2. Evolution of Classification Systems Flashcards
(15 cards)
What did classification systems USED to be based on
- Early classification systems ONLY used observable features to place organisms into groups.
- But this method has problems. Scientists dont always agree on the relative importance of different features & groups based solely on physical features may not show how related organisms are. (eg. sharks & whales look similar, but not acc closely related & are even diff classes).
What are classification systems based on
- The more similar organisms are, the more related they are. Now use wide range of evidence to see how similar, therefore how related, organisms are:
- Molecular evidence
- Embryological evidence
- Anatomical evidence
- Behavioural evidence
What are classification systems based on: 1. Molecular evidence
- Similarities in proteins & DNA. More closely related organisms will have more similar molecules.
- Can compare how DNA is stored & sequence of DNA bases (Eg. base sequence for human & chimp DNA is abt 94% the same).
- Can also compare sequence of amino acids in proteins from diff organisms. The more similar the amino acid sequence of a protein in 2 diff species, the more closely related the species are likely to be.
What are classification systems based on: 2. Embryological evidence
The similarities in the early stages of an organisms development
What are classification systems based on: 3. Anatomical evidence
The similarities in structure & function of diff body parts
What are classification systems based on: 4. Behavioural evidence
The similarities in behaviour & social organisation of organisms.
How is new technology contributing to new discoveries in relationships between organisms
- New technologies (eg. new DNA techniques, better microscopes) can result in new discoveries being made & relationships between organisms being clarified.
- Scientists can share their new discoveries in meetings & scientific journals. How organisms are classified is continually revise to take account of any new findings discovered.
What has now replaced the 5 kingdom system
the 3 domain system
What is the 3 domain system
- In the older system, the largest groups were in the 5 kingdoms - all organisms were placed into one of these groups.
- In 1990, the 3 domain system proposed. Has 3 domains - large superkingdoms that are above the kingdoms in the taxonomic hierarchy.
How does 3 domain system work
- In 3 domain system, organisms that were in kingdom Prokaryote (unicellular orgs w/o nucleus) are separated into 2 domains - the Archaea & Bacteria.
- Organisms w cells that contain a nucleus are placed in domain Eukarya (this includes 4 of the 5 kingdoms).
- The lower hierarchy stays the same - Kingdom, Phylum, Class, Order, Family, Genus, Species.
see pg121 for simple diagram explaining 3 domain system
Comparison between 5 kingdom & 3 domain system
What led to the proposal of the 3 domain system
Molecular evidence
How did molecular evidence lead to proposal of 3 domain system
- The Prokaryotae were reclassified into 2 domains bc new evidence showed large differences between the Archaea & Bacteria. This ev included:
- Molecular evidence - enzyme RNA polymerase is diff in Bacteria & Archaea. Archaea, but not bacteria, have similar histones to Eukarya.
- Cell membrane evidence - the bonds of the lipids in cell membranes of Bacteria & Archaea are diff. Development & composition of flagellae are also diff.
- Most scientists now agree Archaea & Bacteria evolved separately & that Archaea are more closely related to Eukarya than Bacteria. The 3 domain system reflects how diff the Archaea & Bacteria are.
What is an eg of scientific knowledge always changing & improving
Development of the 3 domain system from the new evidence.
