Option D D1 Origins of Life on Earth
Pre-biotic Earth • The Solar System originated 4.57 BYA • The Earth originated 4.5 BYA • Formed by collisions of materials over 100 MY, creating a planet with oceans of liquid magma and a hot dense atmosphere • Cooling of the Earth took over 50 MY and the loss of the dense atmosphere
Pre-biotic Earth • Pre-Biotic Earth 4.4-4.0 BYA • Continents of solid rock forming • Oceans of water forming • High temperatures • High UV light levels • Reducing atmosphere (no O2) • Frequent storms with lightning • Life on Earth originated 3.5-4.0 BYA • Earliest organisms were bacteria • Stromatolites- banded domes of sediment strikingly similar to the layered mats constructed by colonies of bacteria and cyanobacteria
Spontaneous Origin of Life Topic D.1.1 Describe four processes needed for the spontaneous origin of life on Earth. • Chemical reactions to produce simple organic molecules, such as amino acids, from inorganic molecules, such as water, CO2, and ammonia. • Assembling of these simple organic molecules into polymers, for example, polypeptides from amino acids
Spontaneous Origin of Life • Formation of polymers that can self replicate- this allows inheritance of characteristics • Development of membranes, to form spherical droplets, with an internal chemistry different from the surroundings, including polymers that held genetic information.
Spontaneous Origin of Life • The product of these 4 processes would have been cell-like structures that natural selection could have operated on.
Miller and Urey Topic D.1.2. Outline the experiments of Miller and Urey into the origin of organic compounds. • In the 1920’s, A.I. Oparin of Russia and J.B.S. Haldane of Great Britain independently postulated that conditions on the primitive Earth favored chemical reactions that synthesized organic compounds from inorganic precursors present in the early atmosphere and seas. Oparin-Haldane Hypothesis • It cannot happen in the modern world, because the present atmosphere is rich in oxygen, the oxidizing atmosphere of today is not conducive to the spontaneous synthesis of complex molecules because the oxygen attacks chemical bonds, extracting electrons.
Miller and Urey • In 1953, Stanley Miller and Harold Urey tested the Oparin-Haldane Hypothesis using the conditions of pre-biotic Earth.
A. A warm flask of water simulated the primeval sea B. The atmosphere consisted of H2O, H2, CH4, and NH3. C. Sparks were discharged to mimic lightning D. A condenser cooled the atmosphere, raining water and any dissolved compounds back to the miniature sea. E. As material circulated through the apparatus the solution in the flask changed from clear to murky brown F. After 1 week the contents of the flask were examined and found a variety of organic compounds including some amino acids that make up proteins of organisms.
What are their conclusions? • Organic compounds (amino acids) were formed from inorganic compounds. • Organic compounds could have existed on pre-biotic Earth. • Life might have arisen from non-living material.
Panspermia Topic D.1.3. State that comets may have delivered organic compounds to Earth. • Panspermia- the theory concerned with the arrival of material from outer space. • Hundreds of meteorites and comets hitting the early Earth brought with them organic molecules formed by abiotic reactions in outer space. • Extraterrestrial organic compounds, including amino acids, have been found in modern meteorites, and it seems likely that these bodies could have seeded the early Earth with organic compounds.
Origin of Life 4. Discuss possible locations where conditions would have allowed the synthesis of organic compounds. • Miller and Urey’s experiment suggest organic compounds could have synthesized in Pre-Biotic Earth. • Lightning, high temps, oceans forming, Reducing atmosphere
Origin of Life • There are hydrothermal vents deep in the oceans, with chemicals welling up from the rocks below. • Around these vents, there are unusual chemical conditions, which might have allowed the spontaneous synthesis of the first organic compounds.
Origin of Life • Panspermia- Tests have shown that meteorites do contain organic compounds and proto-cells. • Pre-biotic earth was bombarded with meteorites, comets and interplanetary dust, which might have brought organic compounds that became organized into the first living organisms.
RNA Topic D.1.5. Outline two properties of RNA that would have allowed it to play a role in the origin of life. • RNA is thought to have served as the first genes, not DNA. • DNA RNA Proteins: the mechanisms for this is too complicated to have evolved all at once. • Genes cannot be replicated without enzymes, and enzymes cannot be made without genes. • The first genes were short strands of RNA that began self-replicating in the prebiotic world.
