Photosynthesis and Plants  6CO 2 + 6H 2 O + sunlight C 6 H 12 O 6 + 6O 2  Epidermis with cuticle  palisade mesophyll – parenchymal cells – primary sites of photosynthesis  Spongy mesophyll – CO2 exchange  Vascular bundles – xylem and phloem for water and sugar transport  Lower epidermis with stomata and guard cells

Cross section of leaf

Chloroplast anatomy

Reactions of Photosynthesis  Light reactions  Dark reactions – Calvin cycle

Light Reaction  Photons strike thylakoid membrane activating chlorophyll and electrons from water  Excited electrons move down electron transport chain  ATP and NADPH are produced

Antenna complex  Chlorophyll a, b, and carotenoids  Pigments gather light  Reaction ctr. “excites” electrons  light reactions light reactions

Non-cyclic Photophosphorylation

Cyclic Photophosphorylation  Simple way to create ATP  Photons absorbed in PS I (700)  Electrons excited  Passed down cytochrome ETS  ATP generated, electrons passed back to PS I  No NADPH  No photolysis

Dark Reactions  Use ATP, CO2, and NADPH to create sugars  Calvin cycle Calvin cycle

Photorespiration  Rubisco starts to bind oxygen because CO2 availability is limited  C4 alternative – CO2 combines with PEP to form oxaloacetate (4 Carbon sugar)  PEP carboxylase (enzyme that catalyzes C4 rxn.) has high affinity for CO2.  Oxaloacetate converts to malate and shuttled to bundle sheath cells  CO2 released for use in Calvin cycle  CAM alternative is day/night cycle

C 4 photosynthesis

CAM photosynthesis