Actually, it's more subtle and more pernicious in biology. First, you make sure that your wage slaves have no marketable skills (a PhD in molecular biology is comparable to a community college graduate). Then you carefully isolate them from all perspective and knowledge of career tracks other than the academic treadmill. Finally, you dangle the PhD in front of grad students ("You can't quit now, you won't get anything! You have to hold on until you have the degree! It's all or nothing!"), until they've sunk so many years in that they aren't willing to abandon the sunk time. Then you set up a culture where ridiculous hours and inadequate support are considered normal and make the payoff for the bosses be to get as much labor out of someone as they can get before shoving them out the door to the next slave master. The behavior of your average professor towards his lab would have him slapped with lawsuits in normal work environments.