RNA • RNA also has been shown to act as an enzyme, called ribozyme. • RNA has catalytic properties • RNA can catalyze the formation of more RNA (rRNA, tRNA, and mRNA) • RNA can bind amino acids and form peptide linkages • RNA can transcribe into DNA using reverse transcriptase
Protobionts Topic D.1.6 State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surrounding. • This is biochemical evolution. • Coacervate droplets self-assembles when a solution of polypeptides, nucleic acids, and polysaccharides is shaken. • Coacervates can contain polynucleotides (RNA) • Assembly of chains of amino acids can form • Formation of proteins • Alignment of lipids and the formation of a membrane • Synthesis of ATP and anaerobic respiration • Asexual reproduction
Prokaryotes Topic D.1.7 Outline the contribution of prokaryotes to the creation of an oxygen rich atmosphere. • The first organisms on earth were photosynthetic prokaryotes. • Oxygen is a waste product of photosynthesis. • Oxygen concentrations build up over time
First Humans Extinction of dinosaurs 0 Cenozoic Origin of reptiles Plants colonize land Mesozoic Paleozoic 500 Origin of multicellular organisms (oldest animal fossils) 1500 Oldest eukaryotic fossils Precambrian 2500 Accumulation of atmospheric oxygen from photosynthetic cyanobacteria Oldest prokaryotic fossils 3500 Origin of life? Earth cool enough for crust to solidify 4500 Origin of Earth
Endosymbiotic Theory Topic D.1.8 Discuss the endosymbiotic theory for the origin of eukaryotes. • Eukaryotic cells contain membrane bound organelles. • According to the Endosymbiotic Theory proposed by Lynn Margulis of the University of Massachusetts, both the Mitochondria and Chloroplasts have evolved from independent prokaryotic cells, which were taken into a larger heterotrophic cell by endocytosis. • Instead of being digested, the cells were kept alive and continued to carry out aerobic respiration and photosynthesis.
Endosymbiotic Theory • The characteristics of mitochondria and chloroplasts that support the Endosymbiotic Theory are: • Similar in size to Bacteria • They grow and divide like cells. • They have a circular naked loop of DNA. • They synthesize some of their own proteins using 70S ribosomes. • They have double membranes, as expected when cells are taken into a vesicle by endocytosis. • Reproduce by binary fission. • Cristae are similar to mesosomes of prokaryotes. • Thylakoids are similar to structures containing chlorophyll in photosynthetic prokaryotes.
Allele Frequency and Gene Pool Topic D.2.1 Define Allele Frequency and Gene Pool. • Allele Frequency- is 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 • Usually expressed as a percentage or a proportion • Gene Pool- is all the genes in an interbreeding population.
Evolution Topic D.2.2 State that evolution involves a change in allele frequency in a population’s gene pool over a number of generations.
Species Topic D.2.3 Discuss the definition of a species. • What is a species? • A species is a potentially interbreeding population having a common gene pool. • Typological species concept- species are static, nonvariable assemblages of organisms that conform to a common morphological plan • Plato and Aristotle • Today we use it as the type specimen • Problems: • What are type characteristics?
Species • Morphological species concept- Species are distinguished from each other by their morphological characteristics. • Useful for fossils • Problems: • Sexual dimorphism • Cryptic Species • Geographic variation
Species • Biological species concept- a group of actually or potentially interbreeding populations, with a common gene pool, which are reproductively, isolated from other such groups. Ernst Mayr (1963) • Problems: • Sibling species- species that cannot interbreed, but show no significant differences in appearance. • Hybridization between different species • Species that only reproduce asexually • Fossils
Species • Phylogenetic species concept- monophyletic and genomically coherent clusters of individual organisms that are descended from a single ancestral taxon and show a high degree of overall similarity in many independent characteristics, diagnosable by a discriminative phenotypic property. A species is a monophyletic group. • Problems: • DNA, Amino acids, or morphology • Different techniques for analyzing sequence data • Gene tree vs. Species tree
Gene Pools Topic D.2.4 Describe three examples of barriers between gene pools. Topic D.2.6 Compare Allopatric and Sympatric Speciation. • The formation of a new species is called speciation. • New species are formed when a pre-existing species splits. • This usually involves the isolation of a population of the remainder of its species and thus the isolation of its gene pool. • The isolated population will gradually diverge from the rest of the species if natural selection acts differently on it. • Eventually the isolated population will not be able to interbreed with the rest of the species—it has become a new species.
Speciation • Allopatric speciation- species are isolated geographically. • Geographic Isolation- When members of a species migrate to a new area, forming a population that is geographically isolated from the rest of the population. • Migration- members of a species move to a new location that is geographically isolated from the original territory. • The Galapagos Finches • Lava lizards in the Galapagos • Adaptive radiation- the evolution of many diversely adapted species from a common ancestor.
Speciation • Sympatric speciation- species are not isolated geographically. A subpopulation becomes reproductively isolated in the midst of its parent population.
