HBio: Photosynthesis

Leaf Anatomy Cuticle – waxy coating to prevent desiccation Epidermis – outer layer of protective cells Vascular Bundle - vein Xylem – delivers water from roots Phloem – delivers sugars from leaves Mesophyll Palisade – tightly packed photosynthetic cells Spongy – loose arrangement of photosynthetic0 cells w/air spaces Stoma – openings allow for gas exchange Guard Cells – regulate stoma

Homework: Draw or describe the carbon cycle Explain how it relates to photosynthesis

Do Now: Homework on Desk Grab your clickers!

Which leaf structure is responsible for gas exchange? Epidermis Cuticle Mesophyll Guard cells Xylem Phloem

Which leaf structure is responsible for transport of water? Epidermis Cuticle Mesophyll Guard cells Xylem Phloem

Which leaf structure is responsible for synthesis of sugars? Epidermis Cuticle Mesophyll Guard cells Xylem Phloem

Which process increases C in the atmosphere? Reforestation Coal formation Burning fossil fuels

Chloroplasts Chloroplasts found in cells of mesophyll (interior tissue of leaf) CO2 enters and O2 exits through stomata (pores) Chlorophyll - green pigment absorbs light energy found in thylakoid membranes Thylakoids stacked in grana Stroma – fluid in chloroplast

Electromagnetic Spectrum

Spectrophotometer Measures the ability for a pigment to absorb various wavelengths of light Directs a beam of light of different wavelengths through a solution of the pigment and measures the fraction of the light transmitted at each wavelength Absorption spectrum plots a pigment’s light absorption vs. wavelength

ALL wavelengths are equally effective for photosynthesis True False Cannot be determined

The colors of light most useful in photosynthesis are green, yellow, and orange red, violet, and blue infrared, red, and yellow red, white, and blue

Big Picture: Energy Cycles All energy ultimately comes from sun Light reactions of photosynthesis Take place in thylakoid Carbon fixation -all C in living things ultimately from CO2 Dark reactions of photosynthesis Take place in stroma Photosynthesis and cellular respiration are reverse reactions

Redox Redox Rxns w/ transfer of e Oxidation – loss of e Reduction – gain of e Both photosynthesis and cellular respiration use redox rxns in a series of steps Electron transport chain (ETC) breaks the fall of electrons into several Energy releasing steps using proteins in the cell membrane

Photosystem Photosystem – reaction center surrounded by light harvesting complexes called pigments (chlorophyll a, chlorophyll b, xanthrophyll, carotenoids, etc) Pigment – absorbs photon E transferred from pigment to chlorophyll a rxn center Rxn Center – protein complex w/ primary e acceptor 2 photosystems used in light reactions Photosystem II – p680 chlorophyll a rxn center Photossystem I – p700 chlorophyll a rxn center

Light Reactions: Non-Cyclic e flow Photons absorbed by pigments and funneled to p680 in PSII excites e to higher energy state E is captured by primary e acceptor Enzyme splits H2O  2e + 2 H+ + O (will form O2) Excited e passes thru etc to rxn center in PSI Exergonic rxns in etc provide E for synthesis of ATP Photons excite e in p700 in PSI excites e to higher energy state E is captured by primary e acceptor and passed down 2nd etc NADP+ transfers 2e from etc to form NADPH

OR Light Reactions: Cyclic e flow Uses PSI only! (not PSII) Excited e from primary e acceptor to 1st etc produces ATP and e falls back to replace lost e from p700 No water splitting No production of NADPH Increases production of ATP for Calvin Cycle (req. more ATP then NADPH)

Chemiosmosis etc passes e thru carrier proteins in thylakoid membrane creating a H+ gradient (pumps H+ from stroma (pH8) into thylakoid space pH5) Chloroplasts – photophosphorylation ATP synthase embedded in same membrane (as H+ diffuse down gradient ADP is phosphorylated into ATP on stroma side of thylakoid) NADPH also made on stroma side of membrane

Classwork: Draw a flowchart (or diagram) of the light dependent reactions

Do Now Good Morning! Grab your Clicker Take out your photosyntehsis pogil Have out your homework ws (light reactions)

The light dependent reactions take place in the Cloroplast membrane Thylakoid Stroma Cytoplasm

NADP+  NADPH is an example of Reduction Oxidation Chemiosmosis Photophosphorylation None of the above

During what stage of photosynthesis is O2 produced? Photosystem I Photosystem II ETC Photophosphorylation O2 is not produced

The photophosphorylation of ATP is due to Chemiosmosis of H+ ATP synthase Electron Transport Chain All of the above None of the above

Dark Rxns: Calvin Cycle Anabolic rxns – consuming E to build sugar C enters Calvin cycle as CO2 C exits Calvin cycle as 3C sugar called G3P Uses ATP as E source (ATP) from light rxns Uses NADPH as reducing agent to add high E e (NADPH from light rxns) Phase I: Carbon Fixation CO2 + RuBP (5C sugar)  2 3- phosphoglycerate Phase II: Making Sugar Each 3-phosphoglycerate + P (from ATP)  1,3-biphosphoglycerate + 2e (from NADPH)  G3P Phase III: Regenerating RuBP (5) G3P + 3ATP  3 RuBP (ready for C fixation phase I) 3 molecules CO2  1 molecule G3P 6 molecules CO2  2 G3P (Glucose) Must go thru Calvin Cycle 6x to make 1 molecule of glucose!

Alternate Methods of C Fixation Hot/Dry day – stomata close to prevent water loss Stomata close – limits CO2 from entering leaves, O2 builds up from light rxns Photorespiration occurs on hot/dry days No ATP produced nor sugar Due to excess O2 instead of CO2 a 2C compound is produced and rearranged and released as CO2 No advantage

Alternate Methods: C4 Plants Minimizes Photorespiration Forms a 4C compound as 1st product (instead of 3) Ex. Sugar cane, corn, grass Photosynthesis occurs between 2 separate cells Mesophyll cells CO2 reacts with Phophonolpyruvate (PEP)  Oxaloacetate (4C cmpd) Bundle Sheath Cells 4C cpmd  CO2  Calvin Cycle

Alternate Methods: CAM Plants Succulent plants ex. Cacti and pinapple Photosynthesis occurs in same cell, but at different times Stomata open at night and close during day Crassulacean Acid Metabolism (CAM) Calvin cycle produces organic acids at night and mesophyll cell store in vacuoles until morning During day light rxns supply ATP and NADPH for Calvin cycle, then CO2 is released from organic acids stored in vacuoles