The Host Microbiome: Composition, Causation and Intervention · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

From microbiome snapshots to causal proof

Science · Microbiology · ages 23-24
Name ______________________   Date ____________

  1. Sequencing says one slice grew from 10 to 20 percent. Why stay cautious?

    • Percentages always sum to a whole, so other slices may have shrunk
    • The sequencer may have missed that species entirely, hiding its true share
    • Percentages above 10 are unreliable

  2. What does a microbiome name?

    • One disease-causing species
    • The whole community at one site
    • The nutrients that resident microbes consume

  3. Resident microbes defend their niche by occupying sites and nutrients, leaving invaders little room.

    Circle one:   True   False

  4. Which design separates a microbiome cause from a consequence?

    • Randomized transfer of defined microbes with a comparison group
    • Sequencing the same patients deeper
    • A larger snapshot survey

  5. Sick people carry a different gut mix than healthy people. What may you conclude so far?

    • The sickness causes the mix
    • The mix causes the sickness
    • Only that sickness and mix travel together so far

  6. A transplant trial fixed no endpoint in advance and reports the one marker that moved. What is the flaw?

    • The strain was not named
    • Cherry-picking an endpoint after the fact weakens the claim
    • Transplants need no comparison group

  7. A probiotic claim is convincing once it shows a shifted profile after treatment, with no strain or control details.

    Circle one:   True   False

  8. Patients improve equally whether or not the strain engrafted. What do you conclude?

    • Engraftment proof is unnecessary
    • The microbes caused the improvement despite the engraftment result
    • The microbes were likely passengers; something else helped
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Answer key

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

From microbiome snapshots to causal proof W1-mt_-F8lNccQCU-s1

  1. Percentages always sum to a whole, so other slices may have shrunk · Relative shares move together, so read the whole mix.
  2. The whole community at one site · It is the community census, never a single species.
  3. True · Protective crowding is part of normal defense, not contamination.
  4. Randomized transfer of defined microbes with a comparison group · Changing the microbes while holding the rest steady tests the arrow.
  5. Only that sickness and mix travel together so far · A snapshot cannot point the arrow; habitat change explains the same pattern.
  6. Cherry-picking an endpoint after the fact weakens the claim · Pre-chosen endpoints stop the team from reporting whatever wiggled.
  7. False · Without strain, engraftment proof, endpoint, and controls the story stays correlation.
  8. The microbes were likely passengers; something else helped · Causation needs improvement tied to engraftment, not attention or care.
Worksheet · LightMySky