This symbiotic relationship provides support for the theory of endosymbiosis, which states tha

As the question is incomplete, let's discuss about the theory of endosymbiosis generally.

The theory of endosymbiosis states the eukaryotic cells developed from prokaryotic cells.

This theory explains that organelles like chloroplasts and mitochondria existed as individual prokaryotic cells before. The larger cells engulfed the smaller prokaryotic cells as a result of which eukaryotic cells were produced. The organelles like mitochondria have their own DNA and can produce their own proteins which support this hypothesis.

affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.