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| Question | Answer |
| Early classification systems only used observable features to place organisms into groups. Why is this not used now? | Scientists do not always agree on the relative importance of different features and groups based solely on physical features may not show how related organisms are |
| Classification systems are now based on observable features along with.... | Embryological evidence Fossil evidence Molecular evidence |
| What does gathering molecular evidence involve? | Analysing the similarities in proteins and DNA. You can compare things like: How DNA is stored and the sequence of DNA bases The sequence of amino acids in proteins from different organisms |
| Complete the sentences: New technologies (e.g. new DNA _______ techniques, better _________) can result in new ______________ being made. How organisms are classified is continually ________ to take account of any new findings that scientists discover. | New technologies (e.g. new DNA ANALYSIS techniques, better BETTER MICROSCOPES) can result in new DISCOVERIES being made. How organisms are classified is continually REVISED to take account of any new findings that scientists discover. |
| What has now replaced the five kingdom classification system? | The three domain system (proposed in 1990) |
| What is the three domain classification system? |
Organisms that were in the kingdom Prokaryotae (which contains unicellular organisms without a nucleus) are separated into two domains - the Archae and Bacteria.
Organisms with cells that contain a nucleus are placed in the domain Eukarya.
They lower hierarchy stays the same - Kingdom, Phylum, Class, Order, Family, Genus and Species.
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| Why were the Prokaryotae reclassified into two domains? | New evidence showed large differences between the Archaea and Bacteria |
| What was the new evidence that supported the three domain system? | MOLECULAR The enzyme RNA polymerase is different in Bacteria and Archaea Archaea, but not Bacteria, have similar histones (proteins that bind to DNA) to Eukarya CELLULAR The bonds of the lipids in the cell membranes of Bacteria and Archaea are different The development and composition of flagellae are also different |
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