This document contains summarised notes for Topic 3 Classification, taken using the Pearson Edexcel B biology activate textbook. Notes taken with referencing to specification.
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
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
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