Yes plastids are present only in plant cell they are not present in animal cell,the work of plastids is to give green colour to plants.It is responsible for photosynthesis in plants,there is no need of such organ in animals because animals rely on external factors to get their food, they do not need to photosynthesize, or, make their own food. Plastids have chromoplasts, chloroplasts and leucoplasts, of which chloroplasts store chlorophyll, a chemical required by plants to photosynthesize.