Cyanobacteria are unicellular prokaryotic organisms. Besides, some primitive cellular cell organelles, they have photosynthetic lamellae where photosynthetic pigments like chlorophyll- $a c$, phycocyanin and phycoerythrin, are present.
These coloured pigments confer typical blue green colour to the bacteria and enable them to manufacture food for themselves and aquatic animals. Green plants are multicellular are organisms, which is capable of making food by using $\mathrm{CO}_2, \mathrm{H}_2 \mathrm{O}$ and light energy in specialized cell organelles called chloroplast. So bacteria and green plants make food for living organisms on earth.