Protists: the eukaryotes that are not plants, animals or fungi · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Protists and the origins of organelles

Science · Organisms & Life Processes · ages 18-19
Name ______________________   Date ____________

  1. Which finding most directly links chloroplast ancestry to cyanobacteria?

    • The host has a nucleus surrounded by membranes
    • Plastid genes resemble cyanobacterial genes
    • The host moves through water using long flagella

  2. Which ancestral partner gave rise to mitochondria?

    • A bacterium living inside a host
    • A piece of the host's external cell wall
    • A virus that replaced the host's nucleus

  3. All protists are single-celled organisms.

    Circle one:   True   False

  4. Which pairing correctly connects protist lifestyles with the structures they use?

    • Pseudopodia capture prey; chloroplasts capture light
    • Chloroplasts capture prey; food vacuoles capture light
    • Food vacuoles capture light; pseudopodia digest prey

  5. Which acquisition history is supported by comparisons across eukaryotic lineages?

    • Every lineage had plastids before mitochondria first appeared
    • Each lineage acquired its mitochondria separately from viruses
    • Their shared ancestor had mitochondria; plastids arose later

  6. A proposed group includes an ancestor shared by some protists and animals, but excludes animals. Why is it not a clade?

    • Members of a clade must all use an identical feeding method
    • It omits descendants of the included ancestor
    • Members of a clade must all have a single-celled body

  7. A protist lacks mitochondria, but close relatives have reduced mitochondria. A student concludes its lineage split before mitochondrial acquisition. Which alternative must be considered?

    • It later lost mitochondria inherited from an ancestor
    • Its relatives formed mitochondria directly from their cell walls
    • Its present organelles reveal every structure its ancestors possessed

  8. A protist's plastid has four surrounding membranes and a remnant algal nucleus. Which origin best fits these combined features?

    • The host folded its own membranes without acquiring another cell
    • The host acquired a cyanobacterium that already contained an algal nucleus
    • The host acquired an alga that already had a plastid
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Answer key

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

Protists and the origins of organelles W1-mt_CHb8H727nW-s1

  1. Plastid genes resemble cyanobacterial genes · Gene similarities connect plastids to cyanobacteria. The host's nucleus or movement structures do not identify the plastid ancestor.
  2. A bacterium living inside a host · Mitochondria descended from bacterial partners related to alphaproteobacteria, which became integrated into host cells.
  3. False · Many protists are single-celled, but colonial and multicellular forms also occur.
  4. Pseudopodia capture prey; chloroplasts capture light · An amoeba uses pseudopodia to surround prey. Photosynthetic protists capture light energy in chloroplasts.
  5. Their shared ancestor had mitochondria; plastids arose later · Comparative evidence supports mitochondria in the last common eukaryotic ancestor and later plastid origins in particular branches.
  6. It omits descendants of the included ancestor · A clade contains an ancestor and all its descendants. This proposed group excludes animal descendants of its included ancestor.
  7. It later lost mitochondria inherited from an ancestor · Present absence may result from later loss. It does not establish that the lineage separated before mitochondrial acquisition.
  8. The host acquired an alga that already had a plastid · Extra membranes together with an algal nuclear remnant support secondary endosymbiosis: uptake of an alga already containing a plastid.
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