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Photosynthesis: Life from Light. 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 - PowerPoint PPT Presentation
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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?
AP Biology 2005-2006
Pigments of photosynthesis
chlorophyll & accessory pigments “photosystem” embedded in thylakoid
membrane structure function
Why does this structure make sense?
AP Biology
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
ETC of Photosynthesis ETC produces from light energy
ATP & NADPH NADPH (stored energy) goes to Calvin cycle
PS II absorbs light excited electron passes from chlorophyll to
“primary electron acceptor” at the REACTION CENTER. splits H2O (Photolysis!!) O2 released to atmosphere ATP is produced for later use
AP Biology 2005-2006
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
Photorespiration Why? When the stomates are closed
during hot-dry weather, the plant cannot get CO2 and Ribisco fixes O2 with RuBP.
2005-2006
AP Biology
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
AP Biology
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
AP Biology
C4 Plants Ex: grass and corn They have mesophyll cells (like C3
plants) but their chloroplasts are in Bundle-sheath cells.
Keep stomata closed most of the time b/c of hot weather to prevent water loss
Pep carboxylase fixes CO2 to produce a 4 carbon molecule in mesophyll cells
2005-2006
AP Biology
C4 plants 4-carbon compound moves to the
Bundle-sheath cells to make sugar. These plants only have PSI.
2005-2006
AP Biology 2005-2006
AP Biology
CAM (Crassulacean acid metabolism)
Ex: cacti and pineapples Close stomates during the day, open
them at night.
Take in CO2 during the night, but do not have ATP and NADPH. So incorporate the CO2 into a variety of organic acids.
During the day, CO2 is released from the acids to be used to make sugars.
2005-2006
AP Biology 2005-2006
Photosynthesis summary Light reactions
produced ATP produced NADPH consumed H2O produced O2 as byproduct
Calvin cycle consumed CO2
produced PGAL regenerated ADP regenerated NADP
