1 / 4

Photosynthesis The Light Reaction

Photosynthesis The Light Reaction. Photosynthesis takes place in the chloroplasts in areas known as photosystems Photosystems - complexes containing the pigments where light energy is harvested Chlorophyll is the main pigment in the photosystems of eukaryotic plants

Download Presentation

Photosynthesis The Light Reaction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. PhotosynthesisThe Light Reaction • Photosynthesis takes place in the chloroplasts in areas known as photosystems • Photosystems - complexes containing the pigments where light energy is harvested • Chlorophyll is the main pigment in the photosystems of eukaryotic plants • The light reaction takes place in the thylakoid membranes • The thylakoid membranes are populated by two types of photosystems (PS I & PS II). The two work together to produce ATP & NADPH (8 steps in the non-cyclic flow of electrons)

  2. Photosystem II • When a photon is absorbed by a pigment it causes an e- to move from its ground state to an excited state. • The electron (because it is unstable in its new configuration) immediately returns to its ground state releasing the stored energy. • photon energy is transferred from pigment to pigment (light harvesting complex) until it reaches the reaction center • The energy is then harvested in a reaction center where it is transferred to an electron acceptor. • Water is split • 2 H+ are produced • Moved into the inner thylakoid space where they provide the energy to produce ATP • 2 e- are given back to the P680 • O2 is produced from the split water • The excited e- is passed through an electron transport chain (ETC) to PS I • The exergonic "fall" of electrons provides energy for the synthesis of ATP along with the proton (H+) motive force created by the movement of H+ across the membrane

  3. Photosystem I • PS I absorbs a photon and donates an e- • 2 electrons from PS II fill in the space (electron hole) • Electrons captured by the reaction center are transferred down a 2nd ETC • Enzyme NADP+ reductase transfers the 2 e- to NADP+ to NADPH (requires 2 e-) • NADP+ is an electron carrier • NADPH is then transferred to the Calvin Cycle where it will be used to produce glucose

  4. Summary • Step 1 • Light absorbed by PS II splits water • 2 e- to ETC to PS I • H+ moved to create gradient to form ATP • O2 released • Step 2 • Light absorbed by PS I reenergizes e- from PS II • Energized e- passed to ETC & is used to produce NADPH • 2e- + NAD+ g NADPH • NADPH transferred to stroma to the Calvin Cycle • H+ from inner thylakoid membrane passed through ATP Synthase to make ATP • ADP + Pi g ATP

More Related