˙˙00˙ ˙00˙01˙03˙01The Membrane Equivalence Affair˙00 ˙ ˙01˙Om du tror att du träffat alla biologer för att du träffat en biolog, då har du inte träffat många biologer.˙ ˙00 ˙ ˙03˙02PUH / AGONY ˙02˙01˙01˙00˙ ˙01Facing my first written exam (test, that is) during my biology studies, I spent the better part of two weeks in front of my books, only to find that one five-point question of the test was based on things that we were not supposed to know. As if this wasn't enough, the question itself was written in such a way that perhaps is funny if you are a sixty-year old university teacher and your name is Conny, but hardly else. This is how it all turned out... (the following paragraphs were translated from Swedish in such a way that everything was left intact, if you know what I mean) ˙027. Vera performs a laboration during her biology studies. In the microscope, she can see how plasmolysis is developed within the cells of the onion tissue the vacuoles of which contain much antocyanin (which is a pigment). Vera is so fascinated by her studies that she decides to spent her night right there, at the laboratory, and perform some extra tests on the onion cells. What she does first is that she let the cells undergo plasmolysis in a 0.24 M NaCl-solution. She then study them carefully in the microscope. After that she puts the pieces of tissue in a solution of 55 % glycerol of exactly the same osmotic potential as that of the 0.24 M NaCl-solution. She then glances at the tissue every five minutes. What will she see? How can she explain what she sees? Given is that glycerol is a small, neutral molecule that slowly crosses natural membranes. ˙01My answer: ˙021.˙01 Vera, fascinated as she is, studies how the vacuoles slowly shrink as the water leaves them in the 0.24 M NaCl-solution, and she remembered how happy the cells looked before, when they floated around in pure water. At that time, the vacuoles used up almost a hundred percent of the cell's volume by merely existing. Now, in the salt water, water has left the cell in order to try to bring equity to the system, and the vacuoles have, accordingly, shrunk a great deal. Vera can see that the cell does not feel very well and that it is sad. ˙022.˙01 "I know!", Vera cried out loud, "I put the onion tissue in glycerol instead. That will perhaps make the cells happy again!" And, fuck me, ˙they were˙ ˙00! Slowly the cells started to regain their so sadly lost domains, and after a while, they started to look normal again. ˙023.˙01 "But... why?", Vera wondered. She let her thoughts wander back to Conny's lessons, but no matter how she tried, she could not remember that the old, wilden man had said anything at all about this. "Fuck!", she said, "He left us without any could how to solve this problem! Guess I am better away without that old haggard, anyway!" Hmm... The cells, Vera thought, are put into a solution with a lot of small glycerol molecules, and it would be a nice thing for the cell to do to try to bring equity to the concentration scale. Accordingly, the small, uncharged and non-polar glycerol molecule finds its was across the plasma membrane of the cell, and does so in such quantities that some kind of equity is reached. ˙024.˙01 "But... What about that NaCl anyway?", Vera thought. "Or maybe... Yeah, that must be it! NaCl (aq) consists of Na+ and Cl-, and they cannot penetrate a plasma membrane due to their electric charge (Bokanns' charge- and ion rule). "Question is if the salt found its way into the cell at all. Maybe it was enough for the cell to lower its water content dramatically, and that the natural cell salt then reached such a great volume concentration ratio that the osmotic potential inside the cell was about the same as the one outside it. When I then put the cells into the glycerol-solution, the cells imported so much water that the difference in concentration was levelled. Water can, thanks to its size and in spite of its polarity, penetrate plasma membranes. Yeah, that's the way it must be!", Vera cried out in happiness. ˙02Teacher comment: Is this your idea of humour? Because if it is, then perhaps you should try to conceal it, as I found it deeply insulting. I have given you five points out of five, but if I had the power to lower that, I would have done it without any doubt. ˙01Puh comment: The naughty professor will probably think twice before he messes with an Agony member again. ˙01