PHOTOSYNTHESISPHOTOSYNTHESIS

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PHOTOSYNTHESISPHOTOSYNTHESIS

Process that converts light energy to chemical energy

Occurs in chloroplasts of green plants (mostly in leaves)

Contains pigment called chlorophyll

Gives chloroplasts their green color

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ChloroplastChloroplastOrganelleOrganelle where photosynthesisphotosynthesis

takes place.

GranumThylakoid

Stroma

Outer Membrane

Inner Membrane

Thylakoid stacks are connected Thylakoid stacks are connected togethertogether

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CHLOROPLAST STRUCTURE

Enclosed by two membranes

Inner membrane encloses a thick fluid called stroma

Disk-shaped sacs called thylakoids are suspended in stroma

Granum: stack of thylakoids

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PHOTOSYNTHESIS EQUATION

6 CO2 + 6 H2O C6H12O6 + 6 O2

6 carbon dioxide + 6 water glucose + 6 oxygen

Occurs in two main stages: 1. light reactions: happens in thylakoid

membranes 2. Calvin cycle: happens in the stroma

SUN

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Photosynthesis Equation: sunlight

6CO2 + 6 H2O C6H12O6 + 6 O2

sunlight

6 Carbon Dioxide + 6 Water Glucose + 6 Oxygen

Cellular Respiration Equation: C6H12O6 + 6 O2 6 CO2 + 6 H2O + ATP

Glucose + 6 Oxygen 6 Carbon Dioxide + 6 Water

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Convert energy in sunlight to chemical energy

Chlorophyll molecules capture light energy (units called photons)

Captured energy is used to split water molecules photolysis

H2O O2 and H+ ions produced

The Light ReactionsThe Light Reactions

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O2 escapes from leaf as waste product

H+ bonds to NADP+ (electron carrier molecule) forming NADPH

NADPH moves to stroma ATP is produced by light

energy

The Light ReactionsThe Light Reactions

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The Calvin Cycle Glucose made from atoms of CO2,

hydrogen, ATP, and electrons carried by NADPH

Enzymes for Calvin cycle reactions are located outside thylakoids dissolved in stroma

ATP from light reactions provides energy to make glucose

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Calvin cycle reactions are also called the light-independent or dark reactions (can occur without direct light)

Cannot continue indefinitely without two inputs supplied by light reactions:1. ATP2. NADPH

The Calvin Cycle

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Reactions of Photosynthesis.url

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LIGHT ENERGY & PIGMENTS

Visible light: part of the electromagnetic spectrum our eyes detect as different colors

Pigments: chemicals that absorb, transmit, or reflect different wavelengths of light

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CHLOROPLAST PIGMENTS

Absorb blue-violet & red-orange light

Convert absorbed light energy to chemical energy

Green pigments do not absorb green light well:reflect or transmit it backmakes leaves look green

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LIGHT REACTIONS & PHOTOSYSTEMS

Photosystems: clusters of chlorophyll and other molecules in thylakoid membranes of the chloroplast

Two photosystems involved in light reactions

Each photosystem uses a different chlorophyll molecule and performs a different task

Electron transport chain connects the two photosystems and produces ATP

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PHOTOSYSTEM 2

“Water-splitting” photosystem Produces hydrogen ions (H+)

and releases oxygen (O2) as a waste product

Electrons released in splitting H2O are used to make ATP

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PHOTOSYSTEM 1

“NADPH producing” photosystem Light striking another chlorophyll

molecule causes electrons to gain energy and leave the molecule

These electrons along with H+ ions from water are added to NADP+ to produce NADPH

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Photosynthesis - photosystems.url

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What you need to know about the light

reactions Occur on thylakoid membranes Get energy from photons of light Reactants: H2O, light End products: O2, NADPH, ATP

Destination of end products: ATP and NADPH go to stroma

(Calvin cycle) O2 leaves as waste product

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What you need to know about the Calvin

Cycle Uses CO2 and a 5-carbon sugar (RuBP)

along with molecules from the light reactions (ATP & NADPH) to produce glucose—the main cellular fuel

Occurs in the stroma of chloroplast Where do the reactants come from?

RuBP present in stromaCO2 from atmosphereNADPH, ATP from light reactions

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CALVIN CYCLE What are the end products?

3-carbon sugar G3P used by plant cells to produce more complex carbohydrates

•Glucose•starch•cellulose

Where does energy for Calvin cycle come from?ATP produced in light reactions

Where does the Calvin cycle occur? stroma of chloroplast

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SUMMARY OF PHOTOSYNTHESIS

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THE CARBON CYCLE

Process by which carbon moves from inorganic to organic compounds and back

Photosynthesis converts inorganic carbon dioxide to organic compounds

Consumers eat producers and return carbon dioxide to the atmosphere via cellular respiration

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CARBON CYCLE

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PHOTOSYNTHESIS & GLOBAL CLIMATE

Photosynthesis uses CO2 to make sugars

Most organisms give off CO2 in cellular respiration

Total effect of all the organisms on Earth has a large effect on the amount of CO2 in the atmosphere

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Greenhouse Effect• Amount of CO2 in atmosphere has

been increasing rapidly • greenhouse effect: CO2 traps heat

from the sun that would otherwise escape into space

• Increased CO2—mainly from fossil fuels—traps more heat leading to global warming

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GREENHOUSE EFFECT