During a dissection of a sheep heart, a student observes that the walls of the two upper chambers contain less cardiac muscle than the walls of the two lower chambers.
Which statement explains this difference?
The lower chambers generate pressure to send blood out of the heart, whereas the upper chambers move blood only into the chambers below.
The lower chambers contract less often than the upper chambers, so each contraction requires more muscle.
The lower chambers prevent blood mixing between the two sides, whereas the upper chambers allow blood to mix.
The lower chambers receive blood directly from veins, whereas the upper chambers receive it from the chambers below.
114 exam-style questions on OCR GCSE Biology 2.2 The challenges of size, covering 2.2.1 Exchange surfaces and surface area : volume ratio, 2.2.2 Substances transported in organisms, 2.2.3 The human circulatory system, 2.2.4 The heart and blood vessels, 2.2.5 Red blood cells and plasma, 2.2.6 Uptake of water and mineral ions by plants, 2.2.7 Transpiration and translocation, 2.2.8 Xylem and phloem, 2.2.9 Environmental factors and water uptake, and 2.2.10 Using a potometer. Each one has a worked solution and a mark scheme showing where the marks go.