Biological Classification
Classification
The process of grouping living organisms into convenient categories based on simple
characters is known as classification.
1. Two kingdom classification
Carolus Linnaeus divided all living things into two kingdoms- Plantae and Animalia.
2. Five kingdom classification
R.H. Whittaker divided all living things into five kingdoms- Monera, Protista, Fungi, Plantae,
and Animalia.
The main criteria for classification included
o cell structure
o thallus organisation
o mode of nutrition
o reproduction
o phylogenetic relationship (evolutionary relationship)
Kingdom Monera
It includes all prokaryotes. Bacteria are the sole members of this kingdom.
They have autotrophic (photosynthetic or chemosynthetic) or heterotrophic mode of
nutrition.
Bacteria can be classified into four categories based on their shapes.
o Spirillum – spiral-shaped
o Coccus – spherical-shaped
o Bacillus – rod-shaped
o Vibrium – comma-shaped
1. Archaebacteria
It includes halophiles, which are found in extreme salty areas; thermoacidophiles, which
are found in hot springs; and methanogens, which are found in marshy areas.
Methanogens are found in the gut of ruminants and are used for the production of biogas
from cow dung.
2. Eubacteria (also known as true bacteria)
It includes blue-green algae (cyanobacteria) such as Nostoc, Anabaena, etc.
Photosynthetic bacteria contain chlorophyll a. Chemosynthetic bacteria oxidise various
inorganic compounds and use the released energy for their ATP production.
They have rigid cell wall and flagellum (if motile) for locomotion.
They have specialised cells known as heterocysts, which are involved in nitrogen fixation.
Bacteria reproduce mainly by binary fission. Spore formation and primitive type of DNA
transfer techniques from one bacterium to another are also seen for reproduction.
Mycoplasma is the smallest cell that can survive in the absence of oxygen and completely
lacks a cell wall. Many of them are pathogenic to plants and animals.
Viruses
