HBio: Photosynthesis

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HBio Photosynthesis
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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

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Homework

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

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Do Now

• Homework on Desk
• Grab your clickers!

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Which leaf structure is responsible for gas
exchange?

1. Epidermis
2. Cuticle
3. Mesophyll
4. Guard cells
5. Xylem
6. Phloem

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Which leaf structure is responsible for transport
of water?

1. Epidermis
2. Cuticle
3. Mesophyll
4. Guard cells
5. Xylem
6. Phloem

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Which leaf structure is responsible for synthesis
of sugars?

1. Epidermis
2. Cuticle
3. Mesophyll
4. Guard cells
5. Xylem
6. Phloem

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(No Transcript)
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Which process increases C in the atmosphere?

1. Reforestation
2. Coal formation
3. Burning fossil fuels

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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

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Electromagnetic Spectrum
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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 pigments light
  absorption vs. wavelength

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ALL wavelengths are equally effective for
photosynthesis

1. True
2. False
3. Cannot be determined

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The colors of light most useful in photosynthesis
are

1. green, yellow, and orange
2. red, violet, and blue
3. infrared, red, and yellow
4. red, white, and blue

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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

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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

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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

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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

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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)

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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

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Classwork

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

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Do Now

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

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The light dependent reactions take place in the

1. Cloroplast membrane
2. Thylakoid
3. Stroma
4. Cytoplasm

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NADP ? NADPH is an example of

1. Reduction
2. Oxidation
3. Chemiosmosis
4. Photophosphorylation
5. None of the above

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During what stage of photosynthesis is O2
produced?

1. Photosystem I
2. Photosystem II
3. ETC
4. Photophosphorylation
5. O2 is not produced

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The photophosphorylation of ATP is due to

1. Chemiosmosis of H
2. ATP synthase
3. Electron Transport Chain
4. All of the above
5. None of the above

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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!

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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

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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

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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