Can you explain how photosynthesis works?
user
Photosynthesis is a process where carbon dioxide and water are transformed into glucose and oxygen. The plant can then stores energy in the glucose and release the oxygen back into the air.
Photosynthesis can be split into two stages, light-dependent reactions and the Calvin cycle (light-independent reactions). 
##### The light-dependent reactions
The light-dependent reactions take place within the thylakoid membrane and are made up of two reactions occurring at photosystem II (PSII) and photosystem I (PSI) respectively. They produce ATP and NADPH for glucose production in light-independent reactions, as well as the oxygen photosynthesis releases, using the energy of light. The reactions can be described as
```
2H2O + 2NADP+ + 3ADP + 3Pi → O2 + 2H+ + 2NADPH + 3ATP
```

- PSII

The pigments in PSII absorb photons, passing the energy inwards between them until it reaches the reaction center to boost an electron to a high energy level. The high-energy electron is passed through an electron transport chain, spending some of its energy driving the pumping of H+ ions from the stroma into the thylakoid interior. This lost electron in PSI is replaced with one from water, forming the oxygen that photosynthesis releases and H+ ions, which then join the pumped-in ions. As the ions flow down their gradient and into the stroma, they pass through ATP synthase, driving ATP production.

- PSI

The pigments in PSI also absorb photons to boost a high-energy electron, passing it down a shorter electron transport chain to NADP+ to make NADPH. The electron in PSII is replaced by the electron passed down from PSII.

##### The Calvin cycle
The Calvin cycle occurs in the stroma, or the fluid-filled region outside the thylakoid membranes. It uses the chemical energy of ATP and reducing power of NADPH from the light-dependent reactions to produce sugar from CO2:
```
3CO2 + 6NADPH + 6H+ + 9ATP + 5H2O → G3P + 6NADP+ + 9ADP + 8Pi
```
It consists of 3 stages:

1. Carbon fixation
A CO2 molecule is combined with a five-carbon acceptor molecule called RuBP to make a six-carbon compound, which then splits into two molecules of a three-carbon compound, 3-PGA.
2. Reduction
ATP and NADPH are used to convert the 3-PGA molecules into three-carbon sugar molecules called G3P. NADPH donates electrons to, or reduces, a three-carbon intermediate in this stage, giving it the name "reduction". The NADPH and ATP then become NADP+ and are put back into the light-dependent reactions.
3. Regeneration
One of every 6 G3P molecules is used to produce glucose, while the other 5 are recycled to replace the consumed RuBP in stage 1. The regeneration also requires ATP and returns the ADP to the light-dependent reactions.
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