To be fair he is perhaps best known as a chemist. However he made observations that led to the discovery of one of life's essential chemical reactions. Reading up on the guy reveals a fascinating history. He also invented a very popular type of drink and a whole host of other things. A good old fashioned scientist - the type that should still be encouraged still but unfortunately can't due to academic structure almost selecting against it.
As for last week's biologist, it was none other than Galen. It's hard to convey his importance in terms of his impact on physiology and anatomy. Equally important was that he was one of the earliest examples of applying scientific method (Observation, theory and experimentation) to biology and published a work on how the "best physician is also a philosopher". Galen also pretty much came up with the concept of model organisms in terms of dissection and vivisection of pigs and primates to understand human anatomy because dissection was outlawed in Rome at the time.
He also made groundbreaking and lasting discoveries in neurology and established that the brain and central nervous system control motor function. He also described the function of agonists and antagonists on nerves so was a very early pharmacologist.He was also a damn good surgeon (probably because he practised on animals) and could even remove cataracts! Sadly a lot of his techniques were forgotten for several hundred years. Good proof that his observations on diet and hygiene is the fact that he lived until the age of 87 which is pretty good going for someone in the second century.