1. Elicit students’ ideas about how to classify and organize living organisms through a card sort activity.

• Ask students:
  • What kinds of items do you organize or classify around the house, at school, or for sports or hobbies?
  • Why is it important to you to have those items organized?
• As students share their answers, keep track of their ideas in a visible place.
• Connect student ideas to scientific classification by asking:
  • Why is it important for scientists to classify and organize organisms? (Students’ answers will vary, but may include: having common terms to talk about the same organism, designate endangered species, understand broader patterns of how organisms are related to each other.)

• Pass out a set of Critter Cards to pairs or small groups of students.
• Organisms to include: manatee, hyrax, elephant, E. Coli., yeast, protozoa, algae, orchid, fern, earthworm, ant, sea star, kangaroo, lizard, snake, sea nettle, frog, eagle, crab, mouse, salmon, dog, lobster, and clam.
• Prompt students to use the guidelines below as they create groups for the organisms on the cards:
• Any kind of criteria can be used to form groups (for example legs/no legs), as long as all members agree on the grouping criteria.
• Each grouping should be given a name.
• Students should be prepared to explain their classification and naming system, and what features or criteria they used for grouping the organisms.   
• After students have decided on their organism groupings, prompt them to share with another partner or group; elicit a few groups to share with the whole class.

2. Project the tree of life from the OneZoom Tree of Life Explorer to show how scientists have organized all living organisms based on their evolutionary relationships.

• Zoom in and out of the tree to see different organisms and how they are grouped together on the tree.
• Ask students to point out what they notice about organisms that are close together on the tree versus far apart.
• Explain that the tree of life is one system of organizing organisms, both living and extinct, via fossil evidence. The groupings are based on scientists’ understanding of how closely related the organisms are, using evidence from the organisms’ anatomical features and, if possible, their genetic information (DNA and RNA).
  • Organisms that are hypothesized to be closely related are found close together on the tree because they share a recent common ancestor.
• Ask students:
  • How is the tree of life organization similar to or different from the grouping systems you used in the Critter Card Sort?
  • How did you use anatomical features in your sort?

3. Introduce the Linnaean system of scientific classification and explain how it is also based on the manner in which living organisms are related.

• Zoom out on the OneZoom Tree of Life Explorer to show the group names on the branches, such as eukaryotes.
  • Clicking on the name will show the scientific name, the number of species, and pictures of representative species.
• Explain that in addition to visually showing how organisms are related, scientists also use the tree of life to give names to groups of organisms. For example, Eukaryota represents one of the main three groupings of organisms: domains.
• Introduce the rest of the groupings under the Linnaean classification system, emphasizing how the naming system is hierarchical. Walk through a representative example to show how one organism concurrently belongs to multiple groups, such as a Western terrestrial garter snake (Thamnophis elegans):
  • Domain: Eukaryota
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Reptilia
  • Order: Squamata
  • Family: Colubridae
  • Genus: Thamnophis
  • Species: elegans

• Point out to students that Linnaean terms are in Latin, to standardize naming and communication about organisms across the world.

Apply the Linnaean system to the Critter Cards and microbes:

• Return to OneZoom and use the search box in the top right corner to locate some of the organisms on the Critter Cards.
  • Show how the elephant, hyrax, and manatee are each other’s closest relatives.
  • Show the representative microbes on the Critter Cards (Bacteria: Escherichia coli, Protozoa: Blepharisma japonicum, Algae: Dunaliella viridis) to demonstrate how microbes are spread across the tree of life.
• Refer to the scientific names that were on the Critter Cards and ask students to identify the level of grouping that is referred to (genus and species).
• Review the definition of microbes from the Introduction to Microbes and Human Body Systems activity: organisms that cannot be seen with the naked eye.
• Prompt students to compare this type of definition to the Linnaean system of classification by asking:
  • How is the term microbes similar to and different from the Linnaean system of scientific classification? (Possible responses: Similar because both are based on physical characteristics that are shared by organisms; different because many types of organisms are microscopic, it does not clarify if organisms are related to each other.)

4. To facilitate making connections to the focal organisms for the Misunderstood Microbes unit, prompt students to learn more about five of the main groups of microbes.

• Explain that students will work with a partner to engage with the Microbe Passports online interactive, which introduces five of the six main groups of microbes: bacteria, viruses, fungi, protozoa, and algae.
• Distribute and review the Introducing Microbes Note Tracker for students to keep track of their thinking and respond to synthesis questions that help students to connect microbes to scientific classification. Note that students need to hunt for the types of microbes listed on their Note Tracker, but may use the additional spaces for any others that they are interested in recording.
• Lead a debrief discussion. Use students’ responses to the synthesis questions on the tracker to solidify students’ understanding that microbes are found across the entire tree of life.