While Darwin is running, his heart beats faster. This causes more blood to flow from his lungs to his muscle cells. Which of these would Darwin's muscle cells absorb from the blood?

The higher you go up the less oxygen there is 

I’m not exactly sure what your trying to ask, but if it’s how an organelle is similar to a body system or a part a nucleus is like a in function. but i don’t fully understand what you’re trying to ask