An effective gas exchange system helps to keep the diffusion gradient steep, gives a large total surface area and has a short diffusion distance. Which feature of the human gas exchange system helps to keep the diffusion gradient steep?
- AA large number of alveoli are present in each lung.
- BAlveoli walls contain elastic fibres allowing expansion.
- CThe air brought into the alveoli by ventilation is high in oxygen.
- DThe endothelium of the capillary wall is made of flattened cells.