Speciation • Behavioral Isolation • Example: Apple Maggot Fly (Rhagoletis pomonella) • It originally laid its eggs on Hawthorn fruits, but some individuals started to infest non-native apple trees as well. The fruits ripen at different times, thus the adults emerge and mate at different times. • Now you have two separate breeding populations of the apple maggot fly. There are differences in allele frequencies, but they have not been classified as different species as of yet.
Speciation • Hybrid Infertility- barriers between gene pools- often due to polyploidy. • Polyploidy- extra sets of chromosomes • Plants may evolve into new species in one generation by a polyploid event. • Autopolyploid- More than one set of chromosomes evolves from a single species. • Allopolyploid- More than one set of chromosomes evolves from different species.
Speciation Topic D.2.5 Explain how polyploidy can contribute to speciation. • Rumex- most species have 20 chromosomes. • Rumex obtusifolius has 40 • Rumex crispus has 60 • Rumex hydrolapathum has 200
Speciation Topic D.1.7 Outline the process of adaptive radiation. • Adaptive Radiation- process in which many related species evolve from one ancestor • Example: Darwin’s Finches • One finch or mating pair makes it to an island • They have no predetors and unlimited resources. • They are able to reproduce as much as possible
Speciation • Variation exists and they can spread out to other niches. • They adapt to fill all the niches.
Speciation 8. Compare convergent and divergent evolution. • Convergent Evolution- similar structures or form but not closely related • Shark and porpoise • Divergent Evolution- 2 or more related species that look different because of habitat • All mammals have the same ancestor but look very different.
Evolution in Process • Homologous- similar feature from the same ancestor- limbs • Analogous- similar feature because of function but different ancestor- wing of bird and insect
Pace of Evolution Topic D.2.9 Discuss ideas on the pace of evolution including gradualism and punctuated equilibrium. • Gradualism is the slow change from one form to another. Punctuated equilibrium, however, implies long periods with no change and short periods of rapid evolution. Mention could be made of the effects of volcanic eruptions and meteor impacts in affecting evolution on Earth.
Pace of Evolution • Over long periods of time, many advantageous alleles will appear and spread through a species. These micro-evolutionary steps together constitute macroevolution. • Eventually the amount of change becomes so great that the species is no longer the same and one species have evolved into another. • Gradualism- slow change from one form to another. Evolution proceeds slowly, but over long periods of time larger changes can gradually take place. This does not fit with the fossil record.
Pace of Evolution • The fossil record shows periods of periods of stability, with fossils showing little change, followed by periods of sudden major change. • The periods of stability may be due to equilibrium where living organisms become well adapted to their environment so natural selection acts to maintain their characteristics. • The periods of sudden change that punctuated the equilibrium may correspond with rapid environmental change, caused for example by volcanic eruptions or meteor impacts. • New adaptations would be necessary to cope with new environmental conditions, hence strong directional selection and rapid evolution—Punctuated equilibrium.
Transient Polymorphism Topic D.2.10 Describe one example of transient polymorphism. • Populations of ladybug that changed from having red wings with black spots to black wings are an example of transient polymorphism.
Adalia bipunctata • Adalia bipunctata- Ladybeetle- 2 spotted small beetle, which usually has 2 small black spots on its red wings. • The red is a type of aposematic coloration. Melanic forms also exist, with solid black wings. • The melanic forms absorb heat more efficiently and therefore have a selective advantage when sunlight levels are low. • The melanic form became more common in industrial areas of Britain, but declined again after the 1960’s. • If the air is dark with smoke the melanic form can warm up faster, but if there is no advantage to the melanin, then the Aposematic coloration is more of an advantage.
Balanced Polymorphism Topic D.2.11 Describe Sickle Cell Anemia as an example of Balanced Polymorphism. • Sickle cell anemia is an example of balanced polymorphism.
Hardy-Weinberg • Heterozygotes (HbA HbS) do not develop sickle cell anemia and are resistant to Malaria. • The sickle cell allele has increased in frequency to high levels in some areas. Parts of Africa, as many as 40% of the population are carriers of the sickle cell allele.
D3 Evidence for Evolution
Geographical Distribution Topic D.3.1 Describe the evidence for evolution as shown by the geographical distribution of living organisms, including the distribution of placental, marsupial, and monotreme mammals.
Wallace’s Line There are huge differences in the types of land animals that are found on either side of Wallace’s Line.
Placentals vs. Marsupials vs. Monotremes • Placental mammals are found on the Asian side • Mainly marsupial (pouched mammals) and monotreme (egg laying mammals- only three living monotreme species - the platypus, the short-beaked echidna, and the long-beaked echidna) mammals are found on the Australasian side.