1. Light Independent Stage
Photosynthesis
Reaction:
2 Major Stages of Photosynthesis:
Light Dependent Stage
Light Independent Stage
Requires Light
Does not require light
Light captured by pigments in thylakoids
Often called Dark Stage (can occur in light or dark)
Makes ATP and NADPH from light
Uses products from light dependent stage (ATP & NADPH)
Uses the Electron Transport Chain to make ATP and NADPH
Series of reactions that produce Glucose
H2O is used; O2 is made(waste)
Requires CO2 to begin

2. Light Dependent Stage Steps:
Light is absorbed by pigments in Photosystem II and Photosystem I
H2O is broken down into electrons, H+ ions (protons), and O2
O2 is released, electrons pick up energy from light
Excited electrons move through the Electron Transport Chain (ETC)
Electrons lose energy along the way and are reenergized in PSI
The energy from the electrons is transferred to NADPH

3. Light Dependent Stage Steps: H+ ions from breakdown of H2O used here.
H+ ions move down the concentration gradient from one side of the thylakoid to the other through an enzyme ATP Synthase.
Called chemiosmosis
Energy released from chemiosmosis adds a phosphate to ADP to create ATP
ATP and NADPH go into the next step
The entire process of making ATP and NADPH is called Photophosphorylation

4. Light Independent Stage
Uses ATP & NADPH from Light Dependent stage
Requires the Calvin Cycle (a series of reactions)
Occurs in the stroma of the chloroplast
Requires “6 turns” of the cycle to make 1 Glucose
Carbon Fixation: takes carbon from CO2 and “fixes” them together to make glucose (C6H12O6)
Calvin Cycle requires enzymes

5. Light Independent Stage
CO2 goes into cycle & attaches to ribulose bisphosphate (RuBP)
RuBP is unstable and splits into 3-phosphoglycerate (3-PGA)
Each 3-PGA is converted into glyceraldehyde 3-phosphate (G3P)
ATP and NADPH are used as an energy source
One G3P is used to make glucose; one is saved and starts cycle again (forms RuBP)
This occurs in C3 plants; C3 for 3-carbon molecule of 3PGA.

6. Light Independent Stage
C4 Pathway:
Plants in hot, dry environments – corn, sugar cane, crabgrass
Stomata stay partially closed, lowering CO2 and raising O2 levels
Light Dep. and Indep. reactions are separated in different cells
Creates a 4 carbon compound called oxaloacetic acid
Enzyme to make oxaloacetic acid is able to work in low CO2 levels
CAM (Crassulacean Acid Metabolism) Pathway:
Plants in very dry environments
Cacti, pineapple
Reactions separated by time
Stomata only open at night to take in CO2 – loses little water

7. Photosynthesis Overview
Factors that impact the rate of Photosynthesis:
Water
Temperature
Light
CO2