Tissues are groups of cells that work together to perform a function. Onion cells within the onion bulb are tissue used for storage. They are tightly packed together which provides strength and protection as well as maximizes the amount of materials being stored inside these cells. They have a rectangular shape. These cells in the bulb are used for the storage of energy. They are transparent because they lack chloroplasts and do not carry out photosynthesis--a process that occurs in the leaves of the plant, above-ground.However, excess sugar and starch is transported to the bulb by the vascular tissue of the veins and is stored inside the onion to be used as energy. Because onions contain large cells, they are used in biology to study plant cell structure and to observe plasmolysis.