The semilunar valves close when

  1. pressure in the arteries exceeds pressure in the ventricles
  2. the AVN fires
  3. atrial pressure rises
  4. ventricles contract
Answer

A) pressure in the arteries exceeds pressure in the ventricles

Backflow is prevented in diastole. AS & A Level Biology · Topic 8 Transport in Mammals · 8.3 The heart

Biology MCQ · More A Level Biology: Transport in mammals MCQs · Practise