Use a model’s scale honestly

Supplied materials

• All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
• Paper or a browser document for a labeled drawing, table or explanation.
• Worked problem inputs: Drawing A is 20 mm long at 100× magnification; drawing B is 30 mm at 300×. Compare actual represented lengths.
• Assessment case 1: A specimen is drawn 40 mm long at 200 × magnification. What inference follows? Which inference or prediction is best supported?
• Assessment case 2: Which scientific label fits the specifically described step or feature? Supplied case: Width of a printed drawing.
• Assessment case 3: Which scientific label fits the specifically described step or feature? Supplied case: Drawing enlarged one hundredfold.
• Assessment case 4: Which scientific label fits the specifically described step or feature? Supplied case: Line labeled ten micrometers.
• Assessment case 5: Which scientific label fits the specifically described step or feature? Supplied case: Real cell length rather than printed length.
• Assessment case 6: Two drawings share a 10 μm labeled reference bar, printed at different lengths. What comparison is justified? Which inference or prediction is best supported?

Learn the idea

Microscope images and drawings use magnification. A larger drawing need not mean a larger actual cell. Compare scale bars before comparing image sizes; the supplied cases are schematic.

Actual size means physical size of the specimen. Image size means size of its representation. Magnification means image-to-actual size ratio. Scale bar means reference showing actual represented length.

For the supplied mechanism problem, Drawing A is 20 mm long at 100× magnification; drawing B is 30 mm at 300×. Compare actual represented lengths. A represents 20/100=0.2 mm; B represents 30/300=0.1 mm. Although B’s drawing is larger, A’s represented cell is twice as long.

1. Read the supplied problem and mark the structures, processes or quantities named: Drawing A is 20 mm long at 100× magnification; drawing B is 30 mm at 300×. Compare actual represented lengths.
2. Draw the relevant boundary, pathway or comparison and label it using the scientific ideas above.
3. Write a causal explanation or calculation, showing how each observation supports the result.
4. Compare your reasoning with the worked solution; name a condition that would change or limit the inference.

Check your reasoning

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Take it further

New scale case: image A is 12 mm at 60× and B is 15 mm at 150×. Expected: actual represented lengths are 0.2 mm and 0.1 mm; A represents the larger cell although B is printed larger.

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