In which form do plants store energy?

Celluose. That's the "food product" of photosynthesis.

Spores are a method of reproduction, hormones are chemicals that cause changes or maintain something within an organism (i. e. estrogen is a hormone). Carbon dioxide is the gas that is necessary for photosynthesis, processed into oxygen. So CO2 comes in and goes out just as quickly.

The form of which plants store energy is cellulose.