Final answer:
Ethanol concentration in the CNS rises quickly due to its rapid absorption into the blood and enzymatic activity in the liver.
Step-by-step explanation:
In the central nervous system (CNS), the high speed of the rise of ethanol concentration can be explained by its quick absorption into the blood. Once consumed, ethanol is rapidly absorbed into the blood and its concentration decreases at a constant rate until it reaches zero. The rate at which ethanol is formed in the body is determined by the amount of enzyme present in the liver, not by the amount of ethanol consumed. Therefore, the higher the enzyme activity, the faster the rise in ethanol concentration in the CNS.