Chloroplasts in mesophyll cells of leaf. Coloured Transmission Electron Micrograph (TEM) of meso- phyll cells in a young leaf of Zinnia elegans. These cells contain large numbers of chloroplasts (green), and are therefore active centres of photosynthesis. The chloroplasts are situated on the edge of each cell; starch granules (pink) inside them are a form of stored sugar. At the centre of each cell is a large vacuole (blue) filled with cell sap. The nucleus is coloured red. Mesophyll cells are loosely arranged cells in the leaf, with large air spaces (white) between them, allowing for gas exchange during photosynthesis. Magnification: x2,000 at 6x4.5cm size.