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

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 –CO 2 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 O 2 to make a 2 carbon molecule which the mitochondria and perioxisomes can change to CO 2 This produces not ATP or food Uses Calvin cycle products Seems useless but probably left over from day when there was more CO 2 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 CO 2 more easily than rubisco When CO 2 levels are low, this can change CO 2 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 CO 2 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 CO 2