Unit 1 Defences against pathogens, the human immune system and vaccination Unit 2 Rate of reaction Unit 3 Aerobic and anaerobic cellular respiration Unit 4 Forces make things change Unit 5 Biomass transfer, food security and biodiversity Unit 6 Using Earth's resources Unit 9 Hormones and human reproduction Unit 10 Groups of the periodic table Unit 11 Coordination and control: maintaining a constant internal environment Unit 12 Electromagnetism Unit 14 Atmosphere and changing climate Unit 15 Medicines and new treatments for disease Unit 16 Electromagnetic waves Unit 17 Variation and natural selection at the genetic level Unit 19 Classification in modern biology