They must have the code in their genes in order to express it and they can have the code but not express the trait depending on the regulatory mechanisms which determine if the genes are turned on or off
Answer:
Image result for How is nitrogen fixation related to nitrification?
Nitrogen-fixing bacteria in the soil and within the root nodules of some plants convert nitrogen gas in the atmosphere to ammonia.
Explanation:
The Earth's interior and the sun.
If I am understanding the choices correctly, the answer would be Convection Currents.
Hope this helps!
