Answer:
The center organ is the heart. Above the heart, lungs are present while below the heart is body of organism. The artery which takes blood from the heart to the lungs is called pulmonary artery. This blood contains a lot of carbondioxide gas while the blood which comes to the heart from the lungs has a lot of oxygen and the blood vessel is called pulmonary vein.
The blood vessel which carries blood from body to heart is called vein and this blood has a lot of carbondioxide while the blood vessel which carries blood from the heart to the body is called arteries and this blood has a lot of oxygen.