Photosynthesis 1 Flashcards
Pigment
any substance that absorbs light
energy
The color that something is, is what it reflects
Chloroplast pigments:
Chlorophyll
Carotenoids
Chlorophyll
green (reflect green)
* Absorb in red, violet, and blue regions of spectrum
Carotenoids
red, orange, yellow
A)carotenes: red, orange, yellow
B)xanthophylls: pale yellow
Action Spectrum for Photosynthesis
-Shows the relative effectiveness of different
wavelengths of light in promoting photosynthesis
Absorption Spectrum of a pigment shows
the
wavelengths of light that are absorbed by a
pigment.
If one compares the Action Spectrum of a
process with Absorption Spectra, one can get
an idea of
what pigments play a role in the
process.
When one compares
the action spectrum for
photosynthesis with the
absorption spectra for
chlorophylls a and b and
for carotenoids
they
overlap supporting that
chlorophylls and
carotenoids absorb light
for photosynthesis.
When isolated chlorophyll (no longer in chloroplasts) absorbs
light,
the energy levels of electrons are elevated.
– These electrons are said to be in an excited state.
– The excited electrons drop back to the ground state, and
energy is released as fluorescence; and some
energy is lost as heat
light=
fluorescence
When chlorophyll absorbs light energy while in chloroplast
membranes or other photosynthetic membranes:
– The excited electrons do not drop back down to the
ground state, but are transferred to electron carriers.
– The energy is trapped and stored in chemical bonds
Adenosine triphosphate (ATP) =
Energy
currency of cell.
Plants make ATP using
light as an energy
source.
Photosynthesis Takes place in
membranes of chloroplasts or
in membranes of photosynthetic prokaryotic
organisms
where does the Light-Dependent Reactions happen in
thylakoid membranes of chloroplasts
step 1 of Light-Dependent Reactions
Water molecules split apart, releasing electrons and
hydrogen ions; oxygen gas released.
step 2 of light dependent reactions
Electrons pass to electron carriers of electron
transport system.
step 3 of light dependent reactions
NADP (nicotinamide adenine dinucleotide
phosphate) is reduced, forming NADPH (reduced
nicotinamide adenine dinucleotide phosphate)
– used in light-independent reactions
Hydrogen ions play major role in
ATP production
Light-Independent Reactions happens where specifically in the chloroplast
In stroma of chloroplasts
Calvin cycle step 1
Carbon dioxide combines with RuBP (ribulose
bisphosphate)
what drives calvin cycle
– ATP and NADPH from light-dependent reactions
provide energy to drive Calvin cycle
Calvin cycle step 2
– The energy from ATP and NADPH becomes trapped
in chemical bonds of carbohydrates that are
produced
Two types of photosynthetic units:
Photosystem I and Photosystem II
Photosystem I (PS I)
antenna pigments
– About 200 molecules of chlorophyll a (blue-green)
– Some chlorophyll b (yellow-green)
– Carotenoids
Photosystem I (PS I) reaction center
P700
P700
Pigment at 700 nm: a special type of chlorophyll with an absorption peak at 700 nm
– The only chlorophyll in PS I that can use the trapped light energy
Photosystem II (PS II)
Antenna pigments and reaction center
(chlorophyll a & b; and carotenoids)
p680
Oxygen Evolving Complex (OEC)
sites where water is split
When something is reduced
it gains an electron or
electrons and sometimes protons (hydrogen atoms)
When something is oxidized
it gives up an electron or
electrons and sometimes protons (hydrogen atoms)
Oxidation of one compound usually coupled with
reduction of another compound
Photosystem l step 1
Antenna pigments absorb and pass light energy to reaction center P700
photosystem 1 step 2
Light energy absorbed by P700 boosts electrons to higher energy levels.
photosystem 1 step 3
Electrons passed in a series of oxidation-reduction reactions, to iron-sulfur acceptor
molecule Fe-S, then to ferredoxin, then to FAD (flavin adenine dinucleotide).
* NADP reduced to NADPH.
photosystem 1 step 4
Now there is an electron gap in PS I.
* Electrons removed from P700 replaced by electrons from Photosystem II.
photosystem 2 step 1
Antenna pigments absorb and pass light energy to P680 at the
reaction center
– Light energy absorbed by P680 boosts electrons to higher
energy levels.
photosystem 2 step 2
Electrons are passed to the acceptor molecule pheophytin, then
to PQ (plastoquinone), then along electron transport system in a
series of oxidation-reduction reactions to photosystem I
Photolysis
Water-splitting,occurs at the Oxygen Evolving
Complex (OEC) at Photosystem II
step 3 of photosystem 2
Photolysis
Electrons extracted from water replace electrons lost by P680.
what is produced from photosystem 2
One molecule of oxygen, 4 protons and 4 electrons produced
from two water molecules.
Chemiosmosis step 1
Protons build up in thylakoid space
due to splitting of water molecules
and as a result of protons being
ferried across membrane during
oxidation-reduction reactions of
electron transport.
chemiosmosis step 2
Proton gradient results in proton
motive force (like stored energy in a
battery). The only way protons can
leave the thylakoid space is through
special ATPases in thylakoid
membrane
chemiosmosis step 3 Movement of protons across
membrane =
source of energy for
synthesis of ATP
https
André Jagendorf
Jagendorf conducted
the experiments that
showed that
chemiosmosis occurs in
chloroplasts
Peter Mitchell had
determined the
chemiosmosis results in
ATP synthesis in
mitochondria.
sucrose
transport form of carbohydrate in plants
a disaccharide=
1 glucose+1 fructose
starch
storage carbohydrate in plants (monomer=glucose)
Inputs of the
Light Reactions
light
water
Products of the
Light Reactions
- ATP
- NADPH
- Oxygen from the splitting of
water
