Cell structures — OCR GCSE Biology
Test yourself on Cell structures with OCR GCSE practice questions.
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Cell structures explained
Estimations provide rapid, sensible approximations of cell dimensions and populations when exact measurements are impractical.
Read the full explanation
Under a light microscope, field of view diameter can be measured using a stage micrometer or clear graticule. By counting how many cells fit end-to-end across this diameter, the average length of a single cell is estimated by dividing field diameter by cell count. Estimations are also used to verify whether calculated answers are physiologically reasonable, rounding values to one or two significant figures. This prevents unrealistic claims, such as calculating a human cheek cell diameter as several centimeters.
Your focus
- Estimate cell lengths by dividing field of view diameter by cell count across the field.
- Explain when estimation is preferred over exact measurement in biological investigations.
- Use order-of-magnitude estimates to validate calculations.
Cell structures exam tips
Marking Points
- dividing the measured field of view diameter by the number of cells spanning it
- stating that estimations assess whether calculated dimensions are biologically realistic
- rounding approximate biological values appropriately to one or two significant figures
Examiner Tips
- 💡State the formula used: average cell size equals diameter of field of view divided by number of cells across diameter.
- 💡Use estimations to check your calculations; an answer of 20 mm for cell diameter is an immediate clue that unit conversion went wrong.
Common Mistakes
- dividing total cells visible in the entire circular field of view rather than cells spanning the diameter line
- giving an estimated value to excessive decimal places rather than appropriate significant figures