DENDROLOGY

Detailed explanation-1: -The light reaction occurs in the thylakoid membrane of organelles called chloroplasts in plants.-Chlorophyll in the Photosystems I and II retain a light, which triggers the arrival of high energy electrons (photoactivation).

Detailed explanation-2: -Physically, photosystems are found in the thylakoid membranes. There are two kinds of photosystems: photosystem I (PSI) and photosystem II (PSII) (Fig. 3.3). PSII acts first during the light transformation process in photosynthesis, but it was named PSII because it was discovered second.

Detailed explanation-3: -Chlorophyll a within the photosystem II (PS II) absorbs a photon of light (most efficient at 680 nm). This photon of light excites an electron from the chlorophyll a molecule to a higher energy state. The chlorophyll is now in a photoactivated state.

Detailed explanation-4: -The electrons must travel through special proteins stuck in the thylakoid membrane. They go through the first special protein (the photosystem II protein) and down the electron transport chain. Then they pass through a second special protein (photosystem I protein).

Detailed explanation-5: -Photoactivation is the last step in the assembly of Photosystem II before it becomes functional. The exact Cd2+ concentration necessary for inhibition depended on the concentration of calcium. It is proposed that Cd2+ binds competitively to the essential Ca2+ site in Photosystem II during photoactivation.