What part of a cell contains inner membranes arranged in stacks of membranous sacs, called Grana?

Cells contain various structures to perform certain
functions. Parts of a basic cell include the Cell Wall, Cytoplasm,
Ribosomes, and Nucleus. Animal cells differ in important
ways from Plant cells, and this question refers to a structure found only in
plants.

The most important function of a plant cell is
Photosynthesis, the mechanism by which sunlight is transformed into
energy and nutrients within the plant. To process sunlight, plant cells have structures
inside called Thylakoids. These allow photons to be absorbed from
sunlight and passed along an Electron Transport Chain to break
water molecules down and and provide to energy needed to create
ATP, the molecule that transfers energy from cell to
cell.

The Thylakoid is membrane-bound, which means it has
an organic membrane surrounding the entire structure, and is typically embedded in the
Chloroplast Stroma. Inside, it contains a
Lumen, which absorbs protons during the Light-Dependent Reaction.
Thylakoids often group together into stacks, or Grana, connected by
Thylakoid Stroma, a thick fluid used for carbohydrate production. Stacks of Thylakoids
are found inside Chloroplasts, and inside Cyanobacteria.