Biology 9700 · AS & A Level · Movement into and out of cells

Movement into and out of cells — practice question

The diagram shows the electrical activity in cardiac muscle during one heartbeat. What is occurring at each of the labelled stages in the cardiac cycle?

  • AO: atria contract; P: atrio-ventricular valve opens; QRS: atria relax; T: ventricles contract
  • BO: impulse leaves AVN; P: ventricles contract; QRS: atria relax; T: atrio-ventricular valve closes
  • CO: impulse leaves SAN; P: atria contract; QRS: ventricles contract; T: ventricles relax
  • DO: ventricles relax; P: atria contract; QRS: atrio-ventricular valve closes; T: ventricles relax

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