Unit 2 Essay

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Biology Unit 2 Exam Revision Notes The Five Kingdoms
Prokaryotes E.g. Bacteria
• no nucleus
• loop of naked DNA
• DNA not arranged in linear chromosomes
• no membrane-bound organelles
• smaller ribosome’s than other groups
• carry out respiration on mesosome’s (special membrane systems), not mitochondria

Taxonomic Hierarchy
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species smaller cells than eukaryotes
• parasitic (some cause disease)
Protoctista E.g. Algae
• eukaryotes
• mostly single-celled
• autotrophic/heterotrophic nutrition
• do not belong to any other kingdoms
Fungi E.g. Moulds, yeast, mushrooms
• multi-cellular eukaryotes
• heterotrophic (plants and animals) and saptrophic (absorb food from the dead)
Plantae E.g. Mosses, Ferns, flowering plants
• multi-cellular eukaryotes
• cells surrounded by cellulose cell wall
• produce multi-cellular embryos from fertilised eggs
• autotrophic (make their own food) nutrition
Animalia E.g. molluscs, insects, fish, reptiles, birds, mammals
• multi-cellular eukaryotes
• heterotrophic (plants and animals) nutrition
• fertilised eggs that develop
• usually able to move around
Binomial Naming System: Genus then Species : minimises confusion – all scientists, in all countries, call a species by the same name. Evolution of Classification:
Only use to be based on observations to place organisms into groups, but physical features may not show how closely related organisms are. Now, it’s based on observations and evidence. The more similar, the more closely related, the other evidence used:
• Molecular: similarities in DNA etc. e.g. Chimps and Humans share 94% of DNA.
• Embryological: early stages of development.
• Anatomical: structure/function of body parts.
• Behavioural: similarities in behaviour and social organisation. New Scientific Data can lead to new taxonomic groupings:
 New data about any of characteristics can influence the way species are classified
 New data has to be evaluated by other scientists to check if it’s actually there. If all scientists agree it can lead to a new organism being reclassified or leads to changes in the classification system structure 3 Domains
Bacteria have:
• different cell membrane structure
• different internal structure of the flagella
• different enzymes (RNA polymerase) for building RNA
• no proteins bound to their genetic material
• different mechanisms for DNA replication and building RNA Archaea and Eucarya share:
• similar enzymes (RNA polymerase) for building RNA
• similar mechanisms for DNA replication and building DNA
• production of some proteins that bind to their DNA Bacteria: Prokaryote kingdom e.g. methanogens
Archaea: Prokaryote kingdom e.g. all other bacteria (apart from methanogens)
Eucarya: Organisms from the other four kingdoms (not prokaryote), Eukaryotic e.g. plants/ animals/ fungi Three domains vs Five Kingdoms
A new, three domain classification system has been proposed (1960) based on new data. The new data came from molecular phylogeny (study of the evolutionary history of groups of organisms, telling us which species are related to which and how closely related they are). Molecular phylogeny looks at molecules (DNA and proteins) to see how closely related organisms are, e.g. more closely related organisms have more similar molecules This new system classifies organisms in a different way:
 In the older, five kingdom system of classification, all organisms are placed into one of five kingdoms
 In the new, three domain system all organisms are placed into one of three domains – large super -kingdoms that are above the kingdoms in the taxonomic hierarchy
 Organisms that were in the kingdom Prokaryote (unicellular organisms without a nucleus) are separated into two domains – the Archaea and Bacteria. Organisms from the other four kingdoms (organisms with cells that…