(a) Cyanobacteria or blue-green algae are gram(+) photosynthetic prokaryotes which perform oxygenic photosynthesis.
(b) Cell structure is typically prokaryotic-one envelope organisation with peptidoglycan wall, naked DNA, 70 S ribosomes, devoid of membrane bound structure like endoplasmic reticulum, mitochondria, golgi bodies, plastids, lysosomes and sap vacuoles.
(c) The outer part of the protoplast contains a number of photosynthetic thylakoids. It is called as chromoplasm.
(d) Their membranes contain chlorophyll a, carotenes and xanthophylls. Chlorophyll b is absent.
(e) DNA lies coiled generally in central part of the cytoplasm known as centroplasm.
(f) Small circular DNA segments may also occur in nucleoid, known as plasmid or transposons.