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Unit 6 Study Guide

This page was made to help you study for the Unit 6 FRQs on Wednesdays. It includes notes and questions sourced from the slides and review videos Mr. Padilla recommended to us.

Question

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A student claims that the Miller-Urey experiment proved that life first evolved in the atmosphere of early Earth. Which statement is the best correction?

Key Notes

High-yield Unit 6 review points to scan while the current question stays at the top of the page.

  1. 1. Archean Eon
    • About 4.0 to 2.5 billion years ago.
    • Early atmosphere was mostly carbon dioxide, water vapor, and methane.
    • Earth formed about 4.5 billion years ago.
    • It took about 500 million years for the crust to solidify.
    • The oldest microorganism fossils in the notes are about 3.5 billion years old, found in western Australia.
    • Early life was dominated by prokaryotes.
    • One of the earliest major divergences was Bacteria versus Archaea.
  2. 2. Stromatolites
    • Stromatolites are fossilized bacterial mats.
    • They are important because they are fossil evidence of very early prokaryotic life.
    • If you see stromatolites in a question, think ancient prokaryotes, bacterial mats, and early Earth evidence for life.
  3. 3. Origin of Life: Chemical Evolution
    • The notes give a four-step model: abiotic synthesis of small organic molecules, monomers joined to form polymers, origin of self-replicating molecules, and packaging into protobionts.
    • Abiotic means nonliving or nonbiological.
    • A monomer is a small building block.
    • A polymer is a larger molecule made of monomers.
    • A protobiont is an aggregate of abiotically produced molecules that maintains some internal chemistry and shows some life-like properties.
  4. 4. Protobionts
    • Not true cells yet.
    • They are membrane-like collections of molecules.
    • They matter because they are a possible bridge between chemistry and the first cells.
    • They may show an internal chemical environment, simple metabolism-like behavior, and some organization.
  5. 5. RNA World Hypothesis
    • RNA is proposed to have come before DNA because it can both store information and have catalytic properties.
    • DNA stores information very well, but it is not catalytic in the same way.
    • Protein enzymes are catalytic, but proteins do not self-template genetic information.
    • RNA is a logical early candidate because it combines both jobs better than DNA or proteins alone.
  6. 6. Miller-Urey Experiment
    • Tried to simulate early Earth conditions.
    • Showed that organic molecules could form from inorganic starting materials under assumed ancient Earth conditions.
    • It did not create life.
    • It supports the idea that the building blocks of life could form naturally before cells existed.
  7. 7. Hydrothermal Vent Hypothesis
    • Hydrothermal vents are emphasized as a possible site where simple compounds became more complex.
    • Vents matter because they provide an energy source, mineral surfaces, a chemically rich environment, and a possible protected environment for early reactions.
  8. 8. Endosymbiotic Theory
    • A larger ancestral cell engulfed smaller prokaryotes.
    • Those engulfed prokaryotes became mitochondria and chloroplasts.
    • This explains how eukaryotic cells gained complex organelles.
    • Endosymbiosis is strongly tied to the success and diversification of eukaryotes.
  9. 9. Great Oxygenation Event
    • About 2.5 to 2.0 billion years ago.
    • Cyanobacteria evolved and produced large amounts of oxygen through photosynthesis.
    • Oxygen reacted with atmospheric methane and changed Earth permanently.
    • This eventually led to a more oxygen-rich atmosphere and blue skies.
    • Red bands and banded iron formations are evidence because oxygen oxidized iron in rocks.
  10. 10. Cyanobacteria
    • Early photosynthetic prokaryotes.
    • About 2.7 billion years ago in the notes.
    • First organisms to photosynthesize and release oxygen at a major scale.
    • They were crucial to atmospheric change.
  11. 11. Darwin's Research / HMS Beagle
    • Darwin traveled on the HMS Beagle.
    • He collected plants and animals from South America.
    • He noticed that organisms were adapted to different environments.
    • The Galapagos Islands were especially important for his thinking about geographic distribution and adaptation.
  12. 12. Paleontology
    • Paleontology means study of fossils.
    • Fossils are remains or traces of past organisms, usually in sedimentary rock.
    • Fossils helped build the groundwork for Darwin's ideas.
  13. 13. Catastrophism
    • Associated with Georges Cuvier.
    • It is the idea that boundaries between rock strata reflect catastrophic events.
    • It was important historically, but it did not explain gradual change over long time scales as well as gradualism did.
  14. 14. Gradualism
    • Gradualism means profound change can happen through the cumulative effects of slow, continuous processes.
    • Associated with Hutton and Lyell.
    • This influenced Darwin because if Earth changes slowly over immense time, life could also change over immense time.
  15. 15. Adaptation
    • An adaptation is an inherited trait that improves survival or reproduction in a particular environment.
    • Darwin connected adaptation with the formation of new species.
    • Galapagos finches are the classic example because different beaks match different food sources and different niches.
  16. 16. Natural Selection
