13. how do a carbon atom's available electrons allow it to form biological
macromolecules?

The fundamental component for all of these macromolecules is carbon. The carbon atom has unique properties that allow it to form covalent bonds to as many as four different atoms, making this versatile element ideal to serve as the basic structural component, or “backbone,” of the macromolecules.

Explanation:

The nature of photosynthesis is C) an energy-releasing proces. During photosynthesis, molecules are released that the plant will then feed upon to enable it to be able to grow. In this process, the form of energy produces comes with the substance glucose, which is necessary for further processes allowing the plant to grow and repair itself to take place.