Question

2, In which part of the Chloroplast ( be very specific ).......

Are the pigment molecules found?

Is there a high concentration of protons?

Does the Calvin Cycle occur?

Is an ETC found?

Is there a basic pH?

Answer 1

Chloroplasts are the green plastids occur in all the green parts of the plant and actual sites of photosynthesis. Each chloroplast is an organelle wrapped with a double membrane, acting as a selective barrier for the movement of cellular metabolites into or out of the chloroplasts. It encloses a liquid proteinaceous matrix called stroma. The stroma is the site of dark reaction of photosynthesis (possess enzymes for calvin cycle). The membranous system within the stroma forms flattened bag like lamellae called thylakoids. These thylakoids are of two types Stroma thylakoids (facing towards stroma) and grana thylakoids (attached with each other). Thylakoid membrane possess photosynthetic pigments which are clustered together forms a photosystems. These are of two types: photosystem I and photosystem II. There main function is to perform photosynthetic light reaction. The pigments and other factors of light reaction are usually located in thylakoid membranes. Photosystem I is located only in stroma thylakoids and non-appressed regions of thylakoids, while photosystem II occurs in the appressed or partition regions of thylakoids. Components of photosystems, consisting of reaction centres, antenna pigment molecules and electron transport molecules are associated with integral membrane proteins. In addition, thyllakoids also possess cyt b6f complex and coupling factor (ATP synthase- using H⁺ ions synthesizes ATP). Cyt b6-f complexes are evenly distributed in stroma and general thylakoids.

In the photosynthetic light reaction PSII involve in photolysis of water to give H⁺ ions to lumen of grana. So it becomes more acidic than the stroma of chloroplast i.e lumen acidic pH and stroma basic pH. The electrons are transported through membrane proteins (PQ, cyt b6f complex etc) upto PSI where the NADPH is synthesized from NADP and H⁺. The protons released in lumen surface will pumped out to stroma to maintain electrical neutrality (to avoid membrane disruption). Meanwhile the energy released by Proton movement is utilized to synthesize ATP from ADP and Pi. When the assimilatory power (ATP,NADPH) is available the dark reaction( calvin cycle) occurs in stroma.