Answer:
Cellular Level, Tissue Level, Organ Level, System Level , Organism
Explanation:
Answer:
The oxygen enters the bloodstream from the alveoli, which are tiny sacs in the lungs where gas exchange takes place. The transfer of oxygen into the blood is through simple diffusion. While oxygen moves from the capillaries and into body cells, carbon dioxide moves from the cells into the capillaries and starts with high concentration but fades to low concentration.
Explanation:
C. Aorta
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