Describe how the blood arriving at the arterial end of the capillary network differs from the tissue fluid around the body cells.
Not every part of the tissue fluid returns to the blood capillaries to re-enter the bloodstream. Some of the tissue fluid flows into blind-ended vessels, such as vessel $X$ shown in Fig. 3.1. Name the fluid that is formed in vessel $X$.
Explain why hormone $S$, shown in Fig. 3.2, can enter the cytoplasm of the target cell without using a transport protein.
The target cell is able to respond to other cell signalling molecules as well as hormone $S$. It has receptors in the cell surface membrane, in the cytoplasm and in the nucleus. Explain why hormone $S$ binds only with receptor $R$ in the cytoplasm and not with the other receptors shown in Fig. 3.2.
Name the structure through which the hormone-receptor complex enters the nucleus.
State the process taking place at $B$ and at $C$. $B$: $C$:
State the name of structure $G$.
Cell signalling by hormone $S$ leads to the formation of a functioning globular protein molecule made of three identical polypeptide chains. Once these polypeptides have been synthesised, changes must take place to produce the functioning globular protein molecule. Outline the changes that need to occur to form the functioning globular protein molecule.