Biology Tests 26-27
Terms
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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.