Photosynthesis: Life from Light AP Biology

Transcription

1 Photosynthesis: Life from Light

2 Supporting a biosphere On global scale, photosynthesis is the most important process for the continuation of life on Earth u each year photosynthesis synthesizes 160 billion tons of carbohydrate u Heterotrophs are dependent on plants as food source for fuel & raw materials

3 How are they connected? Heterotrophs and Autotrophs making energy & organic molecules from ingesting organic molecules glucose + oxygen carbon + water + energy dioxide C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ATP exergonic Autotrophs making energy & organic molecules from light energy carbon dioxide + water + energy glucose + oxygen 6CO 2 + 6H 2 O + light C 6 H 12 O 6 6O energy + 2 endergonic

4 Plant structure Obtaining raw materials u sunlight leaves = solar collectors u CO 2 stomates = gas exchange u H 2 O uptake from roots u Nutrients N, P, K, S, Mg, Fe uptake from roots

5 Chloroplast structure Double membrane Thylakoids Grana (stacks) Stroma (surrounds thylakoids) Chlorophyll & ETC in thylakoid membrane u H + gradient built up within thylakoids H +H+ H + H + H + H + H+ H + H +H+ H +

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

7 Photosynthesis Light reactions u convert solar energy to chemical energy ATP & NADPH Calvin cycle u sugar production reactions Uses (ATP & NADPH) to reduce CO 2 & synthesize C 6 H 12 O 6

8 Photosystems The light-gathering antenna complexes Photosystem II Photosystem I Special chlorophyll a molecules that absorb best at different pigments: P680 & P700

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

10 Linear Electron Flow Noncyclic photophosphorylation PS II generates energy as ATP PS I generates energy as NADPH

11 Light Reaction con t Electron Transport Chain u Pumps H+ s to maintain gradient u NADP+ final e- acceptor in chain = NADPH Chemiosmosis to generate ATP u Diffusion of H + s down gradient into Stroma

12 Comparing Chemiosmosis

13 Light Reaction of Photosynthesis Photosystem II Photosystem I Video Video

14 Cyclic Electron Flow Cyclic Photophosphorylation If PS I can t pass electron to NADP, it cycles back makes more ATP, but no NADPH No oxygen is released First type of photosynthesis Ex: Bacteria with one photosystem

15 Moving on to Calvin cycle Location: stroma Uses products of light reactions to drive synthesis reactions u ATP u NADPH

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

17 Calvin cycle (3 CO 2 enter one at a time) 3. Regeneration of RuBP PGAL to make glucose 3 ATP 3 ADP ribulose bisphosphate RuBP 5C 1C CO 2 Rubisco -enzyme that Binds CO 2 to RuBP 6C 1. Carbon fixation sucrose cellulose etc. PGAL 3C x2 2x 3C PGA 6 NADPH 6 NADP 2. Reduction 2x 3C 6 ATP 6 ADP

18 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! u can be used to make: Glucose, sucrose, lipids, amino acids etc.

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

20 Factors that affect Photosynthesis Enzymes are responsible for several photosynthetic processes, therefore, temperature and ph can affect the rate of photosynthesis. The amount and type of light can affect the rate. A shortage of any of the reactants,co2 and/or H2O, can affect the rate.

21 Energy Cycle sun Photosynthesis CO 2 H 2 O glucose O 2 Cellular Respiration ATP

22 Summary of photosynthesis 6CO 2 + 6H 2 O + light C 6 H 12 O 6 6O energy + 2 Where did the CO 2 come from? Where did the CO 2 go? Where did the H 2 O come from? Where did the H 2 O go? Where did the energy come from? What s the energy used for? What will the C 6 H 12 O 6 be used for? Where did the O 2 come from? Where will the O 2 go? What else is involved that is not listed in this equation?