If you monitor your practice run you can see how much your improved time wise.
The answer is 2000 calories. My guess is that is because you need to burn so many but gain so many to get energy. This is a way to not gain weight.
I dont know but it may be urinary system as you need liquid to urinate so that propably includes kidny i am assuming and if you dont get water or get dehydratd and can cuase serous kidney issues thats why i think it is urinary system