(a) Describe the structure of the mammalian heart, naming its chambers, the valves and the main blood vessels attached to it. (7 marks) (b) Explain what is meant by double circulation and state two advantages it gives mammals. (4 marks) (c) State the functions of the following components of blood: (i) red blood cells (ii) white blood cells (iii) platelets (iv) plasma. (4 marks)