Photosynthesis

Photosynthesis1IntroductionAutotrophs:

Photoautotrophs :

Chemoautotrophs2Important structures

Chloroplast

Thylakoids:

Grana:

Stroma:

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stromathylakoid compartmentthylakoid membrane systemtwo outer membranesChloroplastOrganelle of photosynthesis in plants and algae

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a A look inside the leafb One of the photosynthetic cells inside leafleafs upper epidermisphotosynthetic cell in leafleaf veinleafs lower epidermisLeaf Structure556

Properties of LightWhite light from the sun is composed of a range of wavelengths.

All colors778

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ChlorophyllChlorophyll is the main pigment that absorbs sunlight.

Chlorophyll absorbs blue light and to a lesser extent, red light.

It reflects green light 10What do chlorophyll and fireworks have in common?1111Photosynthesis: Light-DependentPhotosystems - chlorophyll a molecule....12What does Chlorophyll absorb?13

1414Figure 4-15 (part 1) Capturing light energy with excited electrons. Chlorophyll electrons are excited to a higher energy state by light energy.Photosynthesis: Light-Dependentpigment absorbs light energy15Two Potential Fates of Excited ElectronsElectron returns to resting, unexcited state.

Excited electrons are passed to other atoms.1616An electron in a photosynthetic pigment that is excited to a higher energy state generally has one of two fates (refer to the next two slides also): (1) The electron returns to its resting, unexcited state. In the process, energy is released, some of which may be transferred to a nearby molecule, bumping electrons on that molecule to a higher energy state (and the rest of the energy is dissipated as heat) or (2) The excited electron itself is passed to another molecule.

1717Figure 4-15 (part 2) Capturing light energy with excited electrons.Chlorophyll electrons are excited to a higher energy state by light energy. Photosynthesis: Light-Dependentelectrons in the pigments become excited

energy (but not the electrons) is transferred

excites the electrons in a chlorophyll a molecule at the center of the photosystem. 18Photosynthesis: Light-Dependent

19The Passing of Electrons in Their Excited StateMolecules that gain electrons always carry greater energy than before receiving them

2020The passing of electrons from molecule to molecule is one of the chief ways that energy moves through cells. Many molecules carry or accept electrons during cellular activities. All that is required is that the acceptor have a greater attraction for electrons than the molecule from which it accepts them. Photosynthesis: Light-Dependentchlorophyll that is the reaction center

Splits water2122

Photosynthesis: Light-DependentPhotosynthesis: Light-Dependentchlorophyll a continually loses its excited electrons to a nearby molecule,

replacement electrons come from water.

23Photosynthesis: Light-Dependent

24Photosynthesis: Light-DependentProtons rush out of the thylakoid sacs with great forceto build energy-storing ATP molecules25Light-Dependent26Photosynthesis: Light-DependentProduct #1 of the Photo Portion of Photosynthesis: ATP

Product #2: NADPH

Product #3 (waste): O2

27Photosynthesis Equation

6H2O + 6CO26O2 + C6H12O6 6 water +6 carbon dioxide6 oxygen + glucoseLIGHT ENERGY28Suppose a large meteor hit the earth. How could smoke and soot in the atmosphere wipe out life far beyond the area of direct impact?29PhotosynthesisTwo stages:30Light-dependent Reactionsrequire light to work31smoke and soot32smoke and soot33smoke and soot34Light-independent Reactionsdo not require light35

sunlightWhere the two stages of photosynthesis occur inside the chloroplast light-dependent reactionslight-independent reactionsCO2sugarsNADPH, ATPNADP+, ADPO2H2OTwo Steps in Photosynthesis3636Calvin Cyclewhether or not light is present.Occur in the stroma37Photosynthesis: Light-inDependentLight-inDependenttake the energy from ATP + energized ions from NADPH + carbon dioxide to make glucose or sugar.

carbon dioxide into CH2O.

38Photosynthesis: Light-inDependent39

Summary of Photosynthesis

12H2OsunlightCalvin-Bensoncycle6O2LightDependentReactionsLightIndependentReactionsNADP+ADP + Pi6 RuBP12 PGALPend products (e.g., sucrose, starch, cellulose)phosphorylated glucose6H2O6CO2ATPNADPHPhotosynthesis: Light-inDependent41

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C3 Plants4445

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C4 Plants4748

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CAM Plants5152

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Factors that Affect Rates3 factors can limit the speed of photosynthesis: light intensity, CO2 concentration, temperatureWithout enough light, a plant cannot photosynthesize very quickly, even if there is plenty of water and CO2 .

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Factors that Affect Rates55Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesize if there is insufficient carbon dioxide.

Factors that Affect RatesIf it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesize if it gets too hot.

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Linked ProcessesPhotosynthesisEnergy-storing pathway Releases oxygenRequires carbon dioxideAerobic RespirationEnergy-releasing pathwayRequires oxygenReleases carbon dioxidePhotosynthesis: The MovieAnimationMovie58