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42 Cards in this Set

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Protobionts
Aggregates of abiotically profuced molecules surrounded by a membrane or membrane-lke structure. Isolated unites separate from its enviornment (pre-life).
Ribozymes
RNA which plays a central role in protein synthesis, can also carry out a number of enzyme-like catalytic functions. Can make complementart copies of short pieces of RNA, provided that they are supplied with nucleotide building blocks.
Radiometric dating
Based on the decay of radioactive fossils. A radioactive "parent" isotope decays to a "daughter" isotope at a constant rate. The rate of decay is expressed by the half-life, the time required for 50% of the remaining parent isotope to decay.
Half-life
The number of years it takes for 50% of the original sample to decay, is unaffected by temperature, pressure, and other enviornmental variables.
Magnetic reversals
Earth's north and south magnetic poles have reversed repeatedly in the past. Affect the entire planet and leave their record on rocks throughout the world.
Stromatolites
The oldest known fossils, dating from 3.5 billion years ago, which are rocklike structures composed of many layers of bacteria and sediment.
Genetic annealing
Produces the genome of eukaryotic cells, in which horizontal gene transfers occured between many different bacterial and archaean lineages.
Snowball Earth hypothesis
Most life would have been confined to areas near deep-sea vents and hot springs or to those sparse regions of the ocean where enough ice had melted for sunlight to penetrate the surface waters.
Colonies
Collections of autonomously replicating cell. Some cells in the colonies became specialized for different functions.
Pangea
About 250 million years ago, near the end of the Paleozoic era, plate movements brought all the previously separated landmasses together into a supercontinent.
Three domain system
Bacteria, Archaea, and Eukarya are essentially superkingdoms, a taxonomic level higher than the kingdom level.
Peptidoglycan
Most bacterial walls contain a network or modified-sugar polymers cross-linked by short polypeptides.
Gram stain
Scientists can classify many bacterial species into two groups based on differences in cell wall composition.
Gram-positive
Bacteria have simpler walls with a relatively large amount of peptidoglycan.
Gram-negative
Bacteria have less peptidoglycan and are structurally more complex, with an outer membrane that contains lipopolysaccharides (carbohydrates bonded to lipids)
Capsule
Covers the cell wall of many prokaryotes and is a sticky layer of polysaccharide or protein.
Fimbriae and pili
Some prokaryotes stick to their substrate or to one another by means of hairlike appendages. Fimbriae are usually more numerous and shorter then pili.
Taxis
Movement toward or away from a stimulus.
Nucleoid region
The prokaryotic chromosome is located in a part of the cytoplasm that appears lighter then the surrounding cytoplasm in electron micrographs.
Plasmids
A typical prokaryotic cell may also have much smaller rings of DNA.
Endospores
Certain bacteria, for example, can form resistant cells when an essential nutrient is lacking in the enviornment.
Photoautotrophs
The photosynthetic organisms that capture light energy and use it to drive the synthesis of organic compounds from CO2. Cyanobacteria and many other groups of prokaryotes are photoautotrophs as are plants and algae.
Chemoautotrophs
Need only CO2 as a carbon source. However, instead of using light for energy, they oxidize inorganic substances, such as hydrogen sulfide, ammonia, or ferrous ions. This mode of nutrition is unique to certain prokaryotes.
Photohetrotrophs
Use light for energy but must obtain their carbon in organic form. A number of marine prokaryotes use this mode of nutrition.
Chemoheterotrophs
Must consume organic molecules for both energy and carbon. This nutritional mode is found widely amond prokaryotes as well as protists, fungi, animals, and even some parasitic plants.
Obligate aerobes
Use O2 for cellular respiration and cannot grow without it.
Facultative anaerobes
Use O2 if it is present but can also grow by fermentation in an anaerobic enviornment.
Obligate anaerobers
Are poisoned by O2. Some lives exclusively by fermentation, other extract chemical energy by anaerobic respiration, in which substances other than O2 accept electrons at the downhill end of electron transport chain.
Nitrogen fixation
Certain prokaryotes, including some cyanobacteria, convert atmospheric nitrogen to ammonia.
Biofilms
In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies.
Extremophiles
Lovers of extreme conditions
Extreme thermophiles
Thrive in very hot enviornments.
Extreme haolphiles
Live in highly saline environments.
Methanogens
Named for the unique way they obtain energy: they use CO2 to oxidize H2 releasing methane as a waste product. Posioned by O2.
Decomposers
Break down corpses, dead vegetation, and waste products thereby unlocking supplies of carbon, nitrogen, and other elements.
Symbiosis
An ecological relationship between organisms of different species that are in direct contact.
Mutualism
Both symbiotic organisms benefit
Commensalism
One organism benefits while neither hamring nor helping the other in any significant way.
Parasitism
One organism, called a parasite, benefits at the expense of the host.
Exotoxins
Proteins secreted by prokaryotes.
Endotoxins
Are lipopolysaccharide components of the outer membrance of gram-negative bacteria. Are released only when the bacteria die and their cell walls break down.
Bioremediation
Prokayotes are the principal agents in the use of organisms to remove pollutants from soil air or water.