Answer: The sac like structure which form the grana is called thylakoids.
Explanation: Photosynthesis in higher plants is made up of two stages: the light dependent reactions (light reactions) which occur only when plants are illuminated and the carbon fixation reactions which are driven by products of light reactions. In photosynthetic eukaryotic cells, both the light-dependent and the carbon assimilation reactions occur in the chloroplasts. A Chloroplast is a membrane bound intracellular organelle which contains many flattened membrane-surrounded vesicles or sacs called thylakoids which are usually arranged in stacks known as grana. The thylakoid membranes often called lamellae contains the photosynthetic pigments and the enzyme complexes that carry out the light dependent reactions and ATP synthesis.
