Transcript Photosynthesis – Part II

Photosynthesis – Part II
Spring 2013 - Althoff Reference: Mader & Windelspecht Ch. 7)
• Plants as
Solar
Energy
Converters
• Plants as
Carbon
Dioxide
Fixers
Lec
08
Solar Energy & Wavelengths
• There are 7 basic categories of radiant (aka solar)
energy in the electromagnetic spectrum:
gamma rays
x-rays
UV
___________________
infrared
microwaves
radiowaves
• Visible spectrum: 380-750 nm (nanometers)
Visible Light
• Wavelengths different for ______________
Increasing wavelength
Increasing ENERGY
Absorption Spectrum for __________________
Pigments
chlorophyll a
chlorophyll b
carotenoids
For the record…
• Notice that the different photosynthetic pigments
have different absorption spectrums
• Chlorophyll a and b have a wider “_________” range
than carotenoids….as carotenoids do not have any
absorption beyond approximately 500 nm.
• Because of the wider absorption spectrum,
chlorophyll a and b play “THE” ____________ roles
in photosynthesis…
• Carotenoids play an _____________ role.
Non-cyclic
pathway
Electron flow
in light reactions
3
2a
2
3a
4
1
4
4a
Electron Flow…starting with the light reactions
• ______________________– the route electrons
usually travel during the ___________________.
1
2
• Starts with “Photosystem II” (although it happens
essentially first).
• Pigments absorb solar energy, then pass to other
pigments until it is concentrated in a particular pair
of ____________________ molecules—known as
the “______________________”
• Electrons (e-) become so energized that they escape
the reaction center and move to nearby _________
_________________
Electron Flow…from light reaction to Calvin
cycle reactions…
• Water splits, releasing ____ into the atmosphere
3
4
• The H+ stays in the ________________ and
contribute to the formation of the H+ gradient.
• Electron acceptor sends __________ electrons down
an electron transport chain.
• Combined with ATP synthase complexes, ATP
production occurs…which is then….
• Used by the ______________________ in the
_________ to reduce CO2 to a carbohydrate
simultaneously on the Calvin cycle reactions side…
2a
3a
4a
• Energized electrons leave the reaction center, to the
electron receptor…
• to merge with NADP+ and H+ to form ________. This
is on the ____________________ side…2 electrons
are accepted here.
• In the Calvin cycle reactions, the NADPH along with
the ATP that came from the light reaction side
_________ CO2 to CH2O (aka a carbohydrate)
Organization of the Thylakoid Membrane
• Photosynthesis II – pigment
complex and electronacceptor molecules; releases
O2
• Electron transport chain
carries electrons from PS II to
PS I via _______________. H+
• ________________
pumped from stroma into
complex is an
thylakoid space.
enzyme that joins
• Photosynthesis I – pigment
ADP + P to make ATP
complex and electron
acceptor molecules reduces
NADP+ to NADPH
ATP Production
• Thylakoid space acts as a ____________ for many H+.
• As water is _____________, two H+ remain in the
thylakoid space.
• Result: __________ in thylakoid space than in the
stroma…then flow of H + to from _____________
concentration provides kinetic energy that allows ATP
synthase complex enzyme to join ADP + P. This
method of producing ATP is called chemiosmosis—
what we looked before (Chapter 6)
• Summarized in next slide 
PS II
PS I
chemiosmosis
Plants as Carbon Dioxide Fixers
• Calvin cycle discovered by ______________ and
colleagues, used radioactive isotope 14C as a tracer to
“follow around” the reactions.
• Photosynthesis uses CO2 from the ______________ to
produce carbohydrates.
• Question…how does the CO2 get into atmosphere in
the first place??? Answer: when ____________ take
in O2 they ______ CO2. Of course, the CO2 is
produced by cellular respiration (the details starting after
the next exam).
• Carbon dioxide (CO2) fixation is the first step of the
Calvin cycle. As shown in the next slide 
________________
Reactions – details
these ATP & NADPH
produced by
light reactions
1
2
these ATP
produced by
light reactions
3
The Calvin cycle reactions
1
2
• ___________– 1st step – molecule of carbon dioxide
from atmosphere is attached to _____ (ribulose-1, 5bisphosphate), a 5-carbon molecule. The result is a
6-carbon molecule, which splits into two __________
__________. Enzyme that speeds up this reaction is
RuBP carboxylase—a protein that makes up 20-50%
of the content of chloroplasts. Large amount
necessary because, compared to other enzymes it is
rather slow acting.
• ______________– 2nd step – first 3-carbon molecule
is called 3PG (3-phosphoglycerate). Each of 2 3PG
molecules undergoes reduction to make ____
(glyceraldehyde-3-phosphate)—in 2 steps
The Calvin cycle reactions…con’t
3
• _________________ – 3rd step – in diagram on
previous slide, notice Calvin cycle reactions are
multiplied by 3 because it takes three turns of the
Calvin cycle to allow one G3P to exit….
• Results in 5 molecules of GCP per every 3 turns to
reform 3 molecules of RuBP…and the cycle continues.
• The reaction uses some of the ATP produced from
light reactions.
Importance of the Calvin cycle
• _____ is a product of the Calvin cycle – it can be
converted to other molecules the plant needs
• ____________________ is among the organic
molecules that result from GCP metabolism
• This is of interest because glucose is “the” molecule
that plants and animals most often _____________
to produce ATP molecules required to meet their
energy needs.
• Examine next slide to see the _______ of G3P.
Fate of G3P
Glucose phosphate
Fatty acid
synthesis
Amino acid
synthesis
Starch
(in roots and seeds)
Cellulose
(in trunks, roots
and branches)
+
Fructose phosphate
+
Sucrose
(in leaves,
fruits and seeds)