Photosynthesis

• occurs in 2 parts- The light reactions and the Calvin Cycle.

The light reactions

CO2 + H2O + light energy (CH2O) + O2

• The light cycle is dependent on light.Within the chloroplast, are sacs of organelles called thylakoids. (A stacked bundle of these are called Granum.)

• The Thylakoids membranes contain chlorophyll. The chlorophyll is a pigment that absorbs the light from the sun

Steps of the light reactions.

1.)The light absorbed by chlorophyll causes a transfer of electrons and H+ from H20 molecules already present. This causes the H20 to split into molecular 0xygen (02) and a H+ ion.

2) The O2 is released (we breathe it) and the H + bonds to NADP + creating NADPH

3) ATP is formed (ADP gets a phosphate group added to it creating ATP)

4)The NADPH and the ATP created here go on to fuel the reactions in the second part of photosynthesis

Steps of the Calvin Cycle

6CO2 + 6H2O + light energy C6H12O6)+ 6O2

• The Calvin Cycle is the second stage of photosynthesis

• takes place in the stroma of the chloroplast

• can occur without the presence of sunlight.

• carbon molecules from CO2 are fixed into glucose (C6H12O6)

• Process known as carbon fixation

Step 1 (simplified)1) CO2 comes into stroma from the

cytosol2) fixed with a 5 carbon molecule

making a 6 carbon molecule3) Gets split into two 3C molecules

called PGA

Step 21) The 2 PGA molecules get

phosphate from splitting of ATP2) Forms PGAL (still only 3C), and

most importantly3) An organic molecule (like

glucose)

• Also forms ADP, NADP+ and phosphate

• These can be used again in future light reactions

Step 3• Most PGAL converted back to a 5C

molecule• (remember the Calvin Cycle

begins with a 5C molecule & one CO2 molecule)