The answer is lag. The number of bacterial cells doubles at a constant, exponential rate during log phase, while growth rate and death rate are the same during stationary phase. The fourth phase is the death phase, when the rate of cell death is faster than the population growth.
Answer:
The normal body temperature for humans is 37 degrees Celsius. Most of the enzymes of a human's bodywork best at this temperature. If an enzyme was discovered which works best at 39 degrees Celsius, then it means that the enzyme works at elevated temperatures for events which require slightly higher temperatures.
The enzyme will most probably work for overcoming fever or for reducing the temperature of the body after exercise.