9.4) Blood Red blood cells: they contain haemoglobin - a red protein that combines with oxygen they have no nucleus so they can contain more haemoglobin they are small and flexible so that they can fit through narrow blood vessels they have a biconcave shape...
9.1) Transport in animals The blood, pumped by the heart, travels all around the body in blood vessels. It leaves the heart in arteries and returns in veins. Valves, present in the heart and veins, ensure a one-way flow for the blood, as blood enters an organ,...
9.2) Heart The heart pumps blood through the circulatory system to all the major organs of the body. Valves: In general, blood flows into the heart from a vein, goes into an atrium, then a ventricle, and out through an artery. The heart contains valves...
9.3) Blood and lymphatic vessels Arterioles, shunt vessels and venules: The small arteries and arterioles have proportionately less elastic tissue and more muscle fibres than the great arteries. When the muscle fibres of the arterioles contract, they make the vessels...