Start a short session
Check your answer after each question. Use a calculator where needed.
Cell sizes · osmosis · measurements
Units and standard form
Practise mm, μm and nm conversions, standard form and percentage changes using biological measurements. Check each answer and see the working.
Method and worked examples ↓Learn the method
How to approach these questions
- 1 m = 1,000 mm; 1 mm = 1,000 μm; 1 μm = 1,000 nm.
- Going to a smaller unit increases the numerical value. Going to a larger unit decreases it.
- For percentage change, use (final − initial) ÷ initial × 100. Keep the sign.
- A negative percentage change means a decrease. It is not the percentage of the original amount remaining.
Worked examples
Convert 0.006 mm into μm and write the same length in metres in standard form.
0.006 × 1,000 = 6 μm. In metres, 6 μm = 6 × 10⁻⁶ m.
A potato cylinder changes from 2.50 g to 2.20 g. Calculate its percentage change in mass.
(2.20 − 2.50) ÷ 2.50 × 100 = −12%. The negative sign shows that mass decreased.
Keep practising
Topic map and study list · Practical data guides · Active recall decks
Course resources
AQA A-level Biology · OCR A A-level Biology · Textbook answers
Skill coverage follows the common A-level science subject content. Check your board’s current requirements: AQA 7402 and OCR A H420.