The blood is red because it contains hemoglobin, a red protein. When the arteries transport it in its oxygen-rich form throughout the body, it turns bright red. When it rushes back to the heart through the veins, it’s still crimson, but darker.
The blood is red because it contains hemoglobin, a red protein. When the arteries transport it in its oxygen-rich form throughout the body, it turns bright red. When it rushes back to the heart through the veins, it’s still crimson, but darker.