A vein in the leg has damaged valves. A surrounding muscle still squeezes the vein normally. Why can this reduce the net return of blood towards the heart?
Blood can flow both ways, so less moves towards the heart.
Blood can flow one way, so more moves towards the heart.
Blood pressure becomes zero, so the muscle cannot squeeze the vein.
Blood pressure becomes arterial, so the muscle cannot squeeze the vein.
42 exam-style questions on Edexcel GCSE Biology 8.2 Blood and circulation, covering 8.2.1 Structure and function of the blood, 8.2.2 Structure of blood vessels, 8.2.3 Structure of the heart and circulatory system, and 8.2.4 Cardiac output. Each one has a worked solution and a mark scheme showing where the marks go.