8. Transport in mammals
A section of Biology, 9700
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Describe the roles of the sinoatrial node (SAN) and the atrioventricular node (AVN) in the initiation and control of the cardiac cycle. The Purkyne fibres pass down the septum and extend to the cardiac muscle at the base of the heart. Explain why it is important that the Purkyne fibres extend to the base of the heart. The activity of the SAN is controlled by the nervous system. Noradrenaline is released by nerve cells in the SAN. shows the role of noradrenaline in causing calcium ions (Ca2+) to enter a cell in the SAN. noradrenaline phospholipid bilayer ATP cAMP (second messenger) inactive enzyme active enzyme active enzyme opens channel protein Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ small gap cell surface membrane of SAN cell With reference to , outline the process of cell signalling.
9700_w18_qp_23
THEORY
2018
Paper 2, Variant 3
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The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries. The mammalian heart consists of four chambers. Explain why the ventricles have thicker walls than the atria. Complete Table 6.1 to identify the structure in the heart responsible for each function listed. Table 6.1 function structure in the heart initiates the heartbeat delays the wave of depolarisation between the atria and the ventricles transmits the wave of depolarisation through muscles of the ventricle closes when the left ventricle contracts
9700_w23_qp_23
THEORY
2023
Paper 2, Variant 3
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