CBSE Class 9 Answered

Chloroplast is externally covered by a double membrane enclosing stroma, in which are embedded the grana, connected by lamellae. The grana consists of pigment system made up of chl-a and b, carotene and xanthophyll. The stroma contains relevant enzymes required for photosynthesis as well as DNA, RNA and cytochrome system.

Each granum is made up of disc shaped thylakoids, stacked one above the other. Each thylakoid is covered by thylakoid membrane containing quantososmes. The quantosome contains 200 to 250 molecules forming pigment system with the reaction centre in middle. It acts as a photosynthetic unit converting one quantum of light energy into chemical energy.