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Photosynthesis [Chapter 7]
Photosynthesis - Light Reactions
Light - hot vibrating dipole (solar) —> [hot relates to the colour temperature]
Frequency (f) = velocity / wavelength
Energy = hf
Wavelength max = [3
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K] / K
K= temperature in Kelvin scale
Absorption
Excitation

—> (both) Pigments

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Photosynthetic activity is thought about as terrestrial activity
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Light Reaction- How the process of photosynthesis takes light and converts it into
ATP
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We are an example of a black body- particular temperature and we emit photons
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2 things actually happen in changes of temperature
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Also get a shift
in the maximal wavelength where the maximum amount of photons are emitted
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Get hotter and hotter and shorter wavelength and
more photons emitted
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The sun is hot and thats the radiation
we are getting from the sun
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3000k - fairly warm lightreddish
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The
colour temperature of those bulbs will be about 4000k and that tells you the
relative difference in amounts of wavelengths being emitted
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High colour temperature is better because its closer to solar
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Colour temperature is basically the

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consequence of the wavelength being released by the black body radiant
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With regard to solar irradiance, most of the solar radiation is in the top in a part
that we can see [blue lines]
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[graph of solar irradiance]
Downward lines are points where light has been absorbed before reaching the sun
example hydrogen
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The pretty large downward lines are the clouds
or water vapour
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Underneath the atmosphere see a lot of absorption of the ultra violet light by
the ozone and then protects us from the damaging effects of the ultraviolet light
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When we think of that photosynthetic process have to think of the absorption and
the excitation of the photons that is being emitted by the sun
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Some of the light is
scattered but a lot of it will be absorbed by the pigments present in the leaf
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3 photosynthetic pigments
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The relationship is associated with the basic building block associated with
them
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The are four of them so tetra
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Made of the basic pyrrolle structure that is a cyclin
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Found usually in a
group of algae known as cyanobacteria or blue green algae
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Not absorbing in the
blue green region
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They also
synthesize a great number of toxins and contaminate cultures
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Based upon the pyrrolle and tetra cyclic pyrrolle linear structure
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There is a cyclic tetra pyrrolle
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One of the things that is interesting is that because it is cyclic instead of the
linear tetra pyrrolle
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They absorb in the
blue part of the spectrum as well as the red
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One other structure is the Carotenoids
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The three major pigments are a) phycobilins [ in archaea, old] b) chlorophyll —>
both rely on the tetra pyrrolle structure and c) Carotenoids
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Hemoglobin is also a tetra cyclic pyrrolle
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The cyclic or linear structures of tetra pyrolles or the double bonded structure of
Carotenoids all have the ability to form excitons
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Can also drop an energy level state when relaxation
occurs and then drops to the basal energy state which is when fluorescence
occurs [lower wavelength]
2 different energy states as seen above
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The excited
state is used in the production of ATP which then causes the reduction of NADPH
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In the chemical level, light is incorporated into chlorophyll which causes the
chlorophyll to get excited and can take an acceptor of an electron causing a
positively charged chlorophyll and can donate an electron to the acceptor which
now contains an electron through charge separation
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The negatively charged
acceptor is what does the chemical work associated with photosynthesis
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The above process is known as
the PS 2 photosystem
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Photosystem 2 is water splitting and photosystem 1 is NADP reduction
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—> non cyclic
phosphorylation
The third photosystem is the cytochrome b6 complex
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Positive charge on the chlorophyll is
extremely transient as a result of that
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Dark Reactions

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Occur in the light but don’t need light
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Carboxylation is
one
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The other part of
it is Cyclic regeneration to allow you to do this reduction of carbon dioxide over
and over again
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In the light reactions of photosynthesis, water molecules are split, oxygen is
liberated, and e’s that are released are used to reduce NADP+ —> NADPH
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During carbon-fixation reactions, the energy of ATP is used to link CO2 covalently
to an organic molecule, and the reducing power of NADPH is then used to reduce
the newly fixed carbon atoms to a simple sugar

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