    • More individuals are born than can survive.
    • Individuals vary.
    • Some variation is heritable.
    • Individuals with traits better suited to the environment leave more offspring.
    • Over generations, favorable alleles become more common.
    • Natural selection acts on individual phenotypes, but populations evolve.
  17. 17. Descent with Modification
    • Present-day species descended from ancestral species.
    • This explains both the unity of life through shared ancestry and the diversity of life through branching change over time.
  18. 18. Darwin vs. Wallace
    • Darwin developed his ideas for years.
    • In 1858, Alfred Russel Wallace sent Darwin a manuscript with a similar theory of natural selection.
    • Darwin then moved quickly to publish On the Origin of Species in 1859.
  19. 19. Relative Dating
    • In sedimentary rock, deeper strata are generally older.
    • A fossil lower in the strata is usually older than one above it.
    • This does not give exact age, only relative age.
  20. 20. Evidence for Evolution
    • The notes reinforce fossils, comparative anatomy, DNA and molecular evidence, biogeography, and observed evolutionary change.
    • Resistance in bacteria and viruses is a direct modern example.
  21. 21. Antibiotic Resistance / Drug Resistance
    • Antibiotics do not make bacteria try harder.
    • They create a selection pressure.
    • Susceptible bacteria die first.
    • Resistant bacteria survive and reproduce.
    • The same logic applies to drug-resistant HIV.
    • This is a modern, direct example of natural selection.
  22. 22. DNA as Evidence of Common Ancestry
    • DNA and the genetic code reflect shared ancestry.
    • Comparing DNA sequences helps show how species are related.
    • More similar DNA usually suggests a more recent common ancestor.
  23. 23. Mutation
    • A mutation is a change in gene structure producing a variant form that may be inherited.
    • Mutation is the ultimate source of new genetic variation.
  24. 24. Cladogram
    • A cladogram is a branching diagram that represents a hypothesis about evolutionary relationships.
    • It shows patterns of common ancestry, not just surface similarity.
    • Relatedness depends on how recent the common ancestor is, not how close two species are drawn on the page.
  25. 25. Phylogenetic Tree
    • Shows evolutionary relationships among species or groups.
    • Nodes represent common ancestors.
    • Branches nearest the tips represent more recent lineages.
    • Branches farther from the root are not more advanced; they just represent different lineages.
  26. 26. LUCA
    • LUCA stands for Last Universal Common Ancestor.
    • It is the hypothesized common ancestral cell from which Bacteria, Archaea, and Eukarya originated.
  27. 27. Homologous Genes
    • Genes shared by species because they were inherited from a common ancestor.
    • Molecular homology is powerful evidence for common descent.
  28. 28. Orthologous Genes
    • Orthologous genes are homologous genes that diverged after a speciation event.
    • Their main function is often conserved.
    • These are especially useful for comparing related species.
  29. 29. Taxonomy
    • Taxonomy is the ordered division of organisms into categories based on characteristics.
    • Linnaeus's system is still useful because it gives binomial nomenclature and hierarchical classification.
  30. 30. Binomial Nomenclature
    • Two-part scientific name: genus and specific epithet.
    • The genus is capitalized.
    • The full species name is italicized or latinized.
    • The specific epithet alone is not the full species name.
  31. 31. Clade
    • A clade includes an ancestral species and all of its descendants.
    • Clades are nested within larger clades.
    • A valid clade must be monophyletic in AP Biology language.
  32. 32. Outgroup
    • An outgroup is closely related to the ingroup but not part of it.
    • It helps identify which characters are shared primitive and shared derived.
    • If both outgroup and ingroup have a trait, that trait is usually considered primitive.
  33. 33. Shared Derived Characters
    • Traits that evolved in a lineage after it split from the outgroup.
    • These are the most useful for building cladograms.
    • Examples from the character table include vertebral column, hinged jaws, four walking legs, amniotic egg, and hair.
  34. 34. Molecular Homology
    • Systematists compare DNA sequences with computer and math tools.
    • Sequence similarity helps estimate relatedness.
    • Similarity from convergent evolution can mislead if you only look at anatomy.
  35. 35. Convergent Evolution
    • Unrelated organisms can evolve similar traits because they face similar selective pressures.
    • Similarity does not always mean close relatedness.
    • The mole example in the notes is useful for this.
  36. 36. Biological Species Concept
    • A species is a group of organisms that can interbreed and produce fertile offspring.
    • Its main focus is reproductive isolation.
  37. 37. Limits of the Biological Species Concept
    • It does not work as well for fossils.
    • It does not work as well for asexual organisms.
    • It also struggles with some subspecies and geographically variable populations.
  38. 38. Other Species Concepts
    • Morphological species concept is based on physical traits.
    • Recognition species concept is based on successful mating signals.
    • Cohesion species concept is based on discrete phenotypic entities.
    • Ecological species concept is based on niche, role, or function.
