Cyanobacteria are a diverse group of photosynthetic bacteria that were previously known as 'blue green algae'. These prokaryotes perform photosynthesis even though they do not have chloroplast. This is because they possess chlorophylls in the cytoplasm. They have flattened sac like structures called 'thylakoids' where photosynthesis actually takes place.These bacteria thus produce the energy they require from sunlight and carbon dioxide.