Final answer:
Oxygen reaches the cells from blood through the process of diffusion from capillaries into the tissues, driven by a concentration gradient with carbon dioxide diffusing in the opposite direction.
Step-by-step explanation:
Oxygen-rich blood is pumped from the heart into the aorta, then to smaller arteries, and eventually reaches the capillaries. As the oxygen concentration within the blood is higher than in the tissue, oxygen diffuses from the capillaries into the cells of the tissue. This diffusion is driven by the concentration gradient, according to the peripheral gas exchange process. At the same time, carbon dioxide, which is more concentrated in the tissue cells due to cellular respiration, diffuses from the cells back into the blood to be carried away for exhalation.
The heart's dual-loop system ensures that deoxygenated blood is directed to the lungs to pick up oxygen and release carbon dioxide, while oxygenated blood is pumped through systemic circulation to deliver oxygen to the body. Red blood cells function as carriers of oxygen, which they pick up in the lungs from the alveoli and transport to the tissues of the body. The bright red color of oxygenated blood is due to the high oxygen content.