Lesson Plan

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Lesson Plan
Grade: Date: 25/02/2026
Subject: Biology
Lesson Topic: Explain that groups of organisms which share a more recent ancestor (are more closely related) have base sequences in DNA that are more similar than those that share only a distant ancestor.
Learning Objective/s:
  • Describe how DNA sequence similarity reflects evolutionary relationships.
  • Explain why organisms with a recent common ancestor have more similar DNA.
  • Interpret a simple phylogenetic tree to infer relative relatedness.
  • Apply the concept of a molecular clock to estimate divergence times.
Materials Needed:
  • Projector and screen
  • PowerPoint slides with DNA similarity data
  • Printed handout of the DNA similarity table
  • Blank phylogenetic tree worksheets
  • Markers / coloured pencils
  • Exit‑ticket slips
 Introduction:
Begin with a quick poll: “If two species share 98% of their DNA, are they more closely related than species sharing 70%?” Use this to activate prior knowledge about DNA and evolution. State the success criteria: students will be able to explain the link between recent ancestry and DNA similarity and construct a basic phylogenetic tree.
Lesson Structure:
  1. Do‑now (5'): Students complete a short worksheet comparing DNA percentages and predict relatedness (formative check).
  2. Mini‑lecture (10'): Explain the molecular clock, DNA base composition, and why recent ancestors yield higher similarity (slides).
  3. Group activity (15'): Using the handout table, groups draw a simple rooted phylogenetic tree for humans, chimpanzees, gorillas, and orangutans.
  4. Class discussion (10'): Groups present trees; teacher highlights correct branching and common misconceptions.
  5. Guided practice (10'): Answer three questions on how DNA data updates classification systems.
  6. Exit ticket (5'): Write one sentence summarising why DNA similarity is valuable for taxonomy.
Conclusion:
Recap the key idea that DNA similarity mirrors evolutionary closeness and underpins modern classification. Collect exit tickets to gauge understanding and assign a brief homework: research an example of a species re‑classified due to new DNA evidence.