Endosymbiosis Model
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About This MicroSim
This step-through visualization walks through the endosymbiotic theory in six stages: ancestral cells, engulfment of an aerobic bacterium, its transformation into a mitochondrion, the five key pieces of molecular evidence, a second engulfment of a cyanobacterium becoming a chloroplast, and the modern eukaryotic cell with both organelles. An "Evidence" toggle shows the supporting evidence at each stage, and a "Double Membrane" toggle highlights the origin of the double membrane (inner from the endosymbiont, outer from the host's vesicle).
How to Use
- Click "Next" to advance through the six stages of endosymbiosis.
- Click "Evidence" to display an evidence card showing the molecular and structural evidence relevant to the current stage.
- Click "Double Membrane" to highlight the two membranes and their origins (inner = bacterium, outer = host vesicle).
- Read the description panel at each step for detailed explanations.
- Use "Previous" to revisit earlier stages.
Lesson Plan
Grade Level
9-12 (college placement Biology)
Duration
10-15 minutes
Prerequisites
- Understanding of prokaryotic vs. eukaryotic cell structure
- Knowledge of organelle functions (mitochondria, chloroplasts)
- Familiarity with cellular respiration and photosynthesis
Activities
- Exploration (5 min): Step through all 6 stages with both "Evidence" and "Double Membrane" toggled on. At each stage, identify which organisms are present and what is happening.
- Guided Practice (5 min): List the 5 pieces of evidence for endosymbiosis from memory. Then toggle "Evidence" at Step 4 to check your list. Which piece of evidence do you find most convincing and why?
- Assessment (5 min): Explain why chloroplasts are only found in plants and algae (not all eukaryotes), but mitochondria are found in nearly all eukaryotes. Use the timeline shown in Step 6 to support your answer.
Assessment
- Can students list at least 4 of the 5 key pieces of evidence for endosymbiosis?
- Can students explain the origin of the double membrane?
- Can students explain why the second engulfment (chloroplasts) only occurred in one lineage?
- Can students describe the relationship between endosymbiotic gene transfer and organelle dependence on the host?