Explain how the human circulatory system is adapted to: 1. supply oxygen to the tissues 2. remove waste products from tissues.

The human circulatory system has dual / double system which means that it has higher blood pressure and a greater flow of blood to the tissues. The heart is made of specialised (cardiac) muscle cells which have long protein filaments that can slide past each other to shorten the cell to bring about contraction for pumping blood. The heart pumps blood to lungs in pulmonary artery so that oxygen can diffuse into blood from air in alveoli. Blood returns to heart via pulmonary vein where muscles pump blood to the body via aorta. Oxygen carried by specialised cells / RBCs which contain haemoglobin to bind oxygen and have no nucleus so there is more space available to carry oxygen. Arteries carry oxygenated blood to tissues where capillaries deliver oxygen to cells for respiration and energy release. They have thin walls allow for easy diffusion to cells. Other points to consider:-large surface area of capillaries to maximise exchange-waste products removed eg CO2 diffuse from cells into the blood plasma-blood goes back to the heart in veins which have valves to prevent backflow-cardiac output can vary according to demand / is affected by adrenaline