May I ask how many people have already submitted for each character and which chracters are still needed the most? :)

Well... It's okay... But it doesn't really teach me more than the deeper you get under water, the less oxygen there is and the lower the heart rate gets and the lunge volume... And that can be taught in one sentence...

Now to the points that you can make better:

First of all, what's up with that "Partial Pressure of Oxygen"? Is it the partial pressure of oxygen in the water or in the lungs? And does the bar mean "the redder it is" the more oxygen there is?! Or the other way around? Also a scale would be helpful.. And if I were you, I'd name the tabs or do not make tabs at all, since it makes the comparison between heart+lunge with the partial pressure of oxygen harder...

Also it would have been much more fun to make it into a real game:
Like you could control the whale and the faster you get to a certain finish line without dying makes you win and to get your lungs filled with water again you need to dive up! You could also add some plankton that the whale can eat for some extra points and some obstacles that the whale has to avoid or he'll get minus points or even die! And... get some better artists...

Is it just me that I die everytime in this game? xD
I can't make it further than level 3 which kind of frustrates me ^^' And makes the game less addicting to me D:
Also, I don't if it just lags when I jump or if it's a slow motion then O.o But it makes the gameplay even harder D:
I wish I could have made it further than level3, I would have liked to see more levels ^^' Nevertheless, nice game! C:

This Game is damn addicting! D: