How do you know plants contain energy rich substances

Plants use energy from the sun to produce foods which are very rich in energy. The food are mostly in form of sugar and they can be converted to starch for storage. 
When plants needs energy, they undergo a process called cellular respiration in which the food that is stored is combine with oxygen in order to release energy for plant use. This show that the compounds that are produced during photosynthesis contain energy.

I'm sorry to hear that. i will try to answer your other questions if it is within my ability. : )answers: my favourite colour is black.my favourite food is pasta.my favourite school subject is english, but i do also like lunch time.my least favourite subject is history as well as geography. i have currently garnered a quite equal hatred for both of the subjects.what about you? well, you for the points. : )