This tortoise is eating cactus on a sunny day. Is carbon moving into the air, moving out of the air, or both?

Carbon is moving into the air, and out of the air at the same time. This is because as the tortoise  feeds, and inhales O2, the food(cactus-cellulose) is oxidized  (glucose + oxygen) during cellular respiration with CO2+H20(waste products)+ATPs( as the main product). The CO2 in the equation is the form by which carbon is liberated into the air.

On a sunny day the Cactus, takes in CO2(with Carbon contents) through the stomata, for photosynthesis. This is the form Carbon enters the cactus at the same time.

Thus Carbon leaves and enter at the same time.

Explanation:

allowed for the prediction of the properties of missing elements.