Heart valves open and close because of

  1. hormones
  2. differences in blood pressure on either side
  3. muscles attached to valves
  4. nerve impulses
Answer

B) differences in blood pressure on either side

Valves respond passively to pressure. AS & A Level Biology · Topic 8 Transport in Mammals · 8.3 The heart

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