A-LevelBiologyTransport in mammals9700/23 · Oct/Nov 2018 · Q410 Marks

Describe the roles of the sinoatrial node (SAN) and the atrioventricular node (AVN) in the initiation and control of the cardiac cycle.

(a)Describe the roles of the sinoatrial node (SAN) and the atrioventricular node (AVN) in the initiation and control of the cardiac cycle.[4]
(b)The Purkyne fibres pass down the septum and extend to the cardiac muscle at the base (apex) of the heart. Explain why it is important that the Purkyne fibres extend to the base of the heart.[2]
(c)The activity of the SAN is controlled by the nervous system. Noradrenaline is released by nerve cells in the SAN. Fig. 4.1 shows the role of noradrenaline in causing calcium ions (Ca2+) to enter a cell in the SAN. With reference to Fig. 4.1, outline the process of cell signalling. [Figure 4.1][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 (Oct/Nov 2018). The mark or mark type is shown in brackets.

[(a) any four from]
I signals R nerve impulse first time
SAN
[1] acts as a pacemaker / initiates heart beat / initiates cardiac cycle ; A regulates heartbeat A described, e.g. as rhythm / emits impulses at regular intervals
[2] releases / AW, waves of excitation / (electrical) impulses ; A ref. to, action potentials / depolarisation R nerve impulses
[3] spread across / AW, atria / atrial walls or leads to atrial, systole / contraction(s);
AVN
[4] allows a (short) delay / ~0.1 s;
[5] passes the impulse / wave of excitation, to the Purkyne fibres / down the septum ; A Bundle of His R nerve impulse
[6] detail; e.g. so atria contract before ventricles allows ventricles to fill / allow atria to empty completely so atria have, emptied / contracted, before ventricular contraction begins so atria and ventricles don't contract at the same time
[(b) any two from]
contraction / ventricular systole, begins at the base of the ventricles ;
both ventricles contract at the same time;
blood is forced, upwards / into arteries / through (named) semi-lunar valves ; A pushed
idea that so ventricles, empty / pump out most of the blood ;
AVP; e.g. so impulses / waves of excitation, travel upwards from the base
[(c) any four from]
[1] noradrenaline is, signalling, molecule / compound; A noradrenaline is the signal I noradrenaline is a (neuro)transmitter
[2] SAN cell is the target cell;
[3] noradrenaline / signalling molecule, binds to (cell surface) receptors (of target cell) ; A 'fits' R 'receptor cells'
[4] receptors are specific to noradrenaline; A ref. to complementary (shapes)
[5] ref. to formation of cAMP / second messenger or activating enzyme ;
[6] response is the opening of channel proteins (so calcium ions enter) ;