This is more to do with Bioaccumulation of mercury, where the mercury is absorbed into the issue of animals, and so animals higher in the food chain consume a lot of tissue matter hence increasing mercury content in their system.
The study of all chemicals containing carbon is organic chemistry.
The higher levels of gravity put on an object the more weight the object has. For example someone who weighs say 100 lbs would weigh more if higher amounts of gravity would be applied to them. And less if less gravity was applied. But larger objects will automatically have more gravity applied to them than something smaller due to the gravitational pull needing to pull harder to keep the object to the planet's surface. Hope this helps! :)