Explain how the properties of water make it suitable as the main component of blood.
Finish Fig. 2.1 by naming P and Q. Put your answers on Fig. 2.1.
Fig. 2.1 shows the circulation in a mammal.
Describe the functions of P and Q.
Explain why the mammalian circulation is described as a closed, double circulation.
Fig. 2.2 is a transmission electron micrograph showing a cross-section of an arteriole. Blood passes from muscular arteries through arterioles into capillary networks. The lining of the arteriole is folded because the arteriole has constricted. This narrowing reduces the blood pressure from $12.7\,\text{kPa}$ in the muscular artery to $2.7\,\text{kPa}$ at the end of the arteriole.
Explain why it is important that the pressure of blood decreases as it passes through arterioles.
Compare the structure of a muscular artery with the structure of the arteriole shown in Fig. 2.2.