ap bio ch 10, part 1
TRANSCRIPT
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PHOTOSYNTHESISPHOTOSYNTHESISThe Process That Feeds the
Biosphere•All organisms either directly or indirectly depend on photosynthesis
•Autotrophs-Produce organic molecules from CO2 & other inorganic materials
•Heterotrophs-
*Plants, algae, & some protists are photoautotrophs, they use light to synthesize glucose
Depend on organic compounds produced by other organisms
“self-feeders” Consumers
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All heterotrophs depend on autotrophs for food and the oxygen that’s a
biproduct of photosynthesis
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Photosynthsis Converts Light Energy to Chemical Energy
of FoodWhich organelle is responsible for photosynthesis??
Chloroplasts
What is the chemical energy that autotrophs produce??Glucose
What are the raw materials that go into photosynthesis? What are the products?6CO2+ 6H2O+ Light Energy C6H12O6+ 6O2
Which plant organ is the primary site of photosynthesis?Leaves
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Anatomy of the Leaf & Its Chloroplasts
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How do we know what we know about
photosynthesis??Tracking Atoms:The overall chemical reaction of photosynthesis is the reverse of cell respiration, but the process of photosynthesis is NOT the reverse of cell respiration:
What’s the equation for cell respiration?
C6H12O6 + 6O2 6CO2 + 6H2O + ATP energy
What’s the equation for photosynthesis?
6CO2 + 6H2O + light energy C6H12O6 + 6O2
If you don’t already have these equations memorized, write them down and commit them to memory!!
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Sunlight
Photosynthesis
Cellularrespiration
Heat
Relationship Between Cell Respiration & Photosynthesis
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Photosynthesis Equation in its Simplest Form:
CO2 + H2O [CH2O] + O2
General formula for a carbohydrate
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The Splitting of WaterThe Splitting of WaterBefore the 1930’s, it was widely believed that the O2
produced by plants is a result of the splitting of CO2 during photosynthesisThanks to C.B. van Niel & others, we now know that the O2 produced is a result of the splitting of a water molecule during photosynthesis:
Van Niel’s Experimental ResultsSulfur bacteria: CO2 + 2H2S [CH2O] + H2O + 2S
Plants: CO2 + 2H2O [CH2O] + H2O + O2
General: CO2 + 2H2X [CH2O] + H2O + 2X
Conclusion: photosynthetic organisms require a hydrogen source which is split during
photosynthesis
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Later Tests Using Oxygen-18 Isotope Markers Confirmed the
Same….Exp #1: When the oxygen in water is labeled…CO2 + 2H2O [CH2O] + H2O + O2Exp #2: When the oxygen in carbon dioxide is labeled…
CO2 + 2H2O [CH2O] + H2O + O2
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Tracking Atoms Through Photosynthesis….
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Quick Think
• With someone near you, discuss: With someone near you, discuss: where does the oxygen released where does the oxygen released from plants during photosynthesis from plants during photosynthesis come from and how did scientists come from and how did scientists determine thisdetermine this? ?
• Be prepared to share your ideas.Be prepared to share your ideas.
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Photosynthesis as a Redox Photosynthesis as a Redox ProcessProcessCell Resp Photosynthesis
Employs redox reactions
Employs redox reactions
e- lose potential energy as they move down ETC
e- gain potential energyrequires energy from light
By-product = H2O By-product = O2
Gain or Lose?
Gain orLose?
? ?
