Download Photosynthesis Notes

Chapter 9
Energy in the Cell
ATP
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Adenosine triphosphate
Quick source of energy
Does not last long
The energy is stored in the bonds between
the phosphates
Structure of the Chloroplast
Chloroplast
• Contains pigments
– Molecules that absorb light of a specific
wavelength
– Chlorophyll – most common – absorbs
most wavelengths EXCEPT green
– Carotenoid – red, orange, yellow
• Carotenes
• Xanthophylls
Photosynthesis
• Process that captures the sun’s energy and
transforms it into simple sugars
• 6CO2 + 6H2O  C6H12O6 + 6O2
• Occurs in the chloroplast
• Two phases:
– Light dependent – occurs in the membrane of
the thylakoid – makes ATP
– Light independent – occurs in the stoma of the
chloroplast - makes simple sugars
Light Dependent Reactions
• Requires sunlight
• E from the light is transferred to e• These excited e- enter the e- transport chain of
photosystem II
– Photosystem – a series of proteins embedded in the
membrane of the thylakoid
Photosystem II and I
• P II – e- is passed down the e- transport
chain – makes ATP or pumps H+ into the
center of the thylakoid disc at each step
• P I – re-energized e- is passed down a
second e- transport chain
– @ the end, the e- is transferred to NADP
– Forms NADPH which is used in the lightindependent reactions
– NADP is a carrier – it just transports the e- (like
a taxi)
The e- Taken From the
Chlorophyll Must be Replaced!
• In PII water is split: photolysis
– Creates oxygen, H+, and e– Oxygen – released
– H+ - pumped into the thylakoid to create a
concentration gradient
– e- returned to the chlorophyll
What happens to the H+?
• An enzyme ATP synthetase allows the H to
move down the concentration gradient and
makes ATP
Light-Independent Reactions
• Calvin Cycle (C3)
• Make sugar from CO2
– Carbon fixation
• Occurs in the stroma of the chloroplast
C4 and CAM
• Used by plants in dry climates.
• In dry climates, the stomata (pores) in the
leaves need to stay closed to prevent water
loss. This causes the CO2 levels to drop.
• If not enough CO2 is available C3 plants
will begin grabbing O2 and burning sugars
instead of making them (photorespiration)
• The protein in the light-independent rxn is
more efficient at grabbing CO2