#147 Classification

Classification is arranging different kinds of organisms into groups.













Taxonomy
Taxonomy is the study and practice of classification, which involves placing organisms in a series of taxonomic units, or taxa.

	Bacteria	Archaea		Eukarya
	prokaryotic			eukaryotic
nucleus	absent			present
membrane-bound organelles	absent			present
DNA	- circular “chromosome” - no histone proteins associated - smaller circular DNA molecules: plasmid			- inside the nucleus - arranged as linear chromosomes - has histone proteins - mitochondria and chloroplasts have circular DNA
ribosomes	70S < eukaryotes	70S < eukaryotes similar features		80S in cytosol > prokaryotes
cell wall	present, peptidoglycan	present, no peptidoglycan		some do, some don’t
cell division	binary fission			mitosis
reproduction				sexually/asexually
unique			extremophiles – inhabit extreme environments	great diversity of forms - unicellular - colonial - multicellular organisms

1. Kingdom Protoctista (eukaryotic)

• mostly single-celled or groups of similar cells
• some are protozoa: have animal-like cells (no cell walls) 
• some are algae: have plant-like cells (cellulose cell wall and chloroplasts)

2. Kingdom Fungi (eukaryotic)

• no chlorophyll --> does not photosynthesise
• heterotrophic nutrition: use organic compounds (carbon) made by other organisms as its source of energy and molecules for metabolism from                                                                                                 - dead and deccaying matter                                                                                                             - feeding as parasites on living organisms
• reproduce by spores
• simple body form: unicellular or made of long threads called hyphae (with or w/o cross walls)
• cell walls of chitin (not cellulose)
• no cilia or flagella

Kingdom	Plantae	Animalia
	- multicellular eukaryotes - cells differentiated to form tissues and organs
specialised cells	few types	many types
chloroplasts	ü photosynthetic organism	û
vacuole	- large, permanent - for support	- small, temporary
nutrition	autotrophic	heterotrophic
	cells sometimes contain flagella	cells sometimes contain cilia and flagella
unique	- complex bodies - highly branhed above and below ground	- communication by nervous system

Virus

• microorganisms, only visible under an electron microsope
• acellular (cellular structure unlike bacteria and fungi)
• show none of the features traditionally used for classification

Some features:

• have particles made of protein and nucleic acid
• in free environment, viruses are infectious, but have no metabolism
• when viruses infect cells --> use biochemical machinery of host cell to copy their nucleic acid and make proteins to destroy the host cell
• energy provided by respiration in host cell

Taxonomy system - classified by:

• which disease the virus causes
• type of nucleic acid (RNA or DNA)
• whether nucleic acid is single or double stranded

Syllabus 2016-2018 18.2 Classification Organisms studied locally may be used to show how hierarchical classification systems are organised. a) describe the classification of species into the taxonomic hierarchy of domain, kingdom, phylum, class, order, family, genus and species  b) outline the characteristic features of the three domains Archaea, Bacteria and Eukarya  c) outline the characteristic features of the kingdoms Protoctista, Fungi, Plantae and Animalia  d) explain why viruses are not included in the three domain classification and outline how they are classified, limited to type of nucleic acid (RNA or DNA) and whether these are single stranded or double stranded