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8.6 gather and process information from secondary sources to identify and explain the location of the sites of light absorption and the site of the Calvin cycle

gather and process information from secondary sources to identify and explain the location of the sites of light absorption and the site of the Calvin cycle

Useful information

  • The light dependent reaction occurs in the thylakoid membrane where the photosynthetic units are found. The chlorophyll and accessory pigments that capture light energy (antenna complex and reaction centres) are localised within the thylakoid membrane.
  • The electron transport chain that connects photosystem II and photosystem I is also embedded in the thylakoid membrane. Photosystem II splits water and feeds electrons into the electron transport chain. The electrons are activated and used by photosystem I to make NADPH for use in the Calvin Cycle.
  • During this process hydrogen ions are transferred from the stroma side of the thylakoid membrane to the lumen (or inside) of the thylakoid. The protons are then used for the synthesis of ATP using the chemiosmotic theory. ATP synthase is situated in the thylakoid membrane and uses the electrochemical gradient provided by the flow of protons back to the stroma to make ATP from ADP and Pi. ATP synthesis does not occur if no membranes are present.
  • The light independent reaction or Calvin Cycle occurs in the stroma. The thylakoid membranes are “sided”. The ATP and NADPH produced by the light dependent reactions are produced on the outside of the thylakoid; they are released into the stroma.
  • The Calvin Cycle uses 18 ATP available in the matrix of the stroma, 12 to phosphorylate 3-phosphoglycerate and six to regenerate the 5-carbon acceptor. The 12 NADPH released to the stroma side of the thylakoid membrane supplies H+ ions to replace the phosphate group provided by ATP and form glyceraldehyde phosphate.

Here is a site to start with

Calvin cycle (external website) J Kimball, USA.