Why is biological nitrogen fixation an environmentally friendly way of fertilizing plants?
Because it is natural and does not require use of a nonrenewable resource, such as natural gas.
What is the main difference, from an energy point of view, between photosynthesis and biological nitrogen fixation?
Photosynthesis harvests and stores energy, whereas biological nitrogen fixation requires energy.
Why is a root nodule a nutritional adaptation of a plant?
A nodule results from the symbiosis between a plant and bacterium. Within nodules, the process of nitrogen fixation allows the plant to obtain nitrogen from the air.