Why must nitrogen be "fixed" before it can be used by plants?

A. Nitrogen is in the atmosphere as N₂, held together by a triple covalent bond, so that bond must be broken in order for nitrogen to be in a usable form.

B. Nitrogen is scarce in the environment and must be concentrated in order to be taken up.

C. Nitrogen is unstable, therefore needs to be fixed into a stable form before it can be used by organisms.

D. Nitrogen must be converted to a neutral molecule, as opposed to a molecule with a charge.

E. All of the above.

Nitrogen must be "fixed" before it can be used by plants because atmospheric nitrogen is held together by a triple covalent bond. This process converts nitrogen into a bioavailable form for plant absorption.

Explanation:

Nitrogen must be "fixed" before it can be used by plants because atmospheric nitrogen (N2) is held together by a triple covalent bond, making it unusable by most organisms. Nitrogen fixation is the process by which nitrogen is converted into a bioavailable form, such as ammonia (NH3), by natural or man-made processes. This conversion is necessary for plants to be able to absorb and utilize nitrogen for growth and development.