Absorption of light by chloroplast pigments RESULTS Chlorophyll

Absorption of light by chloroplast pigments RESULTS Chlorophyll a Carotenoids 400 (a) Absorption spectra Chlorophyll b 500 600 700 Wavelength of light (nm) (b) Action spectrum Rate of photosynthesis (measured by O 2 release) Fig. 10 -9 Aerobic bacteria Filament of alga (c) Engelmann’s experiment 400 500 600 700

Fig. 10 -10 CH 3 CHO in chlorophyll a in chlorophyll b Porphyrin ring: light-absorbing “head” of molecule; note magnesium atom at center Fig. 10 -17 Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown

Fig. 10 -17 STROMA (low H+ concentration) Cytochrome Photosystem I complex Light Photosystem II 4 H+ Light Fd NADP+ reductase H 2 O THYLAKOID SPACE (high H+ concentration) 1 e– Pc 2 1/ 2 NADP+ + H+ NADPH Pq e– 3 O 2 +2 H+ Fig. 10 -19 4 H+ To Calvin Cycle Thylakoid membrane STROMA (low H+ concentration) ATP synthase ADP + Pi ATP H+

Fig. 10 -19 The C 4 pathway C 4 leaf anatomy Mesophyll cell Photosynthetic cells of C 4 Bundleplant leaf sheath cell CO 2 PEP carboxylase PEP (3 C) ADP Oxaloacetate (4 C) Vein (vascular tissue) Malate (4 C) Stoma Fig. 10 -19 Bundlesheath cell ATP Pyruvate (3 C) CO 2 Calvin Cycle Sugar Vascular tissue

Fig. 10 -19 a C 4 leaf anatomy Mesophyll cell Photosynthetic cells of C 4 Bundleplant leaf sheath cell Fig. 10 -19 b Vein (vascular tissue) Stoma

Fig. 10 -19 b The C 4 pathway Mesophyll cell PEP carboxylase Oxaloacetate (4 C) PEP (3 C) ADP Malate (4 C) Bundlesheath cell CO 2 ATP Pyruvate (3 C) CO 2 Calvin Cycle Sugar Vascular tissue

Fig. 10 -20 Sugarcane Pineapple C 4 CAM CO 2 Mesophyll cell Organic acid Bundlesheath cell CO 2 1 CO 2 incorporated into four-carbon Organic acid organic acids (carbon fixation) CO 2 Calvin Cycle CO 2 2 Organic acids release CO 2 to Calvin cycle Night Day Calvin Cycle Sugar (a) Spatial separation of steps (b) Temporal separation of steps