ch 6 photosynthesis
DESCRIPTION
6-1: THE LIGHT REACTIONS. Ch 6 PHOTOSYNTHESIS. Light energy absorbed by pigments in photosystems on thylakoid membrane PS II first, then PS I 1. Sunlight energizes electrons at PSII 2. e - picked up by Primary Electron Acceptor Electrons lost are replaced from water - PowerPoint PPT PresentationTRANSCRIPT
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CH 6PHOTOSYNTHESIS
6-1: THE LIGHT REACTIONS
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ENERGY CONVERSION: LIGHT TO CHEMICAL
Light energy absorbed by pigments in photosystems on thylakoid membrane
PS II first, then PS I1. Sunlight energizes electrons at PSII2. e- picked up by Primary Electron Acceptor Electrons lost are replaced from water H2O splitting enzyme splits water
H2O H+ + e- + O2
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ENERGY CONVERSION: LIGHT TO CHEMICAL
3. e- move down electron transport chain (ETC) to PS I
e- lose energy Energy used to create H+ gradient in
thylakoid 4. Light re-energizes e- at PSI5. energized e- picked up by NADP+ to make NADPH
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CARRIER MOLECULE Compound that can accept a
pair of high energy electrons and transfer them along with most of their energy to another molecule
Ex.) NADP+
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Q: WHAT DOES THIS DO? NADP+ NADPH A: this traps sunlight in chemical
form
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ENERGY CONVERSION: LIGHT TO CHEMICAL
Light rxn creates H+ gradient inside thylakoid
Concentration higher inside thylakoid Lower in stroma
H+ move through ATP synthase to generate ATP
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WHAT’S THE POINT OF THE LIGHT REACTION?
To make some ATP To make NADPH
Which will be used to make sugar
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WHY ALL THE ACRONYMS??? NADP+ = nicotinamide adenine dinucleotide phosphate RuBP = ribulose biphosphate 3-PGA= 3-Phosphoglyceric acid G3P = glyceraldehyde 3-phosphate
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THE CALVIN CYCLE These reactions don’t require
light, therefore these reactions are called
Light – independent reactions
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THE CALVIN CYCLE 2nd set of reactions in photosynthesis In stroma Plants use energy stored in ATP and
NADPH to make sugars
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CARBON FIXATION Incorporation of CO2 into organic compounds 3CO2 must enter cycle to make a 3Carbon sugar
Need 3 C to make a 3-carbon sugar. How many 3-carbon sugars are needed to make
a sugar like glucose?Glucose is C6H12O6. So we need two 3-carbon sugars to make one 6-carbon sugar like
glucose.So… it takes two cycles through the Calvin
cycle to produce one 6-carbon sugar.
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WHAT OTHER 6-CARBON SUGARS ARE THERE?
Fructose Galactose
These sugars all share the chemical formula C6H12O6.
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CALVIN CYCLE1. CO2 combines with Ribulose
biphosphate (RuBP), a 5C molecule(What is 1 + 5?)
-Resulting 6C molecule is unstable and breaks in half (6/2=?) forming a 3C molecule 3-PGA2. 3-PGA converted into G3P using
energy from NADPH and ATP
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CALVIN CYCLE3. One G3P leaves cycle-is used to make organic compounds like glucose4. Remaining G3P molecules are converted back into RuBP using ATP
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ALTERNATIVE PATHWAYS Plants that live in hot & dry places fix
carbon in different ways Plants lose water rapidly
Water lost through pores on leaves called Stomata
CO2 and O2 also move through these pores
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ALTERNATIVE PATHWAYS C4 pathway Stomata stays closed during hot parts
of day Corn, sugar cane, crab grass (tropical
environments) CAM pathway Stomata only open at night Pineapple, cactus
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FACTORS THAT INFLUENCE PHOTOSYNTHESIS
Light intensity- increases rate of photosynthesis up to a point
CO2 levels- increases rate up to a point
Temperature- increases rate to a point, then drops Necessary proteins are
destroyed at high temps