Answer:
1) The mint leaves were able to sustain the candle flame because of plants ability to produce oxygen.
2) Ingenhousz demonstrated how a plant recycles energy through processes. In the dark, the plant cannot sustain a flame because it is only releasing carbon dioxide due to the lack of sunlight. But in the light the plant can overcompensate for it's carbon dioxide release with photosynthesis and produce oxygen for the flame therefore demonstrating the interdependence of energy producing processing in a living organism.
Step-by-step explanation: