Biology BIOLOGICAL CLASSIFICATION

Kingdom-Monera (Blue-Green Algae)

(A) According to Two kingdom system B.G.A. were included in class Cyanophyceae or Myxophyceae of Algae.
But now they are included in Kingdom Monera, because of their prokaryotic nature.
(B) B.G.A. is now known as Cyanobacteria. The name cyanobacteria was suggested by ICNB [lnternationa Code of Nomenclature for Bacteria] in 1978.
(C) BGA are found in freshwater (mostly), marine water and terrestrial habitat.
# Cyanobacteria are photosynthetic oxygenic prokaryotes.
(D) Cyanobacteria were the first organism that produce oxygen on earth.
They have following pigments -
� Chlrophyll 'a' - green
� Carotenoids - yellow
� C- Phycocyanin - blue
� C- Phycoerythrin - red
NOTE : Cyanobacteria are not always of blue-green colour. eg. Trichodesmium is red coloured.
The red colour of water of red sea is due to this alga.

Different forms of BGA or Cyanobacteria :

(A) Unicellular:- Some B.G.A. are unicellular.
eg- Spirulina
NOTE - Spirulina is an edible BGA because it has very large amount of protiens. It can be grown artificially in water tanks. It is used as a fodder for cattle.

Structure of B.G.A.

A. The strucure of BGA is similar to Gram (-ve) eubacteria.
B. BGA is surrounded by mucilagenous sheath. This sheath is made up of mucopolysaccharides (Pectic acid).
The cell wall of BGA is also bilayered. Outer wall is made up of lipopolysaccharides and the inner wall is made up of peptidoglycan.
C. The cell membrane of BGA is also made up of lipoprotiens like that of eubacteria.

The cytoplasm of BGA is divided into two parts :
(a) Peripheral Cytoplasm- It is known as chromoplasm. In this part gas vacoules and photosynthetic thylakoids are found. Photosynthetic pigments are present on the surface of these thyllakoids.