Coffee, cells and Nighty-night

How coffee (caffeine) actually works on the cellular level to keep you awake:

http://www.sfn.org/index.cfm?pagename=brainBriefings_adenosineAndSleep

"Scientists once believed that the peppy chemical caffeine induced its effects by blocking the same sedating mechanisms that tranquilizers like Valium enhanced. But in 1981, researchers found that caffeine's kick stemmed from its relationship to the chemical adenosine.

Normally, adenosine attaches to special receiving areas on cells, or receptors, and sets off distinct actions. Studies of rats revealed, however, that caffeine stonewalls these receptors, blocks adenosine from carrying out its job, and as a result induces alertness. This suggested that adenosine plays a role in sleep. Now increasing evidence is confirming that, indeed, adenosine is an important "fatigue factor.""

Adenosine is a broken-down piece of a bigger molecule abbreviated as ATP. ATP is what gives us energy. Apparently, adenosine accumulates as you are awake and active, attaches to your cells and cues sleepiness.

So it's like the cellular equivalent of dirt accumulating on your car suggesting strongly to you that you ought to run it through the car wash. Or of waste products accumulating in your bladder, signifying with more urgency each minute that you really ought to take a trip to the restroom.

A whole lot is going on inside of you as you go about your daily business -- and as you sip that hot bean juice to try to chase off the Sandman!

I'm of course curious as to what plants use the caffeine alkaloid for, why they evolved it, since of course they don't need to worry about staying awake.