Using Units (OCR AS Biology): Revision Note

Using Appropriate Units

• It essential that the correct scientific measurements are used when discussing biological experiments

• Ensure that the correct symbols are used in conjunction with the unit of measurement

  • E.g. m³ for cubic metres

Units of Measurement Table

• cm³ is the same as millilitre (ml)

• dm³ is the same as litre (l)

Significant Figures

• Significant figures must be used when dealing with quantitative data

• Significant figures are the digits in a number that are reliable and absolutely necessary to indicate the quantity of that number

• There are some important rules to remember for significant figures

  • All non-zero digits are significant

  • Zeros between non-zero digits are significant

    • 4107 (4.s.f.)

    • 29.009 (5.s.f)

  • Zeros that come before all non-zero digits are not significant

    • 0.00079 (2.s.f.)

    • 0.48 (2.s.f.)

  • Zeros after non-zero digits within a number without decimals are not significant

    • 57,000 (2.s.f)

    • 640 (2.s.f)

  • Zeros after non-zero digits within a number with decimals are significant

    • 689.0023 (7.s.f)

• When rounding to a certain number of significant figures:

  • Identify the significant figures within the number using the rules above

  • Count from the first significant figure to the specified number

  • Use the next number as the ‘rounder decider’

  • If the decider is 5 or greater, increase the previous value by 1