Tuesday 12 November 2013

Bloody hypothesis testing

Testing hypotheses is at the very heart of science, so it's curious that they don't feature at all in early-year college science education.

This is how it works in real science. You notice something peculiar about the natural world; you wonder why things might be like that; you have an idea that seems to explain the phenomenon (that's your hypothesis).  It is your duty as a scientist to push that hypothesis very hard to see if it will fall over. So you design some experiments to "test your hypothesis" rather than experiments that serve to confirm your prior convictions. That's very difficult to do because we really cherish our creative insights. We are blinded by prejudice, limited in our experience, and may lack the equipment to perform the key experiments, so it's a good idea to have other people critically evaluate our hypotheses and we can return the compliment. "The most exciting phrase to hear in science, the one that heralds the most discoveries, is not "Eureka!" but "That's funny.""

This is how it works in introductory science classes.  You're told that some great person made an observation, probably a long time ago; he knew instantly why it happened like that; he carried out some clever experiments that proved for all time what the true explanation was and is.  There was no error if estimate in those classic experiments.  You-the-student clearly have a brain the size of a peanut rather than a planet, so you're tasked to repeat what the Great Man did and be darned sure you get the 'right' answer  . . . or someone will give you a zero mark.  If that's all your experience of science, then you learn bugger-all about the natural world; you get no practice in your ability to think things through; you can't learn from mistakes because you're not allowed to make any; and you're never encouraged to understand how you can apply any outcomes to different but similar situations in the real world.

There is a certain amount of justification in having some of this in an introductory course:  at 18 you're so plug-ignorant (not stupid, that's independent) that you need to be told about some of the key concepts discovered by Hooke and Newton (and Hamilton and Boole if you happen to be studenting in Ireland).  You need to practice and practice again using some of the standard equipment, so your hands take on some of the burden of thinking.  But you also need to know and internalise that your ideas are as good as anyone else's, and you need to commit to those ideas and defend them rhetorically while at the same time challenging them with data.

This week's 1st Year Cell Biology task was to see what happens to cells when they are exposed to solutions that (cue the Three Bears theme) are more salty, less salty and just right.  In science-speak we say hypertonic, hypotonic and isotonic. This is a highly reproducible experiment - you get the same result whether you're in Vietnam or in Vermont.  The result hinges on the fact that cells are bounded by a semi-permeable membrane - some things, notably and especially water, can move free across this membrane whereas things dissolved in the water generally cannot cross it.  A convenient and accessible source of fresh cells is human blood - all you need is a drop of that, a microscope and the three-bears different solutions. People tell the students what will happen as a catechism.  Not: Q. How do you know that you have a soul? A. Because the Bible tells me so. But rather: water travels from a greater concentration to a lesser or is it water travels from a lesser concentration to a greater? Dang! I can't remember because I haven't repeated it often enough.  

Back in January I forced my students to make a calculation and write the answer down in ink in their immutable and holy lab book.  Giving them a chance to be wrong and thereby giving them an opportunity to learn.  Even when I told them that the sky would not fall if they got the wrong answer a substantial minority felt and looked deeply unhappy about this arrangement. This week it was similar.  The current cohort of students have "covered" osmosis and semi-permeable membranes and several of them were able to quote a catechism of concentration with such fervour and conviction that I started to believe it myself.  So I asked them to think a bit and then set out a hypothesis about whether a red blood cell, when immersed in a hypertonic solution, will a) shrink b) inflate c) stay the same d) burst e) turn blue or f) sing the marseillaise.  And I compelled the poor young people to write it down in ink at the top of the next page in their lab-books.  
THEN we could start making some observations to test our hypotheses.
See below for the answer!!!!: 

Picture credit: http://url.ie/jxdg

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