Structure of chloroplast

     The chloroplast are bounded by two unit membranes, an outer and inner lipoprotenious membranes with an inter membrane space between them. The inter membrane encloses stroma or matrix which is denser, colorless and granular ground substance. The stroma are mainly formed of proteins (more than 50%) and  also 70’s ribosome (plastido-ribosome), circular and naked DNA molecules (0.5%) , mRNA and tRNA molecules, water , minerals (mn⁺⁺, Fe⁺⁺, Mg⁺⁺) and enzymes. It is the site of dark reactions of the photosynthesis.

                                                    In the stomata, small structures called grana and inter grana  connecting membranes remain embedded. Each granum consists of disc-shaped membranous sacs called thylaknoid piled one upon others. The granas are connected to each other by a network of membranous tubules known as the intergrana or stroma lamallae or frets. The thylaknoid membrane contains all the enzymatic quantasomes components required for photosynthesis. They are the site of light reactions. Interaction between chlorophyll  and other components takes place within the thylaknoid membrane. Like mitochondria, chloroplasts are semi-autonomous cell organelles because they have complete machinery to synthesize some of required proteins while for some other proteins , these depend upon nuclear DNA and cytoplasmic ribosome.