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Photosynthesis Overview
Go to your diagrams
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Two Stages of Photosynthesis: Light
Reactions & Calvin CycleLight Reactions:
•Light is absorbed by chlorophyll•Energy from the light splits H2O•H from water reduces NADP+ (an e- acceptor) to NADPH•Chemiosmosis makes ATP from ADP. This process is known as photophosphorylation
•Products of light reactions:Energy = ATP & NADPHBy-product = O2
Occurs in thylakoid
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Two Stages of Photosynthesis: Light
Reactions & Calvin CycleThe Calvin Cycle:•CO2 from atmosphere enters chloroplast & is incorporated into organic molecules = carbon fixation•NADPH from the light rxns reduces the fixed carbon (by donating H) to carbohydrate; ATP from light rxns is required for this step
•Product of Calvin Cycle:glucose
Occurs in stroma
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The Light Reactions of
Photosynthesis
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The Light Reactions Convert Solar Energy to the Chemical
Energy of ATP & NADPHThe Nature of Sunlight (electromagnetic energy):
•Light has properties of both waves & particles (photons)•Visible light is the part of the EMS that drives photosynthesis
•The shorter the wavelength, the higher the energy
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Photosynthetic Pigments are Light Receptors
•Pigments like chlorophyll either absorb, transmit, or reflect light•The wavelength of light that is reflected is the color that we detect with our eyes•Which wavelength (color) of Light is least effective for Photosynthesis??Green
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These accessory pigments allow chloroplasts to take advantage of a broader spectrum
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Quick Think
•With someone near With someone near you discuss: you discuss: Why are Why are plants greenplants green? ?
•Be prepared to share Be prepared to share your thoughtsyour thoughts
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Excitation of Chlorophyll by Light
•Energy from a photon of light raises a pigment molecule’s e- from ground state to an unstable excited state •When the e- drops back down to its ground state, energy is emitted in the form of heat & light•Chloroplasts in plants don’t fluoresce because the excited e- is passed to an e- acceptor rather than dropping back down to ground state
Go to your diagrams
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A photosystem is a bundle of pigment molecules and
proteins•Photosystems act as an antenna for light
Made of 2 chlorophyll a molecules & a primary e- acceptor
Special because they can use light to boost an e- to the next energy level…light energy has now been converted to chemical energy
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The thylakoid has 2 photosystems: PS I & PS II
Chlorophyll a molecules that best absorb light at 680 nm & 700 nm respectively
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Noncyclic Electron Flow: PS I & PS II work together to use light to make ATP &
NADPH during the light reactionsDuring the light reactions, e- may flow in either a cyclic or noncyclic manner:Noncyclic flow of e-
plastoquinone
plastocyanin
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Noncyclic Electron Flow: PS I & PS II work together to use light to make
ATP & NADPH during the light reactions
http://www.cst.cmich.edu/users/baile1re/bio101fall/enzphoto/photoanima.htm#
http://www.stolaf.edu/people/giannini/flashanimat/metabolism/photosynthesis.swf
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html#
Animation of steps:
Noncyclic flow of e-
Go to your diagrams
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Quick Think
• With someone near you,With someone near you, summarize summarize the steps of noncyclic electron flow the steps of noncyclic electron flow in the light reactionsin the light reactions
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Cyclic Electron Flow: uses PS I but not PS II
During the light reactions, e- may flow in either a cyclic or noncyclic manner:
•Only ATP is produced, not NADPH
Cyclic e- Flow•Noncyclic e- flow produces NADPH & ATP •BUT the Calvin cycle uses more ATP•SO Cyclic e- flow is used to keep up with the ATP demand so that the Calvin cycle doesn’t stop
Go to your diagrams
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Quick Think
• With someone near you, discuss the differences between noncyclic and cyclic electron flow
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Comparing Chemiosmosis in
Mitochondria and Chloroplasts
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Comparing Chemiosmosis in Chloroplasts & Mitochondria
In both organelles, the ETC pumps H+ ions from an area of low concentration to an area of higher concentration. The diffusion of H+ through ATP synthase drives ATP synthesis
Similarities
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Comparing Chemiosmosis in Chloroplasts & MitochondriaDifferences
•In mitochondria chemical energy from food is transferred to ATP & NADH. •In Chloroplasts light energy is transfered to ATP & NADPH• H+ diffuse across inner
membrane to matrix in the mitochondrion•H+ diffuse out of the thylakoid & into the stroma of the chloroplast.