How is light energy processed in the light reaction of photosynthesis?

Answer 1

In simple terms, photosynthesis is the conversion of carbon dioxide (CO2) to carbohydrate (CH2O). To do this two things are needed: energy to drive the reaction and a source of hydrogen.

The light reaction of photosynthesis produces two essential substances: ATP and NADPH. ATP provides the energy for the conversion of CO2 to CH2O, and NADPH provides the hydrogen.

The light reaction depends on groups of chlorophyll molecules, called photosystems, absorbing light energy. The energy is used to eject high energy electrons from the chlorophyll. The energy in the electrons is then used to make ATP and NADPH.

There are two photosystems, called photosystem I (PSI) and photosystem II (PSII), which work in sequence. (PSII comes before PSI in the sequence, but they were discovered and named in the reverse order!).

PSII absorbs light and emits a high energy electron. The energetic electron then passes down a series of molecules, called an electron transport chain (ETC), releasing energy as it goes (you can visualise it as a ball bouncing down a set of stairs, losing energy as it falls). The energy released is used to make the energy carrier compound ATP.

To replace the electrons lost from chlorophyll in PSII water (H2O) is split into hydrogen ions (H+), electrons (e-) and oxygen atoms (O):

H2O = 2H+ + 2e- + O

This is the source of the oxygen released by photosynthesis.

The second photosystem, PSI, also absorbs light and emits a high energy electron from chlorophyll. The energy in this electron is used to drive the synthesis of NADPH from NADP+ ,hydrogen ions (H+) and electrons (e-):

NADP+ + 2H+ + 2e- = NADPH + H+

The hydrogen ions needed for this come from the water which was split by PSII.

The electrons lost from the chlorophyll in PSI are replaced by the electrons ejected from PSII.

The result of all this is that light energy is converted into chemical energy in ATP, water is split to provide the hydrogen needed to make NADPH, and oxygen is released as a waste product.

The ATP and NADPH are then used in the light independent reaction (the Calvin cycle) to concert carbon dioxide into carbohydrate.

Answer 2

The process of renewing biological energy molecules like ATP and NADPHbe the harnessing of sunlight is called photosynthesis. The energy capture and conversion is mediated in the first step by chlorophyll in green plants.

Answer 3

Yes. ATP is used in the cell for quick energy by breaking the bond between the 2nd and 3rd phosphate group. NADPH is used to carry high-energy electrons. The energy is used to run the Calvin Cycle.

Answer 4

It is happening in firct phase. It is storing energy.

Answer 5

Light Reaction(s)

Answer 6

Light Reaction

Answer 7

through an electron transport chain