Photosynthesis
The Chloroplast
Before we begin, it is important that you are aware where photosynthesis is happening. Below is a diagram of a chloroplast with some key areas labeled.
Light Dependent Reaction
As hinted by the title, this part of photosynthesis requires light. When light hits the thylakoid membranes, chlorophyll pigment becomes excited by the energy and two electrons are emitted. These pass through an electron transfer chain to produce ATP in a process known as photophosphorylation [fo-to-fos-fo-riy-lay-shun].
These high energy electrons are also used to split water molecules (photolysis) this produces electrons to replace those lost by chlorophyll, and also generates hydrogen ions (or protons) and oxygen.
Electrons are picked up by NADP to make NADPH (or reduced NADP), and along with ATP, goes on to the light independent reaction.
Light Independent Reaction: Calvin Cycle
The light independent reaction takes place in the stroma of the chloroplast. At involves its very own cycle of reactions called the Calvin Cycle which is outlined below.
Carbon dioxide from the light dependent reaction enters the cycle and reacts with ribulose bisphosphate (RuBP) to make a 6 carbon compound, which is so unstable it immeadiately breaks down to two molecules of glycerate 3-phosphate (GP).
In the next step, ATP and NADPH from the previous reaction are used to reduce GP to glyceraldehyde 3-phosphate (GALP). And a sixth of this leaves the cycle to make glucose, however the rest is made in to RuBP and the cycle continues.