In mathematical modelling and statistical modelling, there are dependent and independent variables. The models investigate how the former depend on the latter. The dependent variables represent the output or outcome whose variation is being studied. The independent variables represent inputs or causes, i.e. potential reasons for variation. I hope that helped, Im new to this app so im sorry if it didnt help
the first answer as blood needs to be oxygenated to be passes round the body then when its deoxgenated it will return to the heart to be pumped around the body again
