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Year 11 · 2017 syllabus · Module 1 pilot

Tools extend and limit observation — Apply worksheet

Original practice. Write explanations that distinguish observations, evidence and claims.

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Name: __________________________ Date: ______________

Measure a cell using an image scale

Measure a cell using an image scaleCell span: 120 pixels40 pixelsrepresents 20 µm
Synthetic cell-image schematic: an original outline for scale practice, not a microscope photograph or a biological specimen. The scale bar and boundary span are in the same image plane.
Text description
  • An elongated cell outline spans 120 image pixels horizontally. A separate scale bar spans 40 image pixels and represents 20 micrometres. Only the outer boundary is depicted; no internal structure or species is identified.

An elongated cell outline spans 120 image pixels horizontally. A separate scale bar spans 40 image pixels and represents 20 micrometres. Only the outer boundary is depicted; no internal structure or species is identified.

Synthetic image calibration
Image featureLength in image pixelsKnown actual length (µm)
Scale bar4020
Horizontal cell span120To calculate

Question 1

Use the synthetic cell image above: a 40-pixel bar represents 20 µm and the cell spans 120 pixels. Calculate its horizontal size, showing the scale conversion.

Question 2

Would a one-second logger confidently resolve a 0.05 s peak? Explain.

Question 3

Both the cell image and its scale bar are enlarged by a factor of two. Recalculate the cell size and explain why its blurred boundary does not become better resolved.

Teacher answer key — 3 questions

Model responses identify the essential ideas. Accept scientifically correct alternatives that address the question; wording need not match exactly.

  1. 20/40 = 0.5 µm per pixel; 120 × 0.5 = 60 µm. The estimate uses a shared image scale and defined horizontal endpoints, not the physical size of your screen.
  2. No. The peak can occur between samples or be smeared by sensor response; use a suitably faster tool and check response.
  3. 240/80 × 20 = 60 µm: the ratio is unchanged. Enlarging existing pixels does not add resolved detail. Boundary ambiguity can dominate measurement uncertainty, so do not claim the synthetic size is an exact empirical measurement.