Final answer:
Within chloroplasts, the stacked, disc-shaped structures are known as thylakoids, which are arranged in stacks called grana. Thylakoids contain chlorophyll essential for photosynthesis, and the area around the grana is the stroma.
Step-by-step explanation:
Within the chloroplast are stacked, disc-shaped structures called thylakoids. These thylakoids are critical for the process of photosynthesis, where autotrophic eukaryotes convert light energy into chemical energy. The thylakoid is a membrane-bound structure that contains chlorophyll, the pigment responsible for capturing light energy. These disk-shaped structures are organized into stacks known as grana (singular: granum), and they are located inside the chloroplasts, which are enclosed by an outer and an inner membrane. The area surrounding the grana is known as the stroma, which is the fluid-filled space where the light-independent reactions of photosynthesis occur.