Taxonomy, the three domains and what a species name encodes · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Naming life by its family tree

Science · Genetics & Evolution · ages 16-17
Name ______________________   Date ____________

  1. In the three-domain system, the domains of cellular life are Bacteria, Archaea and Eukarya.

    Circle one:   True   False

  2. Which statement about taxonomic ranks is accurate?

    • They mark levels in a nested classification.
    • They date the group's common ancestor.
    • They require every member to have the same appearance.

  3. In the hypothetical species name Nera luma, what is Nera?

    • A species
    • The genus
    • A kingdom

  4. Two hypothetical animal lineages gain flight independently. A student uses flight alone to classify them as each other's closest relatives. Which conclusion is justified?

    • Separate flight origins rule out shared ancestry.
    • Similar flight function makes inherited anatomy irrelevant to classification.
    • Flight alone does not establish that they are closest relatives.

  5. Which group meets the definition of a clade?

    • An ancestor and all its descendants
    • An ancestor and only its similar-looking descendants
    • Organisms sharing one habitat

  6. Why was the older grouping of all prokaryotes revised in the three-domain system?

    • Cell size alone established that all prokaryotes had the same recent ancestor.
    • Ribosomal RNA revealed deep differences between the two groups.
    • Their shared lack of a nucleus ruled out differences in molecular sequences.

  7. Suppose a genus forms a clade. Species A and B are inside it; species C is outside it but in the same domain. A and B share a more recent common ancestor than A and C.

    Circle one:   True   False

  8. Several independent gene comparisons contradict a genus's proposed ancestry. What is the best response?

    • Retain the grouping because an established name cannot change.
    • Reject the comparisons because genes cannot inform classification.
    • Reassess the grouping using the combined evidence.
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Naming life by its family tree W1-mt_12ucjuHtHE-s1

  1. True · These are the domain names in that classification system. Naming the domains does not settle their deepest branching relationships.
  2. They mark levels in a nested classification. · Ranks describe broad and narrow levels of classification. They do not give ancestor dates or require identical appearance.
  3. The genus · Nera is the genus; luma is the specific epithet. Together, Nera luma forms the species name.
  4. Flight alone does not establish that they are closest relatives. · Independently gained flight shows convergence. It cannot by itself establish that the lineages are each other's closest relatives. Older shared ancestry remains possible, and inherited anatomy and other evidence can help test relationships.
  5. An ancestor and all its descendants · A clade includes the ancestor and every descendant. Leaving out descendants because they look different breaks that definition.
  6. Ribosomal RNA revealed deep differences between the two groups. · Bacteria and Archaea both lack a nucleus, but ribosomal RNA comparisons revealed deep differences that supported distinguishing them.
  7. True · Because this genus is a clade, its ancestor joins A and B after the lineage leading to C has separated.
  8. Reassess the grouping using the combined evidence. · An ancestry-based grouping is testable. Consistent conflicting evidence calls for reassessment, rather than keeping the grouping just because it has an established name.
Worksheet · LightMySky