Respiration

• Cellular respiration: Oxidation of organic macromolecules inside cells to release energy (thermal or chemical as ATP) in a series of linked, enzyme-catalysed reactions
• Photoautotrophs use light/thermal energy to synthesise complex organic molecules from simple inorganic molecules and ions; they are producers in many food chains: plants, some protoctists and some bacteria
• Heterotrophs are consumers/decomposers in food chains: animals, fungi, and most bacteria obtain their complex organic molecules and energy by feeding on photoautotrophs or other heterotrophs
• All organisms must respire to transfer potential chemical energy of carbohydrates, lipids and proteins to chemical energy (ATP) and thermal energy, which is important to maintain cell temperature (for enzyme-controlled reactions)