Thylakoids are:

Thylakoids are:

• A. The outer boundary of the chloroplast
• B. A pigment that captures light
• C. The fluid inside mitochondria
• D. Flattened sacs inside the chloroplast

Answer: (D)

Chloroplasts carry out photosynthesis, and the light-dependent reactions occur on the membranes of internal sacs called thylakoids. These flattened, membrane-bound sacs are often stacked into grana to maximize surface area for the photosystems and the electron transport chain embedded in the thylakoid membranes. That arrangement makes them the structures inside the chloroplast rather than its outer boundary or a pigment, and distinct from the fluid inside mitochondria.

Chloroplasts carry out photosynthesis, and the light-dependent reactions occur on the membranes of internal sacs called thylakoids. These flattened, membrane-bound sacs are often stacked into grana to maximize surface area for the photosystems and the electron transport chain embedded in the thylakoid membranes. That arrangement makes them the structures inside the chloroplast rather than its outer boundary or a pigment, and distinct from the fluid inside mitochondria.