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Photosynthesis 6CO 2 + 12H 2 0 C 6 H 12 O 6 + 6O 2 + 6 H 2 O.

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Presentation on theme: "Photosynthesis 6CO 2 + 12H 2 0 C 6 H 12 O 6 + 6O 2 + 6 H 2 O."— Presentation transcript:

1 Photosynthesis 6CO H 2 0 C 6 H 12 O 6 + 6O H 2 O

2 Overview Light-dependent reactions of photosynthesis Light-independent reactions of photosynthesis C3 versus C4 metabolism Write an essay on the light-dependent (light) reactions of photosynthesis Write an essay on the light-independent (Dark) reactions of photosynthesis Compare and contrast C3 and C4 metabolism

3 Photosynthesis Light reactions Calvin/Benson Cycle (Dark Reactions) ADP ATP NADP+ NADPH CO 2 Sucrose H 2 O O 2

4 Photosynthesis occurs only in the chloroplasts Vacuole Palisade cell Stroma Chloroplast Thylakoids Thylakoid space Grana PSII PSI

5 The light reactions of photosynthesis

6 Plants absorb Light Wavelength of light (nm) GreenRed Blue Abs Chlorophyll a Chlorophyll b Carotenoids

7 Absorption of light leads to excited electrons When light energy is absorbed by chlorophyll, an electron is promoted to a higher (more energetic) orbital. This energy can be lost by: –from one orbital to the next with loss of heat –back to the ground state with loss of light (fluorescence) and heat –transfer to another chlorophyll.

8 Chlorophylls are organised into photosystems to trap light energy Light Chlorophylls are organised into photosystems Transfer of light energy from one chlorophyll to another Special chlorophyll molecule - primary electron acceptor

9 Cyclic photosphorylation generates ATP PQ PSIIPSI Stromal side Thylakoid space side Fd P700

10 Non-Cyclic photosphorylation generates ATP and NADPH PQ PSII PSI Stromal side Thylakoid space side Fd NADP+ NADPH Q P700P680 H 2 0 2H+ & 2e- & 1/2 O 2

11 Generation of ATP H+ gradient generated by: –PQ shuttle (H+) –Splitting of water (2H+) –NADPH production (2H+ removed from stroma) ATP generated by an ATP synthase as H+ ions flow through it ADP +Pi ATP H+ Stroma

12 Light-independent reactions

13 The Calvin/Benson cycle Ribulose biphosphate CO 2 Carbon Phosphorus 3-phosphoglycerate ATP ADP 1,3 diphospho- glycerate NADPH NADP+ Glyeraldehyde-3-phosphate G-3-P Sugars ATP ADP

14 C4 metabolism

15 C3 and C4 metabolism Inefficient as RUBISCO can act as both a carboxylase and as an oxygenase. Oxygenase activity leads to loss of carbon that has already been fixed. Some plants have an alternative pathway where CO 2 is first fixed into C4 organic acids (C4 pathway) and then liberated later to undergo the Calvin/Benson cycle (C3 metabolism).

16 C4 metabolism 2 types C3 and C4 metabolism are separated in space (different cells) e.g. sugar cane Characteristic aggregation of cells around the vascular bundles - Krantz morphology C3 and C4 metabolism are separated in time (same cell) e.g. pineapple.

17 Comparison of C3 & C4 leaves C3 - note the lack of chloroplasts in the bundle sheath C4 - note the extensive chloroplasts in the bundle sheath

18 Separation in space Vascular tissue Bundle sheath cell Mesophyll cell surrounding bundle sheath CO 2 PEP (3C) C3 CO 2 OAA (4C) Pyruvate (C3) ATP ADP sugar


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