Biology NCERT CBSE ICSE NEET

Definition of biology with description

Cyanobacteria

These are also called as Blue-Green algae (Cyanin - blue-green)

They are prokaryotic,  photosynthetic, autotrophic to bacteria.

They are present in lakes, ponds, rivers, tanks, etc.

Anabaena lives as a symbiont with Azolla in paddy fields and fixes nitrogen. It acts as a biofertilizer. 

They grow well when nitrogen to phosphorus ratio will be low.

These are photosynthetic bacteria that release oxygen in photosynthesis because of the presence of Chlorophyll a  pigment. They are the most primitive organisms showing oxygenic photosynthesis.

The principal pigments are chlorophylls a (green), c-phycocyanin (blue) and c-phyco- erythrin (red).

These are aquatic or terrestrial. Cyanobacteria are present in a wide range of habitats viz. marine, freshwater, soil, biological soil crusts, snow, cryoconites, etc.

These are unicellular (Chroococcum), colonial (Microcystis) or filamentous (Spirulina, Nostoc, Anabaena).

Filament, trichome, colony or cell is covered by a mucilaginous sheath, so they are called as Myxophycea.

Protoplasm is divided into central colourless centroplasm with chromatin material and peripheral pigmented chromoplasm.

Filaments have specialized colorless cells meant for nitrogen fixation called Hetercysts (Nostoc, Anabaena).

They asexually reproduce by Hormogonia or thick walled Akinetes. Flagella are absent in life cycle. They do not reproduce sexually. 

The red color of redsea is due to a phycobilin known as Phycoerythrin in the BGA known as Trichodesmium erythrium.

The accumulation of these algae is termed as ‘algal blooms’. These blooms discolour the water and produce unpleasant taste and odour. They affect the fish population and reduces water quality. The decomposition of these blooms deplete the oxygen (BOD) and triggers the killing of fish.

Eubacteria

1. True bacteria are also called as Eubacteria.

2) Eubacteria were discovered by Anyone Von Leeuenhoek

3) Eubacteria are the most abundant bacteria or Monerans.

4) Eubacteria are ubiquitous I.e., they are present everywhere. 

5) The mode of nutrition may be autotrophic, symbiotic, parasitic or saprophytic. 

Photoautotrophic - Chlorobium

Photoheterotrophic - Rhodospirillum Chemoautotrophic - Nitrifying bacteria

Chemoheterotrophs - symbionts, parasites and saprophytes. 

Parasitic on other bacteria - Bdellovibriobacteriovorous 

6) They may show aerobic or anaerobic respiration. 

7) They are of different sizes and shapes like Coccus, Bacillus, Vibrio, Spirillum, Mycelial. But some show pleomorphy that is they exist in different forms. 

8) Glyocalyx is a polysaccharide covering around the cell wall.

9) Loosely arranged Glyocalyx is called  slime layer.

10) Compactly arranged Glyocalyx is called  Capsule. 

11) Cell wall has non-cellulosic. It is made up of peptidoglycan or mureins. 12) Gram +ve bacteria have Teichoic acid also in the cell wall. 

13) Cell membrane has globular or finger like infoldings called vesicles, tubules or lamellae called mesosomes.

14) Mesospmes are helpful in DNA replication, septum formation during cell division and respiration.

15) The locomotary organelle in bacteria are Flagella.

16) Cells may be Trichous or Atrichous on the basis of presence or absence of flagella. Trichous bacteria may be monotrichus, amphitrichous, lopotrichus or peritrichous.

17) Flagellum doesn't know 9 + 2 arrangement of microtubules. 

18) Flagella are made up of a protein called Flagellin.

19) Eubacteria do not have a true Nucleus. The nucleoid or Incipient nucleus is not surrounded by nuclear membrane. 

20) The genetic material is a double stranded circular DNA (ds cDNA).

21) DNA of Eubacteria is not associated with histone proteins.  

22) Circular extra-chromosomal DNA is known as plasmid or episome.

23) Plasmids are have genes for fertility, antibiotic resistance, toxins and pathogenesis.

24) Eubacteria do not have membrane bound organelles.

25)  Phtosynthetic bacteria have bacterial chlorophyll.

 26) Cytoplasm has free 70S ribosomes or polysomes. 

27) In favourabel conditions, bacteria reproduce asexually by binary fission once in 18-20 minutes. 

28) During unfavorable conditions bacteria reproduces by endospore formation. 

29) The primitive sexual processes like conjugation, transformation and transduction may occur for genetic recombination.

30) Chemosynthetic bacteria play a role in recycling of minrrals.

Archaebacteria

1) Archaebacteria are Monerans and extremophiles which can tolerate extreme conditions

2) Acidophiles live in high acidic conditions (E.g.Sulpholobus)

3) Hyperthermophiles live in high temperature (Eg. Methanopyruskandleri)

4) Halophiles live in high salt concentrations (Eg. Halobacterium) 

5) Methanobacteris or Methanogens live in oxygen lacking or anaerobic  conditions (Eg. Methanobacterium). 

6) Methanogens are present in oxygen lacking conditions like marshes and rumen of cattle to release methane from organic matter. 

7) Archaebacteria have Surface layer known as S-layer with glycoproteins or proteins. It is a monolayer with hexagonal proteins or glycoproteins to resist the host attack from low pH and lytic enzymes.

8) Cell wall lacks mureins, Mucopeptides or Muramic acid, but Pseudomureins are present in the cell wall having Laminoacids as tetrapeptides, N-acetyl glucosamine and N-acetyl TalosamineUronic acid in β1,3 linkage. So lysozyme cannot attack this cell wall. 

9) NAT is associated with L-amino acids such as Glutamic acid, Alanine, Lysine and Glutamic acid.

10) Thermoplasma is without cell wall

11) Cell membrane has L-Glycerol in phospholipids. The fatty acid chain  is linked to the Glycerol by ETHER bonding and the fatty acid chain has branched isoprene units having 5C. This provides very high resistance to archaens. 

12) The lipids are tetraether lipids in thermoplasma which can tolerate high temperatures

13) The genome is circular with double stranded DNA associated with histone proteins.

14) Ribosomes are of 70S type which are sensitive to Diphtheria toxin which inactivates eEF2 on ribosome and inhibits protein synthesis (similarity with eukaryotes).

15) The first amino acid involved in protein synthesis is Methionine like that of Eukryotes.

16) tRNA lacks thymine like that of Eukaryotes.

17) They do not have pathogenic nature. 

18) Chlorophyll based photosynthesis is absent but Chemosynthetic metabolism exists.

A brief account of the Kingdom Monera of Prokaryotes

A very brief account of Classification basics

A brief explanation on early attempts made to classify living organisms