Outline the mechanisms involved in the control of heartbeat.

Explain how the direction of blood flow in the heart is controlled.

myogenic contraction / muscles contract without stimulus from a nerve;
pacemaker/SA node initiates each heart beat/stimulates atria to contract;
nerves carry impulses from the brain to speed up and slow down the heart;
medulla (of the brain) monitors blood pressure;
epinephrine/adrenaline increases rate/strength of contractions;

valves open/close due to blood pressure differences;
valves prevent backflow/only allow unidirectional flow;
atrioventricular valves between ventricles and atria;
semilunar valves between arteries and ventricles;
Accept mitral/bicuspid and tricuspid in place of atrioventricular.
Accept aortic and pulmonary in place of semilunar valves.

This question could perhaps have been worded more clearly as many candidates described the electrical stimulation of contraction of the atria and ventricles of the heart. What was required was a description of how the rate of beating of the heart is controlled, as in assessment statement 6.2.4, with the teacher notes for that statement giving all the points that were expected.

This was answered more successfully, with many candidates explaining that heart valves prevent backflow and giving details of specific valves. Few candidates explained that pressure differences on the two sides of a heart valve cause opening and closing, but it was still possible to score two marks without including this.