Microorganisms in the human colon are more often being described as mutualistic with human hosts rather than commensalistic. Why has this change in the definition of a symbiotic relationship occurred

Explanation:

This is because both the bacteria and human benefit from the association. In mutualistic association both organisms benefits and non suffer loss. The microoganisms in the colon play vital role in further digesting carbohydrates to release gas and also in producing vitamins such as vitamin k and the microbes benefited by receiving accomodation and feed on left over food waste.

The answer that completes the blank is AN EXTRASYSTOLE AND EXTRA CONTRACTION OF THE VENTRICLES. The frequent stimulation of the heart of the frog happens when single shocks are frequently done in succession and this is when the doublet occurs.