building plasters, stones etc. It can be avoided by spraying CuSO4 and sodium arcenate.
2. Some members like Microcystis, Anabaena, form water blooms and can grow well in O2 deficient water. Continuous respiration by submerged plants and animals during night time (when photosynthesis does not take place) causes the depletion of O2 to almost zero level. At that condition mortality of both animals and other submerged plants takes place due to suffocation.
3. Blue green algae contaminate the water of reservoirs. They develop a foul odour in water and make it unhygienic for human being and cause several diseases.
Different diseases like gastric troubles may appear by drinking the water contaminated with Microcystis and Anabaena.
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