    • Evolutionary species concept is based on lineage and evolutionary history.
  39. 39. Prezygotic Barriers
    • Prevent fertilization from happening.
    • Habitat isolation.
    • Behavioral isolation.
    • Temporal isolation.
    • Mechanical isolation.
    • Gametic isolation.
  40. 40. Postzygotic Barriers
    • Fertilization happens, but offspring problems occur.
    • Reduced viability.
    • Reduced fertility.
    • Hybrid breakdown.
  41. 41. Allopatric Speciation
    • Gene flow is interrupted by geographic isolation.
    • Physical barriers split populations.
    • Over time, mutation, drift, and selection can make them reproductively isolated.
  42. 42. Sympatric Speciation
    • Speciation without geographic separation.
    • It can happen through nonrandom mating or chromosomal changes.
    • It is often associated with polyploidy in plants, though the slide emphasizes chromosomal changes generally.
  43. 43. Gradualism vs. Punctuated Equilibrium
    • Gradualism means species change slowly over time.
    • Punctuated equilibrium means long periods of little change interrupted by short bursts of rapid change.
  44. 44. Sexual Selection
    • A form of natural selection for mating success.
    • It can lead to sexual dimorphism, where males and females differ in secondary sex traits.
  45. 45. Intrasexual Selection
    • Competition within one sex for access to mates.
    • Usually male-male competition.
    • Think fighting, dominance, antlers, and large size.
  46. 46. Intersexual Selection
    • One sex chooses mates from the other sex.
    • Usually female choice in examples.
    • It often favors showy male traits.
  47. 47. Reproductive Handicap of Sexual Reproduction
    • Sexual reproduction often produces fewer reproductive descendants than asexual reproduction.
    • Sexual reproduction increases genetic variation, which can help with disease resistance and adaptation.
  48. 48. r-selected vs. K-selected
    • r-selected organisms are small, fast growing, common in unstable environments, produce many offspring, and provide low parental care.
    • K-selected organisms are larger, slower growing, common in stable environments, produce fewer offspring, and provide more parental care.
  49. 49. Population Genetics
    • Study of how populations change genetically over time.
    • It combines Mendelian genetics with Darwinian evolution.
    • Populations, not individuals, are the units of evolution.
  50. 50. Microevolution
    • Microevolution is change in the genetic makeup of a population from generation to generation.
    • It is usually measured as changes in allele frequencies.
  51. 51. Gene Pool
    • The total aggregate of genes in a population at one time.
    • It includes all alleles at all loci in all individuals.
  52. 52. Allele Frequency
    • The proportion of a certain allele in the gene pool.
    • Evolution at the population level is basically a change in allele frequency over time.
  53. 53. Modern Synthesis
    • Combines Darwin's natural selection, Mendelian genetics, and population genetics.
    • It focuses on populations as the units of evolution.
  54. 54. Genetic Drift
    • Random change in allele frequency.
    • Strongest in small populations.
    • It is not the same as natural selection because it is based on chance, not fitness advantage.
  55. 55. Bottleneck Effect
    • A population is suddenly reduced in size.
    • The surviving gene pool is a random sample of the original.
    • Genetic variation usually drops.
    • Future allele frequencies may look very different from the original population.
  56. 56. Founder Effect
    • A small subgroup leaves a population and starts a new one.
    • The new population may have allele frequencies very different from the source population just by chance.
  57. 57. Selection Patterns
    • Directional selection favors one extreme and shifts the mean.
    • Stabilizing selection favors the intermediate phenotype and removes extremes.
    • Disruptive selection favors both extremes and selects against the average phenotype.
  58. 58. Hardy-Weinberg
    • It is a null model describing what a population looks like if it is not evolving.
    • Key equations: p + q = 1 and p^2 + 2pq + q^2 = 1.
    • p is the frequency of the dominant allele and q is the frequency of the recessive allele.
    • p^2 is homozygous dominant, 2pq is heterozygous, and q^2 is homozygous recessive.
    • Conditions: very large population, random mating, no mutation, no migration or gene flow, and no natural selection.

Don't Mix These Up

  • Natural selection is nonrandom; genetic drift is random.
  • Individuals are selected; populations evolve.
  • Homologous traits suggest common ancestry; analogous traits usually reflect convergent evolution.
  • Cladogram means a hypothesis of relationships; taxonomy means naming and classifying organisms.
  • Prezygotic barriers prevent fertilization; postzygotic barriers act after fertilization.
  • Allopatric speciation uses geographic isolation; sympatric speciation does not require a physical barrier.
  • Miller-Urey supports abiotic formation of organic molecules; it does not prove exactly how life began.

Red Terms to Know Cold

  • Archean Eon
  • Stromatolites
  • Great Oxygenation Event
  • Cyanobacteria
  • Paleontology
  • Gradualism
  • Cladogram
  • Phylogenetic Tree
  • Homologous Genes
  • LUCA
  • Taxonomy
  • Binomial
  • Clade
  • Outgroup
  • Sexual Selection
  • Intrasexual Selection
  • Reproductive Handicap
  • r-selected
  • K-selected
  • Allopatric
  • Sympatric
  • Microevolution
  • Population Genetics
  • Genetic Drift
  • Bottleneck Effect
  • Founder Effect