A chemical reaction will occur not only at one temperature; however, the turnover is higher in a warmer ambient. To provide an example, plants are growing much faster the warmer it gets during spring.
In the human body the temperature is at 37°C, but lower in the extremities, at the skin. Even more extremes can be observed in extraordinary situations like heat (fever, sauna) or when freezing (hypothermia). Under each of these situations the body must function and likewise the reactions need to work.
A typical biological, enzymatic reaction (glycolysis or citrate cycle) can take place from below 0°C (salts keep the water melted) to 45°C or much higher (thermophil bacteria: higher than 100°C, high water preasure keeps the boiling temperature even higher).