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| Front | Where does transcription occur |
| Back | Nucleus |
| Front | Fe2+ / Fe3+ |
| Back | Structural component of haemoglobin to allow transport of oxygen to respiring tissue |
| Front | H + and OH- ions |
| Back | Affect acidity of solutionsH+ used in respiration to provide energy to make ATPH+ used in photosynthesis to provide energy to make ATP |