AP Biology 2
Notes Chapter 10
Photosynthesis
Introductory Vocab
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Heterotrophs
Autotrophs
Chemoautotrophs
Mesophyll
Stroma
Grana
Thylakoids
PHOTOSYNTHESIS
• The equation:
– CO 2 + H 2 O  C H 2 O + O 2
• Light reactions (photo) occur in thylakoids
– Changes light energy to chemical energy
making NADP and ATP
• Calvin cycle (synthesis) occurs in the
stroma
– Uses the NADP and ATP to make sugar
Label the Parts
Light Review
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Wavelength
ROYGBIV
Photons
Beneficial for
photosynthesis
• Reflection and
absorption in plants
• Spectrophotometer
Chlorophyll
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Chlorophyll a
accessory pigments
Chlorophyll b
Carotenoids
Chlorophyll Molecule
Photosystems
• Chlorophyll is organized into photosystems
• These include an antenna complex, reaction
center chlorophyll and a primary electron
acceptor
• Photosystem I - contains chlorophyll a and
makes NADPH
• Photosystem II makes ATP
Converting light energy to
chemical energy
Light
Energy
Light
Energy
Electron Flow
• Non cyclic electron flow
– occurs in thylakoids and uses both
photosystems
– Passes electrons from water to NADPH
– Produces ATP and NADPH and oxygen by
splitting water
• Cyclic electron flow
– makes only ATP and uses Photosystem II
– This ATP will be used in the Calvin cycle
Chemiosmosis Differences
• MITOCHONDRIA
• Electrons come from
food
• Membranes pump
protons
• CHLOROPLAST
• Uses light energy
• Thylakoid membrane
pumps protons from
stroma to thylakoid
compartment and back
Light Reactions and
Chemiosmosis
Chemiosmosis Similarities
• Both mechanisms:
– work with ATP synthetase to produce ATP
from ADP
– have similar electron carriers
– ETC moves protons across a membrane down
an electromagnetic gradient
Calvin Cycle
• Similar to Krebs because the starting
material is regenerated
• Carbon enters as CO 2 and leaves as sugar
• Produces G3P
• Uses ATP
3 Phases of Calvin Cycle
• Carbon Fixation
– CO2 attaches to ribulose biophosphate (RuBP)
which is the starting material
– Rubisco is the enzyme that catalyzes this step
• Reduction
– Transfers a P from ATP to another molecule
– Removes electrons from NADPH
• Regeneration of RuBP
– Uses 3 ATP molecules to make 1 RuBp
Calvin Cycle Summary
• To produce one 6 carbon sugar (glucose) it
takes 18 ATP and 12 NADPH!
• The cycle must turn 6 times to make 1
glucose
Photorespiration
• Occurs on very hot dry days
• Occurs in C3 plants like rice, wheat and soybeans
• Rubisco can accept O2 to make a 2 carbon
molecule which the mitochondria and
perioxisomes can change to CO2
• This produces not ATP or food
• Uses Calvin cycle products
• Seems useless but probably left over from day
when there was more CO2 in air
• Reduces production of crops
C4 plants
• These include sugar cane
and corn
• Works in very hot, dry
regions
• This keeps the plant from
going through
photorespiration
• PEP carboxylase attaches
to CO2 more easily than
rubisco
• When CO2 levels are low,
this can change CO2 even
when rubisco cannot
CAM plants
• Cacti, pineapple
• Occurs in very dry regions
• These open the stomata only
at night to go through
photosynthesis…but no light!!
• Bring in CO2 during the night
and change to an organic
acids that is stored in the
vacuoles
• During light, organic acids are
released and changed back to
CO2