Topic 3 summary notes (A Level Biology Edexcel B)

CLASSIFICATION

PRINCIPLES/SPECIES
3 DOMAINS
 Archaea
 Eukaryota More closely related to each other
 Bacteria
Archaea are more closely related to the ancestral form than eukaryote
Most distantly related: eukaryote and bacteria

ARCHAEA: ARCHAEBACTERIA (ancient bacteria)
BACTERIA: EUBACTERIA (true bacteria)
EUKARYOTA: PROTOCISTA (microscopic organisms, heterotrophs, autotrophs)
FUNGI (heterotrophs) (have chitin not cellulose)
PLANTAE (autotrophs)
ANIMALIA (heterotrophs)

LARGEST TO SMALLEST
Domain, Kingdom, Phylum, Class, Order, Family, Genus and Species

FIRST NAME: genus
SECOND NAME: species

SPECIES – a group of organisms with similar characteristics that interbreed to produce fertile
offspring
SEXUAL DIMORPHISM – huge difference between the appearance of the male and female of
a species, different sexes could well be thought to be different species in a morphological
species model.
LIMITATIONS OF SEXUAL DIMORPHISM
 All of the organisms cannot attempt to interbreed to produce fertile offspring as they
don’t all live in the same area
 2 individuals from different populations mate, they’re considered the same species if
fertile offspring’s produced

CONCEPT OF SPECIES
 Species n.o used to measure biodiversity
 Look for changes in species to monitor effect of natural environmental changes and
changes from human activity
MORPHOLOGICAL SPECIES CONCEPT – based on appearance of the organisms
 Before this was used widely and still is but appearance of an organism can be
affected by many different things
 Huge amounts of variation within a group of closely related organisms

PRINCIPLES OF CLASSIFACTION

WHY CLASSIFY?
 Enormous variety of organisms

,  Great variety of names
 Need a way of identifying the different groups of organisms
 Organisms are put in groups based on their similarities and differences
HISTORY OF TAXONOMY
BEFORE – organisms grouped based on physical appearance or morphology

SPECIES MODELS
ECOLOGICAL SPECIES MODEL – based on ecological niche, not robust
MATE-RECOGNITION SPECIES MODEL – based on unique fertilisation systems, including
mating and cross-pollination
GENETIC SPECIES MODEL – based on DNA evidence, collecting DNA was expensive, now
cheaper/faster
EVOLUTIONARY SPECIES MODEL – based on shared evolutionary relationships, not always
clear pathway

LIMITATIONS OF SPECIES MODEL
 Finding evidence
 Many organisms don’t reproduce sexually
 Fossil organisms cannot reproduce and don’t

IDENTIFYING A SPECIES
 Simple identification apps – simple tool
 Instruments – help identify DNA in the field
 Paper-based catalogue – everyone around the world has access to classification info

DNA SEQUENCING
 Base sequences of genome of organism worked out, leads to DNA PROFILING which
looks at non-coding areas of DNA to identify patterns
 Similarity of patterns can be used to identify relations between species
BIOINFORMATICS – development of a software and computing tools to analyse raw
biological data (quick, makes sense)
DNA BARCODES – organisms in a field may not be identified easily
 So this is currently developing for species identification
 Looks at short genetic sequences from a genome

EVOLUTION

OLD EVIDENCE – relied on similarities in the appearance of living organisms and fossil
evidence.
 Can cause problems when looking at similar species as they’ve evolved in response
to similar niches.
 Developments: DNA profiling

The more mutations in DNA, the longer the time since they had a common ancestor


FOSSIL AND HUMAN EVOLUTION