1. Chapter 10:
Photosynthesis

2. Photosynthesis in nature
Autotrophs:
Producers
Make organic food from inorganics
Photoautotrophs
Chemoautotrophs
Heterotrophs:
Consumers
Get organic food by eating organisms or their by- products (decomposers)

4. The chloroplast Photosynthesis site Pigment: chlorophyll
Plant cell: mesophyll
Gas exchange: stomata
Double membrane
Thylakoids, grana, stroma

5. Photosynthesis: an overview
Redox process
H2O split (Photolysis)
e- (w/ H+) given to CO2, reduces it to sugar
2 major steps:
Light reactions (“photo”)
NADP+ (electron acceptor) --> NADPH
Photophosphorylation: ADP + P ---> ATP
Calvin cycle (“synthesis”)
Carbon fixation: carbon into organics

6. BioFlix: Photosynthesis

7. Photosystems Light harvesting units of thylakoid membrane
Composed mainly of protein/antenna pigments
Antenna pigment molecules struck by photons
Energy passes to rxn centers
Excited e- from chlorophyll is trapped by a primary e- acceptor
Used e- replaced by 1 from photolysis

8. RESULTS Fig. 10-9 Chloro- Chlorophyll b Absorption of light by
phyll a
Chlorophyll b
Absorption of light by
chloroplast pigments
Carotenoids
(a) Absorption spectra
400
500
600
700
Wavelength of light (nm)
(measured by O2 release)
Rate of photosynthesis
Figure 10.9 Which wavelengths of light are most effective in driving photosynthesis?
(b) Action spectrum
Aerobic bacteria
Filament
of alga
(c) Engelmann’s
experiment
400
500
600
700

9. Animation: Light and Pigments

10. Noncyclic electron flow
Photosystem II (P680):
1st photosystem
photons excite chlorophyll e- to an acceptor
e- replaced by splitting H2O
release of O2
e-s fall down ETC to PSI
as e- fall, ADP ---> ATP
noncyclic photophosphorylation

11. Noncyclic electron flow cont.
Photosystem I (P700):
‘fallen’ e- replace excited e- to primary e- acceptor
2nd ETC transfers e- to NADP+ ---> NADPH (...to Calvin cycle…)
Equal amounts of ATP and NADPH produced

13. Cyclic electron flow Alternative cycle (due to low ATP)
ONLY PS I used (not II)
Produces ATP only
Why?
Calvin cycle uses more ATP than NADPH
Cyclic photophosphorylation

15. The Calvin cycle 3 molecules CO2 are ‘fixed’ into 1 G3P Phases:
Carbon fixation
CO2 attached to each RuBP (rubisco enzyme)
Reduction
E-s from NADPH reduce 6C to G3P, ATP used
Regeneration
G3P rearranged to RuBP , ATP used, cycle cont.

17. Calvin Cycle, net synthesis
For each G3P (and for 3 CO2)…….
Consumption of 9 ATP’s & 6 NADPH
light rxns regenerate these
G3P used by plant to make glucose & other organic compounds

18. A review of photosynthesis

19. You should now be able to:
Describe the structure of a chloroplast
Describe the relationship between an action spectrum and an absorption spectrum
Trace the movement of electrons in linear electron flow
Trace the movement of electrons in cyclic electron flow
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

20. Describe the role of ATP and NADPH in the Calvin cycle
Describe the similarities and differences between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts
Describe the role of ATP and NADPH in the Calvin cycle
Describe the major consequences of photorespiration
Describe two important photosynthetic adaptations that minimize photorespiration
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings