The figures given below show diagrammatic cross sections of three kinds of blood vessels.

(a) Identify the blood vessels A, B and C.

(b) Name the parts labelled 1-4.

(c) Mention two structural differences between A and B.

(d) Name the kinds of blood that flow through A and through B respectively

(e) In which one of the above vessels referred to in (a) above does the exchange of gases actually take place?

(a) A is artery , B is vein & C is capillary.

Artery (thick muscular walls & narrow lumen)

Vein (thin muscular walls & wider lumen)

Capillary (very narrow tube )

(b) 1: Tunica externa (external layer connectives tissue)

2 : Lumen (cavity present in the blood vessel)

3 : Tunica media (middle layer smooth muscles & elastic fibres )

4 : Endothelium (single layer of squamous epithelium cells )

(c) Two structural difference between A & B are :

1. Artery has thick muscular walls while veins have thin & less muscular walls.

2. Artery have narrow lumen & elastic walls while veins have wider lumen & less elastic walls.

(d) Through A oxygenated blood flows while through B deoxygenated blood flows.

Oxygenated blood (blood carrying more oxygen & brought out from lungs)

De oxygenated blood (blood carrying less oxygen & more carbon dioxide)

(e) The exchange of gases actually takes place in (C) i.e. capillaries (as they are extremely thin and without any muscles).