Photosynthesis Visible Light absorption spectra What structures absorb

Photosynthesis

Visible Light: absorption spectra • What structures absorb the light? PIGMENTS • Chlorophyll a (dominant pigment) • absorbs best in red & blue wavelengths & least in green • Chlorophyll b, carotenoids, anthocyanins, xanthophylls (accessory pigments) • Why are plants green? Reflect GREEN light

Photosynthesis • Light reactions • convert solar energy to chemical energy • ATP & NADPH • Calvin cycle • sugar production reactions • Uses (ATP & NADPH) to reduce CO 2 & synthesize C 6 H 12 O 6 It’s the Dark Reactions!

Light Reaction • Absorbs light to excite electrons • Oxidation of H 2 O forming O 2 (Photolysis!) • Electrons replaced • H+ concentration building • Oxygen is released 2005 -2006

Linear Electron Flow • “Noncyclic photophosphorylation” • PS II generates energy as ATP • PS I generates energy as NADPH

Light Reaction con’t… • Electron Transport Chain • Pumps H+’s to maintain gradient • NADP+ final e- acceptor in chain = NADPH • Chemiosmosis to generate ATP • Diffusion of H+’s down gradient into Stroma 2005 -2006

Light Reaction of Photosynthesis Photosystem II Photosystem I Video

Comparing Chemiosmosis 2005 -2006

Moving on to Calvin cycle § Location: stroma § Uses products of light reactions to drive synthesis reactions u. ATP u. NADPH 2005 -2006

From CO 2 C 6 H 12 O 6 • CO 2 has very little chemical energy • fully oxidized • C 6 H 12 O 6 contains a lot of chemical energy • reduced • endergonic • Reduction of CO 2 C 6 H 12 O 6 proceeds in many small steps • each catalyzed by specific enzyme

(3 CO 2 enter one at a time) Calvin cycle 3. Regeneration of Ru. BP 3 ATP PGAL to make glucose sucrose cellulose etc. 6 NADPH 6 NADP 5 C CO 2 1. Carbon fixation Rubisco -enzyme that Binds CO 2 to Ru. BP 3 ADP PGAL 1 C ribulose bisphosphate 6 C 2 x 3 C 3 C x 2 2. Reduction 2 x 3 C PGA 6 ATP 6 ADP

Calvin cycle § 6 turns of Calvin Cycle = 1 glucose u 6 CO 2 is needed u 18 ATP is needed u 12 NADPH is needed § PGAL important intermediate! ucan be used to make: § Glucose, sucrose, lipids, amino acids etc.

Summary • Light reactions • • produced ATP produced NADPH consumed H 2 O produced O 2 as by product • Calvin cycle • • consumed CO 2 produced Glucose regenerated ADP regenerated NADP

Factors that affect Photosynthesis • Enzymes are responsible for several photosynthetic processes, therefore, temperature and p. H can affect the rate of photosynthesis. • The amount and type of light can affect the rate. • A shortage of any of the reactants, CO 2 and/or H 2 O, can affect the rate.

Energy Cycle sun Photosynthesis CO 2 H 2 O glucose Cellular Respiration The Great Circle of Life! Where’s Mufasa? ATP O 2