Grana are stacks of structures known as thylakoids. Thylakoids are sac like membrane-bound structures which are embedded within the chloroplast stroma of plants and green algae. The thylakoids is the site of the light reactions of photosynthesis and it functions by trapping the energy from sunlight during photosynthesis. The high surface area of the thylakoids maximizes the amount of photosynthesis that can take place.
