8.3: Photosynthesis

Redox Reactions Oxidation – Loss of electrons – Loss of hydrogen atoms Reduction – Gain of electrons – Gain hydrogen atoms If one substrate becomes oxidised another becomes reduced. Oxidation and reduction always occur together. OIL RIG

Chlorophyll diagram Light dependent reaction takes place here Light independent reaction takes place here

Pigments Chloroplasts contain photosynthetic pigments to absorb light energy (chlorophyll a, b and carotene) Pigments are located in thylakoid membrane attached to proteins This is called a photosystem aka light harvesting array There are two photosystems in plants – Photosystem I (700nm wavelength) – Photosystem II (680nm wavelength)

There are two stages of photosynthesis 1.Light dependent reaction 2.Light independent reaction (aka. The Calvin cycle)

Waste product! Light dependent stage Inter membrane space of thylakoid Photon absorbed by Photosystem II Electrons are excited (result of photolysis of water) 2H 2 O  O 2 + 4H + + 4e - ETC used to generate proton gradient ATP synthase produces ATP (chemiosmosis) E - are excited again in photosystem I, NAD reductase reduces NADP+  NADPH Produce ATP & NADPH (electron carrier) Both required for Light independent reactions

-Absorb photon -Excites electrons -Excited e - pass through ETC -E - replaced by photolysis -Energy from e - pumps H + Stoma  Thylakoid = conc. gradient -ADP phosphorylated into ATP by ATP synthase -NADP reductase reduces NADP+  NADPH

dex.html Watch first 4.5 minutes of animation.

Light independent stage ATP & NADPH used to fuel reaction CO 2 is reduced into G3P 1.CO 2 attached to RuBP  2 molecules of 3-phosphoglycerate (PGA). Carbon fixation. 2.ATP & NADPH used to further reduce CO 2 into G3P 3.ATP used to reform RuBP G3P is used to form glucose, fatty acids or cellulose.

CO 2 combines with RuBP 6, 1C molecules  2, 6C molecules = 12 3C molecules (G3P). ATP and NADPH have been used to fuel these reactions 2 molecules of G3P will be converted into glucose, sucrose etc. 10 molecules of G3P, are used to regenerate RuBP so the cycle can continue.

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DBQ, pg. 396: The effect of light and dark on carbon dioxide fixation