Photosynthesis and Plants

6CO2 + 6H2O + sunlight C6H12O6 + 6O2

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

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

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

C4 photosynthesis

CAM photosynthesis