How do fungi use carbon dioxide?

Plants use carbon dioxide in photosynthesis: Carbon dioxide + water ---> oxygen + glucose 6CO2 + 6H2O ---> C6H12O6 + 6O2 Animals don't photosynthesise. Answer: We use carbon dioxide to control the pH of our blood. If the level gets too low we tend to pass out. This can be caused by hyperventilation or by breathing pure oxygen. Low blood CO2 levels increase blood pH (it becomes more alkaline), this constricts the blood vessels which supply the brain, and inhibits the transport of electrolytes in the nervous system. The body sees this as a bad thing