Biologists used the world's largest single-celled organism, an aquatic alga called Caulerpa taxifolia, to study the nature of structure and form in plants. It is a single cell that can grow to a length of six to twelve inches.
Because they are the same chemical reaction but reversed. Cellular respiration takes glucose (from nutrient/food) and oxygen (from atmosphere) in order to make CO2 (think about exhaling) and H20 (water).
(I don't remember this clearly so it may be wrong, i'll look into it and come back!)
Answer:
because people where not alive yet oontill cenoznic era
Explanation: