Microscopy

OCR

GCSE

Microscopy facilitates the investigation of cell structure through the magnification of specimens using light or electron beams. Candidates must differentiate between magnification and resolution, understanding that the shorter wavelength of electron beams allows for higher resolution and the visualization of ultrastructure. Proficiency in applying the magnification formula (Image size = Actual size × Magnification) and converting units (millimetres, micrometres, nanometres) is critical for accurate biological measurement.

Objectives

Exam Tips

Pitfalls

Key Terms

Mark Points

What You Need to Demonstrate

Key skills and knowledge for this topic

Award 1 mark for correct substitution into the formula: Magnification = Image size / Actual size
Award 1 mark for converting units correctly (e.g., millimetres to micrometres) before calculation
Credit responses that define resolution as the ability to distinguish between two separate points
Award 1 mark for stating that electron microscopes have higher resolution and magnification than light microscopes
For slide preparation: Award 1 mark for lowering the coverslip at an angle using a mounted needle to prevent air bubbles

Example Examiner Feedback

Real feedback patterns examiners use when marking

"You correctly identified the formula, but check your unit conversions—did you convert mm to µm?"
"Good description of the electron microscope, but you must use the term 'resolution' rather than just 'detail'"
"When describing the slide prep, explain *why* you lower the coverslip at an angle (to avoid air bubbles)"
"Your calculation is correct, but remember to express very large or small numbers in standard form for Higher Tier credit"

Marking Points

Key points examiners look for in your answers

Award 1 mark for correct substitution into the formula: Magnification = Image size / Actual size
Award 1 mark for converting units correctly (e.g., millimetres to micrometres) before calculation
Credit responses that define resolution as the ability to distinguish between two separate points
Award 1 mark for stating that electron microscopes have higher resolution and magnification than light microscopes
For slide preparation: Award 1 mark for lowering the coverslip at an angle using a mounted needle to prevent air bubbles

Examiner Tips

Expert advice for maximising your marks

💡Always measure the image size in millimetres first, then convert to micrometres (x1000) before using the formula
💡When asked to compare microscopes, explicitly state that electron microscopes have *both* higher magnification and higher resolution
💡Show full working for calculations; OCR often awards 'allow' marks for correct methods even if the final answer is wrong due to a slip

Common Mistakes

Pitfalls to avoid in your exam answers

Dividing Actual size by Image size instead of Image by Actual (M = I/A)
Failing to convert measurements to the same unit (e.g., dividing mm by µm directly) resulting in answers off by a factor of 1000
Stating that electron microscopes are simply 'better' without specifying higher resolution or magnification
Confusing the purpose of staining (to provide contrast/identify organelles) with preserving the specimen

Key Terminology

Essential terms to know

Magnification versus Resolution

Light Microscopy versus Electron Microscopy (TEM and SEM)

Quantitative Microscopy (Formula application and Unit Conversion)

Specimen Preparation and Staining Techniques

Likely Command Words

How questions on this topic are typically asked

Calculate

Compare

Describe

Explain

Estimate

Practical Links

Related required practicals

•{"code":"PAG 1","title":"Microscopy","relevance":"Preparation of slides (onion cells/cheek cells) and use of light microscope"}

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