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Published byMalcolm Rogers Modified over 9 years ago
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Photosynthesis Light-Dependent Reactions
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Importance of Leaves Most photosynthesis occurs in the leaves.
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Photosynthesis Converting energy from sunlight into chemical energy.
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Pigments Absorb Wavelengths of Light
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Absorption Spectrum Other pigments are called ACCESSORY pigments. Chlorophyll is the main photosynthetic pigment
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Action Spectrum Shows which wavelengths are actually the most useful for photosynthesis
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Photosynthesis Takes Place in Two Stages: Light-Dependent Reactions – Capturing light energy Light-Independent Reactions – Carbon fixation making sugars
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Light-Dependent Reactions ELECTRON TRANSPORT CHAIN
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Photosystems Clusters of photosynthetic pigments
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Photosystems Photosystem II (PII) – Contains chlorophyll a – Absorbs 680nm λ Photosystem I (PI) – Contains chlorophyll b – Absorbs 700nm λ
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Light-Dependent Reactions Photons of light excite electrons in PII – These electrons are “photoactivated” Photoactivated electrons from chlorophyll are passed to primary electron acceptor.
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Light-Dependent Reactions Primary electron acceptor passes photoactivated electrons to ETC.
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Light-Dependent Reactions Photolysis = splitting of water with light – The released electrons from water are donated to PII as replacement electrons. H 2 O 2H + + ½ O 2 + 2e - O 2 is produced!
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Photolysis:
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Chemiosmosis As electrons are passed along ETC, a H + gradient is created in the thylakoid space.
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Photophosphorylation ATP Synthase creates ATP when the protons move down their concentration gradients, back into the stroma.
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Light-Dependent Reactions Photons are also absorbed by PI – Electrons are photoactivated go to ETC – Electrons from first ETC replace electrons lost at PI
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Light-Dependent Reactions At the end of the ETC, electron pairs bind with NADP + and H + in the stroma to form NADPH. NADPH is an electron carrier
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Noncyclic Photophosphorylation Includes both photosystems (I and II) Both ATP and NADPH are produced
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Cyclic Photophosphorylation Sometimes NADP + levels are low PII can’t pass electrons to PI – It passes them BACK to photosystem II – Continues to make ATP, but not NADPH
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Light-Dependent Reactions
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SUMMARY of Light Reactions Energy comes from ___________________________ Electrons come from _________________________ H 2 O comes from _____________________________ O 2 comes from ______________________________ O 2 goes to __________________________________ H + comes from ______________________________ ATP comes from _____________________________ ATP goes to _________________________________ NADPH comes from __________________________ NADPH goes to ______________________________
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