Micrographs, Magnification & Scale – Exam Quick Notes

Microscopy Basics

• Electron microscopes provide higher magnification than light microscopes.
• Micrographs = photos taken with an electron microscope for studying cell organelles.
• Main tasks with micrographs:
  • Determine actual size of structures.
  • Produce accurate biological drawings.
• Common units:
  • $1\ mm = 1000\ \mu m$
  • $1\ mm = 10^6\ nm$

Calculating Actual Size – Magnification Given

• Magnification is shown as $\times n$ (e.g.
  $4500\times,\ 1000\times$).
• Steps:
  1. Measure structure in the image (mm).
  2. Actual size $= \frac{image\ size}{magnification}$ (in mm).
  3. Convert to $\mu m$ if required: $mm \times 1000 = \mu m$.
• Example: $\frac{89\ mm}{3300} = 0.02697\ mm = 26.97\ \mu m$.

Calculating Actual Size – Using a Scale Line

• A scale line gives image : real-size ratio.
• Procedure:
  1. Measure scale line length (mm) – represents stated real length (e.g. $1\ \mu m$).
  2. Measure the structure (mm).
  3. Number of scale lines across structure $= \frac{structure\ length}{scale\ line\ length}$.
  4. Actual size $= (\text{number of scale lines}) \times (\text{real length represented})$.
• Example: $\frac{65\ mm}{18\ mm}=3.61$ → actual diameter $=3.61\ \mu m$.
• Ratio form: $\frac{1\ \mu m}{18\ mm}=\frac{real\ size}{65\ mm}$.

Determining Magnification from a Scale Line

• Given: scale line represents a real length (e.g. $200\ nm$).
• Steps:
  1. Measure scale line in mm.
  2. Convert this measurement to nm: $mm \times 10^6 = nm$.
  3. Magnification $= \frac{scale\ line\ length\ (nm)}{real\ length\ represented\ (nm)}$.
• Result gives the $\times$ value of magnification.

Quick Conversion Reminders

• $\mu m \rightarrow mm: \div 1000$.
• $nm \rightarrow mm: \div 10^6$.
• Keep units consistent throughout all calculations.