in this figure are Curve 1= bacteriochlorophyll a, Curve 2=chlorophyll a, Curve 3=chlorophyll b, Curve
4=phycoerythrobilin, Curve 5=B carotene.
•Fig 7.8 Absorption spectra compared w/ action spectra
Absorption spectra: effectiveness of chlorophyll molecule to absorb different light .
Action spectra: effectiveness of different light to drive some biological process (here it is O2
-There is a very close match btw absorption and action spectra. To measure O2 concentration, light
was shined onto the alga (spirogyra)’s chloroplast. Aerotactic bacteria aggregated at ↑O2 regions
(in spectrum region where chlorophyll absorbed most effectively Blue, Red). It was first
indication of effectiveness of light absorbed by accessory pigments in driving photosynthesis.
•Fig 7.11 Relationship of oxygen production to flash energy
Chlorella- short light flashes of different intensity, O2 release was measured, O2 release saturated
at high intensity.
They thought that 1chlorophyll would yield 1 O2. However, the finding was that 2500 chlorophyll
molecules would release 1 O2 at saturating energies. This was done by quantifying chlorophyll
amount and O2 amount and forming a ratio.
•Reasons for 1 O2/2500 chlorophylls:
1.Hundreds of chlorophylls absorb light and transfer energy via resonance transfer until it’s all
funneled to 1 chlorophyll molecule (reaction center). Electron transfer then happens.
2.Each reaction center needs to operate 4 times to generate 1 O2.
3.2 different types of reaction centers (photosystems) working in series
•Fig 7.10 Basic concept of energy transfer during photosynthesis
2 stages: (1) Physical transfer: many chlorophyll pigments collect light and transfer it via
resonance transfer to reaction center. (2) chemical reactions store some of energy in reaction center
by transferring e- to an acceptor mol. An e- donor then reduces the chlorophyll reaction center
•A. Red drop effect not consistent w/ findings.
Quantum yield = # of photochemical produces / total # of quanta absorbed
Far red light (> 680nm) is inefficient at driving photosynthesis.
Quantum yield of O2 evolution falls off drastically for far-red light of wavelengths > 680n meaning
that red light alone isn’t enough at driving photosynthesis. The dip near 500nm reflects the lower
efficiency of photosynthesis using light absorbed by accessory pigments (carotenoids).
•B. Emerson enhancement effect: the rate of photosynthesis when red and far-red light are given
together is greater than the sum of the rates when they are given apart.
The enhancement effect provided proof that photosynthesis is carried out by 2 photochemical systems
working in tandem but slightly different optima.
•2 photosystems working in series : 2 physically and chemically different, each w/ own chlorophyll
antenna pigments and reaction center. Both are liked by electron transport chain.
PS II ≈690nm absorption maxima, poor absorption of far red (P680 reaction center), in grana
PS I ≈700nm absorption maxima (P700 reaction center), in stroma lamellae
•The “Z scheme” (zig zag scheme)
Red light is absorbed by PSII producing strong oxidant and weak reductant.
Far red light is absorbed by PSI and produces strong reductant and weak oxidant.
The strong oxidant generated by PSII oxidizes water while the strong reductant produced by PSI
The reductant produced by PSII re-reduces oxidant produced by PSI.
•Fig 7.16 Schematic picture of overall organization of chloroplast membranes
Chloroplast is surrounded by inner and outer membranes (envelopes, lipid bilayer).