AP Biology 2

Notes Chapter 10

Photosynthesis

Introductory Vocab

• 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

• Wavelength

• ROYGBIV

• Photons

• Beneficial for photosynthesis

• Reflection and absorption in plants

• Spectrophotometer

Chlorophyll

• 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