Lesson Plan

• Calculate total magnification for light and electron microscopes using the appropriate formula.
• Determine the actual size of a specimen from hand‑drawn sketches, photomicrographs, SEM and TEM images.
• Apply scale‑bar conversions to obtain real dimensions in µm or nm.
• Interpret calculated sizes to answer biology‑based questions about cell structures.

• Projector or interactive whiteboard
• Printed micrographs (hand‑drawn, digital, SEM, TEM)
• Rulers and transparent grids
• Computer with image‑analysis software (e.g., ImageJ)
• Scale‑bar reference sheets
• Worksheet with practice problems
• Scientific calculators

Start with a quick poll asking students how they would estimate the size of a cell shown in a textbook image. Review that magnification equals objective power multiplied by eyepiece power and that this relationship underpins all size calculations. Explain that by the end of the lesson they will be able to convert any measured image dimension into a real‑world specimen size and verify it against known biological values.

1. Do‑now (5'): Students answer a short question on the magnification formula and submit their response.
2. Mini‑lecture (10'): Review total magnification, introduce scale‑bar concepts for digital and electron images.
3. Guided practice – Hand‑drawn sketch (10'): Measure a feature with a ruler, identify magnification, calculate actual size, discuss results.
4. Guided practice – Photomicrograph (10'): Open an image in ImageJ, measure pixels, compute conversion factor, calculate specimen size.
5. Guided practice – SEM/TEM (10'): Locate scale bar, measure in pixels, derive k, calculate real dimensions for a sample structure.
6. Independent worksheet (10'): Mixed problems covering all media types; teacher circulates for support.
7. Exit ticket (5'): Write one real‑world example where accurate size calculation is essential.

Summarise the step‑by‑step workflow from measuring an image to obtaining the actual specimen size and highlight common pitfalls. Collect the exit tickets to gauge understanding and assign a short homework task: students must find a published micrograph, record its scale bar, and calculate the size of a chosen structure.