Chapter 10CLASSIFICATION

• Classification: an orderly grouping of organisms • The study of classifying organisms is called

taxonomy– Provides universal names for organisms– Provides a reference for identifying organisms

• There are tow approaches to classification

Convenience vs. Phylogenetic Classification

• THE CLASSIFICATION SCHEMES IN PLACE TODAY ARE MAINLY BASED ON THE CONVENIENCE METHOD.

• ANY PHYLOGENY IS ASSUMED AND NOT PROVED SCIENTIFICALLY.

History of Kingdom• WHITTAKER’S FIVE KINGDOM

CLASSIFICATION - A CONVENIENCE METHOD.

• THE HISTORY OF KINGDOM CLASSIFICATION SCHEMES

• THE FIRST CLASSIFICATION SCHEME WAS DEVELOPED BY ARISTOTLE 2000 YEARS AGO.

• PLANTS AND ANIMALS.

History of Kingdom (continue)

• IN THE LATE 1800’S, A THIRD KINGDOM WAS ADDED: PROTISTA

• IN THE 1950’S, A FORTH KINGDOM WAS ADDED: MONERA

• PROCARYOTIC AND EUCARYOTIC CELL STRUCTURE

History of Kingdom

• IN 1969, A FIFTH KINGDOM WAS ADDED: FUNGI

Taxonomy• 1735 Plant and Animal Kingdoms• 1857 Bacteria & fungi put in the Plant Kingdom• 1866 Kingdom Protista proposed for bacteria,

protozoa, algae, & fungi• 1937 "Prokaryote" introduced for cells "without a

nucleus"• 1961 Prokaryote defined as cells in which nucleoplasm

is not surrounded by a nuclear membrane• 1959 Kingdom Fungi• 1968 Kingdom Prokaryotae proposed• 1978 Two types of prokaryotic cells found

The Basis of Five Kingdom

• WHITTAKER’S FIVE KIGNDOM CLASSIFICATION RELATED ALL ORGANISMS ON THE BASIS OF:

1. MODES OF NUTRITION2. POSITION IN THE ECOLOGICAL FOOD

CHAINA. PRODUCERB. CONSUMERC. DECOMPOSER

The Basis of Five Kingdom (continue)

3. CELLULAR ORGANIZATIONA. SINGLE CELLB. MULTICELLULARC. PROCARYOTIC/EUCARYOTIC

4. EVOLUTIONARY TREND• WITHIN THE INDIVIDUAL KINGDOMS,

ORGANISMS ARE FURTHER GROUPED INTO SMALLER GROUPS AS FOLLOWS:

The Basis of Five Kingdom (continue)

• PHYLUM/DIVISION• CLASS• ORDER• FAMILY• GENUS• SPECIES• STRAIN/VARIANT/SUBSPESCIES

THE PHYLOGENETIC APPROACH

• ORGANISMS THAT ARE GENETICALLY RELATED WILL HAVE MORE CHARACTERISTICS IN COMMON THAN ORGANISMS THAT LOOK A LIKE.

• CARL WOESE AND FRIENDS HAVE BEEN WORKING SINCE 1970 TO PUT IN PLACE A PHYLOGENETIC CLASSIFICATION SCHEME.

THE PHYLOGENETIC APPROACH (continue)

• COMPARE HEREDITARY MOLECULES OF ORGANISMS.

• THEY SELECTED RIBOSOMAL RNA BECAUSE:

• ALL CELLS HAVE IT AND PLENTY OF IT.• ITS FUNCTION IS THE SAME IN ALL CELLS.• ITS NITROGEN BASE SEQUENCE IS

MODERATELY CONSERVED FROM GENERATION TO GENERATION.

THE PHYLOGENETIC APPROACH (continue)

• WOESE SEPARATED ORGANISMS IN THE MONERA INTO TWO GROUPS:

- ARCHAEABACTERIA- EUBACTERIA

• ARCHAEABCTERIA TEND TO THRIVE IN EXTREME ENVIRONMENTS, EUBACTERIA DO NOT.

• ALSO, THERE ARE STRUCTURAL DIFFERENCES BETWEEN THESE TWO GROUPS OF BACTERIA.

The Three-Domain System