Question

What is light reaction ,explain whole process​

Answer 1

Answer:

Light reactions or the photochemical phase includes light absorption, water splitting, Oxygen release, and the formation of high energy chemical intermediate, ATP and NADPH.

Several protein complexes are involved in the process.

The pigment are organized into two discrete photochemical light harvesting complexes within the photosystem.

The reaction centre is different in both the photosynthesis.

In PS the reaction centre cholophyll a has an absorption peak at 700 nm,hence P700,while PS it has absorption maxima at 680 nm and is called P680.

Answer 2

Answer:

★ LIGHT REACTION

Photosynthesis is oxidation reduction process. Here water is oxidised and carbon dioxide is reduced simultaneously. In case of light reaction water is broken to H+ and OH- generating NADPH2 and ATP. and it take place in the grana of chloroplast.

The main purpose of the light reaction is to generate organic energy molecules such as ATP and NADPH which are needed for the subsequent dark reaction.

• Chlorophyll absorbs the red and blue segment of the white light and photosynthesis occurs most efficiently at these wavelengths.
• When the light falls on the plant, the chlorophyll pigment absorbs this light and electrons in it gets excited.
• This process occurs in a complex protein system which is collectively called as a photosystem. There are two closely linked photosystems known as PSI and PSII.
• The chlorophyll pigments which are excited give up their electrons and to compensate for the loss of electrons, water is split to release four H+ ions and four electrons and O2. The electrons that are lost from the PSII enter into an electron transfer chain or ETC.
• The electrons finally reach the reaction centre where they combine with NADP+ and reduce it to NADPH
• While the electrons are taken care of, the built up of H+ ions inside the thylakoid lumen is of equal importance.
• The hydrogen ions building up inside the lumen creates a positive gradient and in the presence of the enzyme ATP synthetase, these H+ ions combine with the ADP in the nearby region to form ATP.
• The oxygen that is a waste product is released by the plant into the atmosphere and some of it is used in photorespiration if the plant needs to.

To summarise the light reaction, we can write it down as the following reaction:

2H2O + 2NADP+ + 3ADP + 3Pi → O2 + 2NADPH + 3ATP