Pathogen Classification: Protists and Prions

Protists and prions challenge students to move beyond textbook definitions and confront misconceptions through direct observation and modeling. Active learning works because the abstract nature of these pathogens—alternating hosts, acellular propagation—demands tactile experiences that lectures alone cannot provide.

• Year 12
• Biology
• 4 activities
• 30 min–50 min

Learning Objectives

1. Compare the complex life cycles of protist pathogens, such as Plasmodium, with simpler infectious agents like viruses or bacteria.
2. Analyze how the unique protein-misfolding mechanism of prions leads to neurodegeneration, distinct from nucleic acid-based pathogens.
3. Explain the specific challenges in developing treatments for prion diseases due to their resistance to standard sterilization and antimicrobial agents.
4. Classify protists and prions based on their structure, genetic material (or lack thereof), and mode of replication.
5. Evaluate the public health impact of diseases caused by protists like malaria and sleeping sickness, considering their transmission vectors.

Jigsaw

⏱ 50 min·Small Groups

Jigsaw: Protist Life Cycles

Divide class into expert groups, each assigned a protist pathogen like Plasmodium or Trypanosoma. Groups create posters detailing life stages and disease mechanisms, then reform into mixed groups to teach peers. Conclude with a class timeline comparison. Provide templates for consistency.

Prepare & details

Analyze how the unique life cycles of protist pathogens contribute to their disease-causing potential.

Facilitation Tip: During the Jigsaw Activity, assign each expert group a distinct stage of the protist life cycle to ensure everyone contributes before returning to home groups.

Setup: Flexible seating for regrouping

Materials: Expert group reading packets, Note-taking template, Summary graphic organizer

• Understand
• Analyze
• Evaluate
• Relationship Skills
• Self-Management

Inquiry Circle

⏱ 30 min·Pairs

Chain Reaction Demo: Prion Propagation

Use dominoes or stacked paper clips to represent normal proteins; tip one to trigger a chain reaction mimicking misfolding. Students in pairs predict outcomes, run trials with variables like density, and draw parallels to prion diseases. Discuss resistance to antibiotics.

Prepare & details

Compare the mechanisms by which prions cause disease to those of other infectious agents.

Facilitation Tip: For the Chain Reaction Demo, use dominoes or paper clips to physically model prion conversion, pausing after each step to ask students to predict the next outcome.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Gallery Walk

⏱ 45 min·Small Groups

Gallery Walk: Pathogen Comparisons

Groups create comparison charts of protists, prions, bacteria, and viruses on posters covering structure, replication, and treatment. Class walks stations, adding sticky notes with questions or insights. Debrief with whole-class synthesis.

Prepare & details

Explain the challenges in treating diseases caused by prions compared to bacterial infections.

Facilitation Tip: In the Gallery Walk, post key terms and images at each station so students connect visuals to written explanations as they rotate.

Setup: Wall space or tables arranged around room perimeter

Materials: Large paper/poster boards, Markers, Sticky notes for feedback

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

Inquiry Circle

⏱ 40 min·Pairs

Case Study Debate: Treatment Challenges

Assign pairs real cases of malaria versus CJD. They research and debate pros/cons of treatments like antimalarials versus experimental prion therapies. Vote on most viable approaches and justify with evidence.

Prepare & details

Analyze how the unique life cycles of protist pathogens contribute to their disease-causing potential.

Facilitation Tip: During the Case Study Debate, provide a simple pro/con chart for students to fill as they research so arguments stay grounded in evidence.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Teaching This Topic

Teachers should avoid lumping protists and prions together as ‘weird microbes.’ Instead, emphasize their contrasting biology early: protists are eukaryotic parasites with complex development, while prions are misfolded proteins that hijack normal proteins. Research shows that students grasp non-living pathogens better when they first master living pathogen concepts, so sequence protists before prions. Use analogies carefully—some students overextend them—so always follow with precise biological language.

What to Expect

Students will articulate how protist life cycles and prion propagation differ from more familiar pathogens, explain why these differences matter for disease control, and apply classification criteria with confidence. Success shows in clear diagrams, reasoned debates, and accurate comparisons on assessment tasks.

Watch Out for These Misconceptions

Common Misconception

During the Chain Reaction Demo: Prion Propagation, students may assume prions are living because the chain reaction spreads.

What to Teach Instead

Use the physical domino or paper clip model to explicitly label each step as ‘conversion,’ not reproduction, and contrast it with mitosis in cells to redirect the misconception.

Common Misconception

During the Jigsaw Activity: Protist Life Cycles, students may treat protists like bacteria with simple binary fission.

What to Teach Instead

Have expert groups present their stage with a host/vector image and a timeline to highlight the multi-host complexity, then ask home groups to sequence posters to reveal the cycle’s sophistication.

Common Misconception

During the Gallery Walk: Pathogen Comparisons, students may think prion diseases can be cured with antibiotics.

What to Teach Instead

Point students to the treatment gap station where they see ‘no nucleic acid target’ listed, then prompt them to compare antibiotic action on the posters to reinforce why prions escape this treatment.

Assessment Ideas

Discussion Prompt

After the Case Study Debate: Treatment Challenges, pose a public health scenario and ask students to justify their ranking of threat using transmission, treatment, and spread data they gathered during the debate prep.

Quick Check

During the Jigsaw Activity: Protist Life Cycles, give each home group a set of mixed pathogen cards and ask them to sort protists from bacteria and viruses based on life cycle clues before explaining their choices.

Exit Ticket

After the Chain Reaction Demo: Prion Propagation, have students write one structural difference between prions and protist pathogens and explain why that difference makes prions harder to treat, collecting responses as they leave.

Extensions & Scaffolding

• Challenge: Ask students to design a public health campaign targeting either a protist or prion disease, citing life cycle or propagation evidence.
• Scaffolding: Provide partially completed life cycle diagrams or prion propagation chains with missing steps for students to fill in.
• Deeper exploration: Invite students to research a neglected tropical protist disease and present how climate change may alter its geographic range.

Key Vocabulary

Protist	A diverse group of eukaryotic microorganisms, some of which are pathogenic and cause diseases like malaria or sleeping sickness.
Prion	An infectious agent composed solely of misfolded protein, lacking genetic material, that causes fatal neurodegenerative diseases.
Vector	An organism, often an insect like a mosquito or tsetse fly, that transmits a pathogen from one host to another.
Neurodegeneration	The progressive loss of structure or function of neurons, including the death of neurons, leading to diseases like Creutzfeldt-Jakob disease.
Protein Misfolding	The process where a protein does not fold into its correct three-dimensional shape, which for prions, allows it to induce misfolding in normal proteins.