A-LevelBiologyTransport in mammals9700/21 · May/June 2019 · Q512 Marks

The mammalian circulatory system is described as a closed double circulation. Explain why it is called a closed and double circulation. closed double

(a)The mammalian circulatory system is described as a closed double circulation. Explain why it is called a closed and double circulation. closed double[2]
(b)(i)Fig. 5.1 shows a drawing of an external view of a mammalian heart. Two cross-sections were made of the heart: • section 1 was made across the line A–B. • section 2 was made across the line C–D. Drawings of the two sections were viewed from above as shown by the arrow on Fig. 5.1. Fig. 5.2 is a drawing of section A–B. Fig. 5.3 is a drawing of section C–D. Name structures 1, 2 and 3, as shown in Fig. 5.2. 1 2 3[3]
(b)(ii)Explain why the wall of chamber Y is thicker than the wall of chamber X, as shown in Fig. 5.3.[3]
(c)Explain how the contractions of the chambers of the heart are coordinated during one cardiac cycle.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.

closed
blood flows through, (blood) vessels;
A three of heart, arteries, veins, capillaries
double
blood flows through the heart twice in one complete circulation (of the body) / AW ;
A ref. to pulmonary and systemic circuits / to lungs and rest of body
pulmonary vein ;
semi-lunar/AW, valve ; A pulmonary valve R aortic valve
right, atrium / auricle ;
any three from:
1 left ventricle / chamber Y, pumps blood into, systemic circulation / described or right ventricle / chamber X pumps blood into, pulmonary circulation / described or distance travelled by blood in systemic circulation is greater than distance travelled by blood in pulmonary circulation / AW;
2 to overcome great(er) resistance to flow in systemic circulation ; ora
3 high (blood) pressure is required for blood to travel around the systemic circulation ;
4 high pressure requires more muscular force ; ora
5 pulmonary capillaries, rupture easily / damaged by high pressure ;
I more cardiac muscle
any four from:
1 impulse/wave of excitation / AW, passes from SAN to atria (muscles);
R nervous impulse / signal once only
2 atria both contract, together / at the same time;
A atrial systole if not contradicted by one contracting before the other
3 atria contract before ventricles;
4 fibrous / non-conducting, tissue prevents impulse travelling to ventricles ;
5 impulse delayed at AVN ;
6 AVN passes impulse to, bundle of His / Purkyne fibres ;
7 Purkyne fibres conduct impulses to muscle in wall of ventricles ;
8 ventricles contract together (if mp2 not awarded) ; A ventricular systole if not contradicted as for atria
9 ventricles contract from the bottom upwards ;