AP Biology
Photosynthesis: Life from Light
AP Biology
Energy needs of life All life needs a constant input of energy
Heterotrophs get their energy from “eating others” consumers of other organisms consume organic molecules
Autotrophs get their energy from “self” get their energy from sunlight use light energy to synthesize organic
molecules
AP Biology 2005-2006
How are they connected?
glucose + oxygen carbon + water + energydioxide
C6H12O6 6O2 6CO2 6H2O ATP+ + +
Heterotrophs
+ water + energy glucose + oxygencarbondioxide
6CO2 6H2O C6H12O6 6O2light
energy + ++
Autotrophsmaking energy & organic molecules from light energy
making energy & organic molecules from ingesting organic molecules
AP Biology
Energy cycle
Photosynthesis
Cellular Respiration
glucose O2H2OCO2
ATP
sun
The Great Circleof Life!
Where’s Mufasa?
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What does it mean to be a plant Need to…
collect light energy transform it into chemical energy
store light energy in a stable form to be moved around the plant
& also saved for a rainy day need to get building block atoms from
the environment C,H,O,N,P,S
produce all organic molecules needed for growth carbohydrates, proteins, lipids, nucleic acids
AP Biology 2005-2006
Plant structure Obtaining raw materials
sunlight leaves = solar collectors
CO2
stomates = gas exchange regulation
Found under leaves
H2O uptake from roots
nutrients uptake from roots
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Chloroplasts double membrane stroma thylakoid sacs grana stacks
Chlorophyll & ETC in thylakoid membrane H+ gradient built up
within thylakoid sac
Plant structure
H+ H+
H+
H+
H+H+
H+ H+
H+H+
H+
AP Biology 2005-2006
Pigments of photosynthesis
chlorophyll & accessory pigments “photosystem” embedded in thylakoid
membrane structure function
Why does this structure make sense?
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Light: absorption spectra Photosynthesis performs work only with
absorbed wavelengths of light chlorophyll a — the dominant pigment —
absorbs best in red & blue wavelengths & least in green
other pigments with different structures have different absorption spectra
AP Biology
Photosystems Photosystems
collections of chlorophyll molecules
2 photosystems in thylakoid membrane act as light-gathering “antenna complex” Photosystem II
chlorophyll a P680 = absorbs 680nm
wavelength red light Photosystem I
chlorophyll b P700 = absorbs 700nm
wavelength red light
AP Biology
Transfer of Electrons in PSII & PSI In both PSII and PSI, the energy from the
excited e- pumps H+ into the thylakoid as it moves through the ETC.
Electrons from PSII are transferred to PSI. After electrons have moved through PSI,
an intermediary molecule (embedded in the membrane and adjacent to PSI) transfers the e- to NADP+. A H+ is attracted to this molecule and NADPH is formed.
AP Biology 2005-2006
Chemiosmosis in Photosynthesis**(similar in Cell Respiration)
proton (H+) gradient across inner membrane
drive ATP formation ATP synthase
enzyme
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Summary of the LDR PS II absorbs light
excited electron passes from chlorophyll to “primary electron acceptor” at the REACTION CENTER. splits H2O (Photolysis!!) O2 released to atmosphere
PS I absorbs light Produces NADPH (stored energy) which will be
used by the Calvin cycle Chemiosmosis produces ATP from light
energy ATP will be used by the Calvin Cycle
AP Biology
ETC of Photosynthesis Chloroplasts transform light
energy into chemical energy of ATP
use electron carrier NADPH
split H2O
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2 Photosystems Light reactions
elevate electrons in 2 steps (PS II & PS I) PS II helps generate
energy as ATP (H+ pumps)
PS I generates reducing power as NADPH
This shows Noncyclic photophosphorylation.
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ETC of Photosynthesis
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ETC of Photosynthesis
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Cyclic photophosphorylation If PS I can’t pass
electron to NADP, it cycles back to PS II & makes more ATP, but no NADPH coordinates light
reactions to Calvin cycle
Calvin cycle uses more ATP than NADPH
AP Biology
Do Now: Light Reactions Summary Questions
Where did the energy come from?Where did the H2O come from?Where did the electrons come from?Where did the O2 come from?Where did the H+ come from?Where did the ATP come from?Where did the O2 go?What will the ATP be used for?What will the NADPH be used for?
AP Biology
Calvin Cycle Overview Calvin cycle
uses chemical energy
(NADPH & ATP)
to reduce CO2 to
build C6H12O6 (sugars)
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From Light reactions to Calvin cycle Calvin cycle
Occurs in the stroma of the chloroplast
Need products of light reactions to drive synthesis reactions ATP NADPH
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From CO2 C6H12O6
CO2 has very little chemical energy fully oxidized
C6H12O6 contains a lot of chemical energy reduced endergonic
Reduction of CO2 C6H12O6 proceeds in many small uphill steps each catalyzed by specific enzyme using energy stored in ATP & NADPH
AP Biology
PGALto make glucose
6Cunstable
intermediate
1C CO2
Calvin cycle
5CRuBP
3C2xPGA
6 ADP
6 ATP
3C2x
3C x2PGAL
6 NADP
6 NADPH
3 ADP
3 ATPRubisco
1. Carbon fixation
2. Reduction
3. Regeneration
ribulose bisphosphate
ribulose bisphosphatecarboxylase
sucrosecellulose
etc.
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Rubisco Enzyme which fixes carbon from
atmosphere ribulose bisphosphate carboxylase the most important enzyme in the world!
it makes life out of air! definitely the most abundant enzyme
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Calvin cycle PGAL
end product of Calvin cycle energy rich sugar 3 carbon compound “C3 photosynthesis”
PGAL important intermediatePGAL glucose carbohydrates
lipids
amino acids
nucleic acids
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Photosynthesis summary Light reactions
produced ATP produced NADPH consumed H2O produced O2 as byproduct
Calvin cycle consumed CO2
produced PGAL regenerated ADP regenerated NADP
AP Biology 2005-2006
Summary of photosynthesis
Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the H2O go? Where did the energy come from? What’s the energy used for? What will the C6H12O6 be used for? Where did the O2 come from? Where will the O2 go? What else is involved that is not listed in this
equation?
6CO2 6H2O C6H12O6 6O2light
energy + ++
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