Photosynthesis Processes. Overview Absorption of light energy – Sun hits chloroplasts Conversion to chemical energy – Light dependant reaction Storage.

Photosynthesis Processes

Overview• Absorption of light

energy– Sun hits chloroplasts

• Conversion to chemical energy– Light dependant

reaction• Storage of energy in

sugars– Light independent

reaction

2 Stages of Photosynthesis

1. Light Dependant Reaction • Takes place in Grana

(thylakoid membrane)• Products – ATP, O₂,

NADPH

2. Light Independent Reaction – Calvin Cycle• Takes place in the stroma• Products – Glucose,

NADP⁺, ADP

Light Dependant Reaction

• Takes place in thylakloid membrane of the chloroplast

Light Dependant Reaction

Light Dependant Reaction

1. Light strikes PSII– 2 electrons are excited– Simultaneously - H₂O split into to H⁺ and ½ O₂ (photolysis)

2. Electrons flow down ETC (electron transport chain) – Providing energy for production of ATP– Electrons enter photosystem I

3. Light strikes PSI– Exciting electrons

4. Electrons flow down to NADP⁺ electron acceptor– Provide energy for production of NADPH (used in light

independent reactions)

Light Dependant Reaction

Light Independent Reactions

Calvin Cycle• No light required• Carbohydrates are

synthesized from CO₂ using the ATP and NPDH formed in light reactions

Calvin Cycle• 4 Steps

1. Carbon Fixation2. Energy conversion3. Release one

molecule of sugar G3P

4. Regeneration of RuBP

Calvin Cycle• Step 1 – Carbon Fixation– Three molecules of CO₂

combine with 5-C sugars RuBP (Ribulose biphosphate)

• Enzyme is Rubisco

– Each CO₂ forms a 6-C molecule which splits into two 3-C acids (PGA)

Calvin Cycle• Step 2 – Energy Conversion– 2 chemical reactions

Use 6 molecules of ATPATP ADP + P

AndUse 6 molecules of NAPDH

NADPH NADP⁺

– Producing 6 molecules of 3-C sugar G3P (phosphoglyeralehyde)

Calvin Cycle• Step 3 – Release one

molecule of G3P– Five of the G3P

molecules remain in the cycle

– One G3P molecule in released as a product

Calvin Cycle• Step 4 – Regeneration

of RuBP– Series of chemical

reactions• Use 3 ATP to convert

5 G3P molecules into 3 RuBP molecules

Calvin Cycle• Takes two molecules of G3P to produce one

molecule of glucose– So• 6 molecules of CO₂• 18 molecules of ATP• 12 molecules of NADPH

Photosynthesis Recap