Equations Needed For GCSE Biology

1. Magnification:

• Magnification = Image size / actual size
  
  • You'll need to be able to measure the image size using a ruler, in mm, and convert this measurement to μm.
  • You’ll need to be able to rearrange this equation. For example, to find the actual size you would use: Image size / magnification.

2. Total Magnification:

• Total Magnification = Eyepiece lens magnification x objective lens magnification.
  
  • This equation helps calculate the total magnification when using a microscope with these two lenses.

3. Rates of Reaction:

• Rate of reaction = Change in value / Change in time.
  
  • This formula is used to quantify how quickly a reaction is occurring, which can be applied to various biological processes, such as enzyme activity or decomposition. 
  • When finding rate from a graph use: change in y / change in x.

4. Body Mass Index (BMI):

• BMI = Weight / Height²
  
  • Weight must be in kg and height must be in metres.
  • BMI is a measure that helps assess whether someone's weight is healthy for their height.

5. Aerobic Respiration:

• Word equation: Glucose + Oxygen 🡪 Carbon dioxide + Water
• Chemical equation: C₆H₁₂O₆ + 6O₂ 🡪 6CO₂ + 6H₂O

6. Anaerobic Respiration:

• Word equation (animals): Glucose 🡪 Lactic acid
• Word equation (plants and fungi): Glucose 🡪 Ethanol + Carbon dioxide

7. Photosynthesis:

• Word equation: Carbon dioxide + Water 🡪 Glucose + Oxygen (requiring light energy)
• Chemical equation: 6CO₂ + 6H₂O 🡪 C₆H₁₂O₆ + 6O₂

8. Higher tier only

The Inverse Square Law:

• Light intensity  ∝  1 / d² 

Where:

• d = distance from the light source (in cm or m)
• Light intensity and distance are inversely related – when distance doubles, light intensity drops to a quarter.

Practice Questions