the circulatory system 2.2.2

• the circulatory system is a type of transport system made up of the heart, blood and vessels
• a transport system is a way of moving material round an organism in bulk
• large multicellular animals need a transport system as most of their cells are far from the outside environment and they also have a small surface area to volume ration,

  therefore it would take too long for oxygen to diffuse into cells and waste products to be removed by diffusion,
• in a single circulatory system, blood passes through the heart once for every complete circuit
• in a double circulatory system, blood passes through the heart twice for every complete circuit
• fish have single circulatory systems
• animals and birds have double circulatory systems
• the systemic circuit carries oxygenated blood from the heart to the rest of the body and then the deoxygenated blood back to the heart to be pumped out to the lungs again
• the pulmonary circuit carries deoxygenated blood from the heart to the lungs and then the oxygenated blood back to the heart
• the double circulatory system makes our circulatory systems more efficient as blood can be sent off to different parts of the body at high pressure and oxygenated and deoxygenated blood do not mix together
• active animals would run out of energy with a single circulatory system because our metabolism is too high and all the reactions around the body would begin to fail