To convert inorganic carbon or nitrogen into stable, organic compounds that can be assimilated into organisms. Photosynthetic organisms such as green plants fix carbon in carbohydrates as food; certain bacteria fix nitrogen as ammonia that can be absorbed directly or through nitrification by plant roots. See more at carbon fixation, nitrogen fixation.
To convert a substance, especially a gas, into solid or liquid form by chemical reactions.
To kill and preserve a tissue specimen rapidly to retain as nearly as possible the characteristics it had in the living body.