differentiate between tropism &trophism?

Tropism is a phenomenon where a stimulus elicits a response which is usually dependant on the direction of the stimulus involved. Hence directional responses are involved here, example: downward growth of plant roots on response to gravity. Trophism on the other hand deals with feeding strategies and habits; example: autotrophy in green plants capable of manufacturing their own food or heterotrophy that includes organisms dependant on others. Trophic levels determine the position occupied by an organism in a food chain.