Today Quiz on Notes from last class -review before quiz (find your graphing handout with the questions) -take the quiz Midterm = cell respiration and photosynthesis

8.2 Photosynthesis: Light Dependent Reactions Photosynthesis Involves: Light Dependent Reactions – on thylakoid membrane Light Independent Reactions – in stroma Main Goal of Photosynthesis: Make glucose to use for respiration, energy, and storage

Overview of Light Dependent Reactions: (the photo part of photosynthesis) Takes place on thylakoid membrane (in chloroplasts) Involves splitting of H 2 0 for electrons Releases O 2 into atmosphere Reduces NADP + to NADPH Makes ATP from ADP by photophosphorylation Overview Animation

Steps of Light Reactions: 1.Light energy (photons) are absorbed by the pigment molecules in photosystem II. This energy is transferred to other pigment molecules until it reaches one of the chlorophyll a molecules (P680) in the reaction center. 2.The photon energy excites the chlorophyll a molecule which causes one of its electrons to gain activation energy (it reaches a higher energy state)

3.The electron from chlorophyll a is captured by the primary electron acceptor of the reaction center. Note: The electron lost by chlorophyll a will be replaced by the splitting of a water molecule by light energy (photolysis). H 2 0  2e - + 2H + + O 4. The excited electron passes from the primary acceptor down an electron transport chain losing energy at each exchange (redox reactions).

Note: The energy lost from the electrons moving down the electron transport chain drives chemiosmosis Chemiosmosis – the movement of H + ions to provide energy

5. Now, same thing but for PS I (P700) Note: The electron lost from PS I is replaced by the de- energized electron from PS II

6. Electrons move down chain until NADP reductase (final electron acceptor) then catalyzes reaction to use NADP + plus 2 electrons and 1 H + to make NADPH

Note: As all above reactions are taking place, H + ions (protons) that have been “pushed” into the thylakoid interior (lumen) diffuse back into the stroma through ATP synthase. Photophosphorylation: Use light energy to make ATP

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Review Animation before we draw the process out together