Final answer:
The arrow points to the thylakoids in a chloroplast, which are stacked into grana, and surround an area called the stroma.
Step-by-step explanation:
The arrow in the question likely points to the structures in a chloroplast known as thylakoids, which are disc-shaped, membrane-bound structures where the light-dependent reactions of photosynthesis take place. A stack of these thylakoids is referred to as a granum. Within the chloroplast, the thylakoid membrane encloses an internal space known as the thylakoid lumen, while the liquid-filled space surrounding the grana is called the stroma. The initial interaction between light and plant material starts with chlorophyll, a pigment embedded in the thylakoid membrane that gives plants their green color.