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General Biology: Fossil Dating, Taxonomy, and Phylogenetics

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  • What does relative dating tell us about fossils in stratum A versus stratum C?
    Fossils in stratum A are older than those in stratum C because lower strata are deposited earlier in geological time.
  • What can be said about the absolute age of fossils in stratum B?
    The absolute age of fossils in stratum B is between the ages of fossils in strata A and C, based on their position.
  • What is the half-life of Carbon-14 and what isotope does it decay into?
    Carbon-14 has a half-life of 5730 years and decays into the stable isotope Nitrogen-14.
  • If a fossil has 12.5% of its original Carbon-14 remaining, how old is it?
    It is approximately 17,190 years old, because 12.5% corresponds to three half-lives (3 × 5730 years).
  • How much Carbon-14 remains after 11,500 years if the organism started with 30 grams?
    After 11,500 years (about two half-lives), 7.5 grams of Carbon-14 remains (30 g → 15 g → 7.5 g).
  • Which Linnean taxonomic rank is the most general and which is the most specific?
    Domain is the most general rank, and Species is the most specific rank.
  • If two species belong to the same family, what other taxonomic ranks must they share?
    They must also belong to the same order, class, phylum, kingdom, and domain.
  • In a phylogenetic tree, what does a blue dot on a branch represent?
    The blue dot represents a common ancestor from which descendant taxa evolved.
  • Are taxa C and D sister taxa in a phylogenetic tree?
    Yes, C and D are sister taxa because they share an immediate common ancestor.
  • Are taxa F and G sister taxa in a phylogenetic tree?
    Yes, F and G are sister taxa as they share a recent common ancestor.
  • Are taxon B and the group containing C and D sister taxa?
    Yes, B and the group containing C and D are sister taxa sharing a common ancestor.
  • What is the basal taxon in a phylogenetic tree?
    The basal taxon is the lineage that diverged earliest from the common ancestor, often at the base of the tree.
  • What defines a monophyletic group in phylogenetics?
    A monophyletic group includes an ancestor and all of its descendants.
  • What defines a paraphyletic group?
    A paraphyletic group includes an ancestor and some, but not all, of its descendants.
  • What defines a polyphyletic group?
    A polyphyletic group includes taxa from different ancestors, excluding their most recent common ancestor.
  • Why might a group be incorrectly classified as polyphyletic?
    Because of convergent evolution or incomplete data leading to grouping unrelated taxa based on similar traits.
  • What is wrong with a group that excludes some descendants of a common ancestor?
    It is paraphyletic because it does not include all descendants.
  • What is wrong with a group that combines taxa from different ancestors?
    It is polyphyletic because it does not include the most recent common ancestor.
  • How do shared derived characters help construct a phylogenetic tree?
    They identify evolutionary relationships by showing traits that evolved in common ancestors and define clades.
  • What is the significance of sister taxa in evolutionary biology?
    Sister taxa share an immediate common ancestor and are each other's closest relatives.