ibsl biology: option d
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Option D
Ecology
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Spontaneous Origin of Life
• Spontaneous generation of life from inorganic matter can not take place; cells can only come from other cells
• To form the first cells:– Chemical reactions to produce organic
molecules– These molecules would have to form
polymers– Polymers would have to be able to self
replicate–Membranes would have to be able to
develop
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Origin of Organic Compounds
• Possible locations for synthesis of organic compounds:–Miller and Urey: atmosphere and water
on the surface of the Earth– Unusual chemical conditions around
hydrothermal vents deep in the oceans– Extraterrestrial origin: formed in space
and brought to earth via meteorites, comets, etc
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Miller and Urey
• Stanley Miller and Harold Urey 1953• Recreated Earth conditions–Mixed gases ammonia, methane, and
hydrogen
• After one week the water was murky brown with many organic compounds (including fifteen amino acids)
• Could have spontaneous formation of organic compounds on Earth
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The Role of RNA in the Origin of Life
• RNA could have been used instead of both DNA and enzymes
• RNA catalyses a broad range of chemical reactions; could have carried out enzyme activity
• RNA can self-replicate; can synthesize and use templates with complementary base pairings
• RNA was superseded by DNA as the genetic material and by proteins as the catalysts of life
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Membranes and Protobionts
• Phospholipids naturally form bilayers that form spherical structures to enclose a droplet of fluid (microspheres)
• Coacervate: water that contains these membrane-bound microspheres
• Protobionts: These phospholipid microspheres with different internal conditions from the external conditions
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The Endosymbiotic Theory
• Endosymbiotic Theory: both mitochondria and chloroplasts have evolved from independent prokaryotic cells, which were taken into a larger heterotrophic cell by endocytosis. They were kept alive and continued to carry out aerobic respiration and photosynthesis
• The characteristics of mitochondria and chloroplasts support this: they grow/divide, naked loop of DNA, synthesize some of their own, double membranes
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Explosion of Life on Earth
• Once eukaryotic chromosomes, meiosis, and sexual reproduction evolved, evolution could take place at a much more rapid pace
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Prokaryotes and the Atmosphere
• Prokaryotes were the first organisms on Earth to use photosynthesis; oxygen released as a waste when water was its source of hydrogen
• Concentrations of oxygen built up• Other prokaryotic organisms could
use aerobic cell respiration once the atmosphere contained oxygen
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Gene Pools and Allele Frequencies
• Gene Pool: All the genes in an interbreeding population
• Allele frequency: the frequency of an allele, as a proportion of all alleles of the gene in the population
• Allele frequency can range from 0.0 to 1.0
• Evolution always involves a change in allele frequency in the gene pool over several generations
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What is a species?
• Morphological definition: type of living organism with fixed characteristics– Species can usually be distinguished by characteristics– Does not recognize the fact that species evolve
• Species: group of actually or potentially interbreeding populations, with a common gene pool, which are reproductively isolated from other such groups (must be able to interbreed)– Conflicts with species definition: sibling species
difficult to identify, some species with clearly different characteristics will interbreed, some are asexual, fossils can’t be classified
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Speciation
• Speciation: formation of new species when a pre-existing species splits
• Allopatric speciation: members of a species migrate to a new area and interbreeding becomes impossible due to geographical isolation
• Sympatric speciation: two varieties of a species live in the same geographical area, but do not interbreed
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Adaptive Radiation
• Divergent evolution: speciation repeats so each new species evolves in different ways from one ancestral species
• Adaptive radiation: rapid group diverging
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Convergent Evolution
• Convergent Evolution: natural selection acts in the same way so in different parts of the world species become remarkably similar though are not closely related
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Rates of Evolution
• Gradualism: evolution proceeds very slowly, but large changes can gradually take place– Not supported by fossils which show
periods of stability and periods of major change
• Punctuated equilibrium: when new adaptations are made to cope with changed environmental conditions
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Transient Polymorphism
• Polymorphic: a population in which there are two alleles of a gene in a gene pool
• Transient Polymorphism: One allele is gradually replacing the other allele
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Balanced Polymorphisms
• Balanced polymorphism: two alleles of a gene persist indefinitely in the gene pool– For example: sickle cell anemia
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Humans as Primates
• Humas are classified as primates because they have the characteristic anatomical features– Grasping limbs, opposable thumb–Mobile arms that can transfer weight– Stereoscopic vision (forward facing eyes
on a flattened face with overlapping fields of view)
– Skull modified for upright posture
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Trends in Hominid Fossils
• Hominid family includes humans– Bipedalism: walking on two legs
• Evolutionary trends of hominids:– Increasing adaptation to bipedalism– Increasing brain size in relation to body
size
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Tracing Human Evolution
• Trace evolution mainly through fossils– Can be incomplete as only a tiny
proportion of animal bodies become fossilized
• Hominid fossils consist only of bones and teeth
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Hominid Diets and Brain Size
• Change to a diet that included meat corresponds with the start of an increase in brain size– Eating meat increases supply of protein,
fat and energy– Catching and killing prey is more difficult
than gathering plant foods, so natural selection will favor those with larger brains
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Genetic and Cultural Evolution
• Cultural Evolution: new methods, inventions or customs can be incorporated into what is passed on to later generations– Different from genetic evolution
because:• Does not involve changes in allele frequency
in a gene pool• Changes can occur in one lifetime, not over
generations• Nurture characteristics rather than nature
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Dating Fossils
• Fossils can be dated using radioisotopes (radioactive isotopes of chemical elements)
• Half-life: times taken for the radioactivity to fall to half its original level