Nitrogen enters the food 1. primarily through soil-dwelling bacteria that "fix" nitrogen by attaching it to other atoms 2. from the atmosphere when "fixed" by the photosynthetic machinery of plants 3. when rocks dissolved by rainwater become soil, which is then utilized for plant growth 4. through soil erosion followed by runoff into streams and ponds 5. through methane, produced by herbivores as a by-product of the breakdown of plant material.

The correct answer will be Option-1.

Explanation:

Nitrogen fixation is the process by which the atmospheric nitrogen enters the living sphere of the earth. The atmosphere is the largest reservoir of nitrogen in which nitrogen accounts for 78% of the total gases.

The atmospheric nitrogen is fixed through three pathways: lightning, man-made a method like Haber's process and the Biological fixation.

Biological fixation accounts fro 92% of the total nitrogen fixation which is performed by the few bacteria which contains the Nitrogenase enzyme and break down the N₂ to NH₃. The bacteria like Rhizobium is the leguminous bacteria which fixes the nitrogen.

Thus, Option-1 is the correct answer.

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