Answer:
A stack of thylakoids is called a grana.
Step-by-step explanation:
Thylakoids are flattened, membrane-bound structures found within the chloroplasts of plant cells and some photosynthetic bacteria. They contain the pigments and other molecules necessary for the process of photosynthesis.
A grana is formed when multiple thylakoids stack on top of each other. These stacks are connected by intergranal lamellae, which are extensions of thylakoid membranes that link adjacent grana together.
The arrangement of thylakoids into grana is important for the efficiency of photosynthesis. It increases the surface area available for light absorption and provides a structured organization for the flow of electrons and energy during the light-dependent reactions of photosynthesis.
In summary, a stack of thylakoids is called a grana. This organization of thylakoids plays a vital role in the process of photosynthesis by providing an efficient structure for light absorption and electron transport.