2.Biological Classification

●Aristotle was the earliest to attempt a more scientific basis for classification.

●He used simple morphological characters to classify plants into trees, shrubs and herbs.

●He also divided animals into two groups, those which had red blood and those that did not.

►Two Kingdom system of classification with Plantae and Animalia kingdoms was developed by Linnaeus.

Drawbacks:

 ● Did not distinguish between

•        the eukaryotes and prokaryotes,
•         unicellular and multicellular organisms
•        photosynthetic (green algae)and non-photosynthetic (fungi) organisms.

►Five Kingdom Classification was given by R.H. Whittaker (1969)

•     Monera
•       Protista
•      Fungi,
•      Plantae
•        Animalia

●The main criteria for classification used by R.H. Whittaker include

•     cell structure
•     thallus(body) organisation
•     mode of nutrition
•     reproduction (mode of reproduction)
•     phylogenetic(evolutionary) relationships.

●When such characterstics were considered, the fungi were placed in a separate kingdom – Kingdom Fungi.

●All prokaryotic organisms were grouped together under Kingdom Monera

●The unicellular eukaryotic organisms were placed in Kingdom Protista.

●Kingdom Protista has brought together Chlamydomonas, Chlorella (earlier placed in Algae within Plants and both having cell walls) with Paramoecium and Amoeba (which were earlier placed in the animal kingdom) which lack it.

►Kingdom Monera

●Bacteria are the sole members of the Kingdom Monera.

●Most abundant micro-organisms, found almost everywhere.

● They also live in extreme habitats such as hot springs, deserts, snow and deep oceans where very few other life forms can survive. Many of them are parasites.

●Bacteria are grouped under four categories based on their shape:

•    the spherical Coccus (pl.: cocci),
•    the rod-shaped Bacillus (pl.: bacilli),
•    the comma-shaped Vibrium (pl.: vibrio)
•    the spiral Spirillum (pl.: spirilla)

●The bacterial structure is very simple, they are very complex in behavior.
  (bacteria show the most extensive metabolic diversity)

• Some of the bacteria are autotrophic, i.e., they synthesise their own food from inorganic substrates.
• They may be photosynthetic autotrophic or chemosynthetic autotrophic.
• The vast majority of bacteria are heterotrophs, i.e., they do not synthesise their own food but depend on other organisms or on dead organic matter for food.