Answer:
The first thing to look at would be type of symmetry the organism exhibits. If it is asymmetrical then it would be a sponge and the discovery could stop right there. If not, other characteristics need to be investigated.
Knowing the type of body cavity this organism has would be helpful.
It would also be beneficial to know what type of skeleton (endo or exo) this organism has and what its appendages look like.
Finally, the type of digestive tract and the presence or absence of a head would help to determine what this creature is.
Cellular respiration and photosynthesis both have water and carbon dioxide in their reactions.
The ATP is the adenosine triphosphate. The ATP molecule has the three phosphate molecules attached with the adenosine. The ADP is the adenosine diphosphate. It has two phosphate groups. The number of phosphate molecules is responsible for the amount of energy in bonds. Hence the ATP molecule has the three phosphate group hence it has more stored energy as compared to the ADP molecule which has two phosphate group.