ANATOMY

Detailed explanation-1: -O2 is consumed by the tissue to release energy and CO2 is released into the blood which makes it dark.

Detailed explanation-2: -RBCs contain hemoglobin (pronounced: HEE-muh-glow-bin), a protein that carries oxygen. Blood gets its bright red color when hemoglobin picks up oxygen in the lungs. As the blood travels through the body, the hemoglobin releases oxygen to the different body parts.

Detailed explanation-3: -The iron-containing complex protein known as haemoglobin is present in red blood cells (RBC). The haemoglobin contains red-colored compound heme, because of which the blood looks red in color. This heme compound helps in transporting oxygen in our blood.

Detailed explanation-4: -The blood that flows through the lungs into the heart is arterial blood. It has a bright red colour because it contains oxygen. While the blood which flows to the lungs is venous blood. It has a dark red colour because it contains carbon dioxide.

Detailed explanation-5: -The blood that travels back to the heart and lungs is dark red. It has picked up carbon dioxide from the body cells, and it has left most of its oxygen with the cells. We can think of the dark colored, carbon dioxide-rich blood as “used” blood. This is the blood that the heart pumps into the lungs.