The part of a chloroplast that is not involved in the light reactions is the stroma.

Here's why:

* Light Reactions: These occur in the thylakoid membrane, which contains chlorophyll and other pigments that capture light energy. The thylakoid membrane is folded into stacks called grana.

* Stroma: This is the fluid-filled space surrounding the thylakoids. It contains enzymes and molecules necessary for the Calvin cycle, which is the dark reaction of photosynthesis.

In summary:

* Light reactions: Thylakoid membrane (grana)

* Dark reactions (Calvin cycle): Stroma