It would be the start up of iron. Causing it to be a reactant and spread it across.
In most plants, the leaves are the main food factories. They capture the sun's energy with the help of chlorophyll in the leaf cells. The chlorophyll traps and packages the energy from the light of the sun in a process called photosynthesis. Leaves usually have a large surface so they can collect the most sunlight.
I've looked us up ever since you posted it the only thing I can come up with is letter A because it talks a lot about Mountain chains that talks a lot about the ocean floor and the Hawaiian stuff so try a