There could be many answers to this question, but a possible one is embryo!!
"The word cycle tells you that the chemical reactions of the Calvin cycle go from one to another with a beginning and an end / with no beginning or end. The overall process of cellular respiration converts sugar into ATP using oxygen. MAIN IDEA: Cellular respiration makes ATP by breaking down sugars."
of course answer is thymine
ATP is the chemical substance that is used to power the cellular activities
Lungs have a pulmonary circulation
