Photosynthesis 1 Flashcards by shweta rajam

Pigment

any substance that absorbs light
energy

The color that something is, is what it reflects

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Chloroplast pigments:

Chlorophyll
Carotenoids

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Chlorophyll

green (reflect green)
* Absorb in red, violet, and blue regions of spectrum

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Carotenoids

red, orange, yellow
A)carotenes: red, orange, yellow
B)xanthophylls: pale yellow

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Action Spectrum for Photosynthesis

-Shows the relative effectiveness of different
wavelengths of light in promoting photosynthesis

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Absorption Spectrum of a pigment shows

the
wavelengths of light that are absorbed by a
pigment.

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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.

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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.

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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

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light=

fluorescence

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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

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Adenosine triphosphate (ATP) =

Energy
currency of cell.

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Plants make ATP using

light as an energy
source.

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Photosynthesis Takes place in

membranes of chloroplasts or
in membranes of photosynthetic prokaryotic
organisms

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where does the Light-Dependent Reactions happen in

thylakoid membranes of chloroplasts

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step 1 of Light-Dependent Reactions

Water molecules split apart, releasing electrons and
hydrogen ions; oxygen gas released.

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step 2 of light dependent reactions

Electrons pass to electron carriers of electron
transport system.

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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

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Hydrogen ions play major role in

ATP production

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Light-Independent Reactions happens where specifically in the chloroplast

In stroma of chloroplasts

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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

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