Photosynthesis / Cellular Respiration

Where do Light Reactions and Dark Reactions occur?

• They both occur in the Chloroplasts

  • Light Reactions

    • Occur in the Thylakoids

  • Dark Reactions

    • Occur in the Stroma

What are light Reactions?

• A sequence of reactions that use sunlight and water to produce ATP and NADPH for use in the Calvin Cycle ( Dark Reactions ).

What are the products / by-products of Light Reactions Photolysis?

• The energy created is ATP and NADPH - products

• Oxygen ( O2 ) - by-products

What is the process of Light Reactions / Photolysis? ( 5 Steps ) ( First Reaction )

• Step 1: Photosystem II

  • Light strikes the chlorophyll, exciting the electrons which are used to power the rest of the process.

  • Splits Water (H2O ) into H+ ions and O2

• Step 2: 1st Electron Transport Chain ( ETC )

  • Pumps the Hydrogen Ions ( H+ ) from the Stroma into the Thylakoid.

    • H+ ions converts later into ATP.

• Step 3: Photosystem I

  • Light strikes the chlorophyll again, recharging the electrons for Step 4.

• Step 4: 2nd Electron Transport Chain ( ETC ) 

  • Recharged electrons are used to make NADPH for the Calvin Cycle ( Dark Reactions ).

• Step 5: ATP Synthase Channel

  • Enzymes pump the H+ ions that were in the Thylakoid back into the Stroma. Uses the energy created to make ATP for the Calvin Cycle ( Dark Reaction ).

What is the process of Dark Reactions / Light Independent? ( 3 Steps ) ( Second Reaction )

• Step 1: Carbon Fixation

  • 3 molecules of CO2 enters, one Carbon atom from each Carbon Dioxide is added a 5-Carbon sugar ( Ribulose Biphosphate ( RuBP ) )

    • Makes a 6-Carbon molecule

• Step 2: Chemical Reshuffling ( Reduction )

  • Set of reactions involving ATP and NADPH to form 3-Carbon molecules ( PGAL / G3P )

• Step 3: Regeneration

  • PGAL molecules that do not leave are reformed into RuBP through the usage of ATP.

What are the products / by-products of Dark Reactions?

• The energy released is ADP and NADP+ which is fed back into the Light Reactions. - by-product

• Glucose - product.