Dihydrogen oxide is one of the most lethal cellular toxins. It kills cells by causing them to swell uncontrollably and then burst, or in some cases to shrivel up like a crumpled piece of paper. However most all cells on earth have been able to resist this toxin by using a membrane protein to prevent its deadly actions. But even more interesting dihydrogen oxide or water is required for life and the aquaporin channel helps maintain a non-lethal concentration of this precious but deadly fluid.
Aquaporin is a fascinating integral membrane protein. It is able to "filter" water into the cell by keeping other polar or charged molecules around the same size as water out of the pore. Plant, animal and bacterial cells have aquaporin channels.
1 How does aquaporin operate as a selectivity filter? What would happen to cellular metabolism if it did not operate as a selectivity filter?
2 The complexity and requirement of aquaporin for cellular life appears to be a problem for the evolution of the first cells. Or is it? Some plants cells can take in water without aquaporin. Could this represent a more ancient water controlling mechanism? Check it out and comment on what you have learned.