PHOTOSYNTHESIS chapter 6 Capturing the energy in light

PHOTOSYNTHESISchapter 6

Capturing the energy in light

WHAT IS PHOTOSYNTHESIS?

The process of transferring the energy in light (electromagnetic radiation)

into the energy of carbohydrates (organic compounds).

Light -------> chemical energy

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sunlight + 6 CO2 + 6 H20 --> C6H12O6 + 6 O2

WHICH ORGANISMS DO PHOTOSYNTHESIS? WHICH ONES DON’T?

AUTOTROPHS “self feeders” do. Ex. PLANTS & kelp, sea weed, filamentous algae & some protists

(Eukaryotic cells with chloroplasts) & also… CYANOBACTERIA (photosynthetic bacteria)

HETEROTROPHS “other feeders” don’t. Ex. Animals, Decomposers (fungi), some bacteria &

protists. (Cells without chlorophyll/chloroplasts)

WE COULDN’T EXIST WITHOUT PRODUCERS… WHY???

producer herbivore

carnivore

carnivore

saprophyte

HEAT

CONSUMERS

SUN ---> PRODUCERS--> CONSUMERS ------------->

Plants transform energy in sunlight into chemical energy.

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There’s a LOT of photosynthesis going on in this rainforest!Why are rainforests called “THE LUNGS OF THE EARTH?”

WHERE DOES PHOTOSYNTHESIS HAPPEN?

Organ?Cells?Organelle?

WHERE DOES PHOTOSYNTHESIS HAPPEN?

Organ:LEAVES

Tissue:MESOPHYLL cells

Organelle:CHLOROPLASTS

DRAW & LABEL THE CROSS SECTION (side view) OF A LEAF…

Label the:Waxy cuticleGuard cellsVein xylem & phloemPalisade Mesophyll layerSpongy Mesophyll layer

LEAF

waxy cuticle

palisadespongy

stoma/stomataGUARD CELLS

chloroplast

DRAW AND LABEL THE PARTS OF A CHLOROPLAST:

Outer membraneInner membrane/thylakoid membraneThylakoidGranumGranaStroma

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HOW DOES PHOTOSYNTHESIS WORK?

BIOCHEMICAL PATHWAY A complex series of chemical reactions that are linked together.

The products of one reaction are consumed (are reactants) in the next set of reactions.

TWO SETS OF REACTIONS:1. The Light Reactions

occur on the thylakoid membrane… creates ATP & NADPH2. The Calvin-Benson Cycle or C3 Cycle

aka: the light “independent” reactions, dark reactions occur in the stroma…. Use ATP & NADPH to power the

endergonic process of creating glucose from CO2.

ENERGY MOLECULES TRANSPORT ENERGY ATP transports energy in the form of phosphate groups. When it transfers a phosphate groups to another molecule it becomes ADP.

NADPH transports energy in the form of electrons and protons. When it transfers electrons

and protons to another molecules it becomes NADP+.

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PART ONE: THE LIGHT REACTIONS

LIGHT REACTIONS USE “VISIBLE LIGHT” 750-350nm

HOW IS LIGHT ENERGY ABSORBED AND USED?

PIGMENT PROTEINS in the thylakoid membrane absorb photons of light and use this energy to “excite” electrons.

Create electricity to do work!!!!

CHLOROPHYLL A absorbs red light Accessory Pigments: CHLOROPHYLL B absorbs blue light CAROTENOIDS PHYCOCYANINS XANTHOPHYLL

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The Light Reactions of photosynthesislight + water + chlorophyll --> oxygen gas + ATP + NADPH

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Energy transfers recap: 1.Photons of light (radiant energy) move 2.Supercharged electrons from WATER through the ETC proteins, which power the 3.Proton Pump (active transport/kinetic energy); which pumps protons into the

thylakoid space creating a 4.Proton Gradient (potential energy) which results in 5.Chemiosmosis of Protons (passive transport/ kinetic energy) through ATP Synthase

channels/enzyme which results in the bonding of Pi to ADP 6.Synthesis of ATP 7.Electrons are passed to NADP+ (final electron acceptor) to form NADPH (reduction).

LIGHT IS CONVERTED TO THE ENERGY MOLECULES: ATP and NADPH which power the Calvin cycle.

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THE LIGHT REACTIONS are the first set of reactions in photosynthesis.

What must be embedded in the thylakoid membranefor these reactions to occur????

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Embedded in the phospholipid bilayer (in this order):water splitting enzyme, photosystem 2, Electron transport chain cytochrome proteins, proton pump, photosystem 1, Electron transport chain cytochrome proteins, NADP+ reductase enzyme, ATP synthase channel.

And the reactants/substrates: NADP+, H20, ADP and Pi.

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Photosystem 1Photosystem 2

1. Photons of light are absorbed by light absorbing pigmentswithin photosystems 2 &1 (combine the collected energy.) 2. Super charged electrons leave the reaction center w/in Chlorophyll A and are passed down the Electron Transport Chain of cytochrome proteins.

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Photosystem 1Photosystem 2

3. Water provides electrons to the E.T.C4. Moving electrons provide the energy needed to power the proton pump, which pumps H+ into the thylakoid space.THIS CREATES A CONCENTRATION GRADIENT.5. NADP+ picks up the electrons at the end of the chain and is reduced to NADPH (ELECTRON CARRIER MOLECULE).

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Photosystem 1Photosystem 2

6. Protons diffuse out to the stroma through an ATPsynthase ion channel = CHEMIOSMOSIS.7. The moving protons provides the energy needed to add an inorganic phosphate onto ADP to create ATP.8. NADPH and ATP are the energy molecule products of the light reactions. They are reactants (used) in the Calvin Cycle

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CHEMIOSMOSIS diffusion of H+ through ATP synthase

High concentrationof protons inside thethylakoid space.

Low concentrationout in the stroma.

Protons diffuse outinto the STROMAwhere ATP is made.

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Photosystem 1Photosystem 2

LET’S SEE THE PROCESS STEP BY STEP…

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PS1PS 2

water splitting enzyme

proton pump

ATP synthaseH+ channel

NADP+

electron transport chain

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PS1PS 2

water splitting enzyme

proton pump

ATP synthaseH+ channel

NADP+

electron transport chain

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PS1PS 2

water splitting enzyme

proton pump

ATP synthaseH+ channel

NADP+

electron transport chain

ATP

NADPH

LAB: PAPER CHROMATOGRAPHY OF PLANT PIGMENTS…

A technique for separating and identifying pigments and other molecules from cell extracts.

The solvent moves up the paper by capillary action and carries the mixture of photosynthetic pigments with it.

One by one, the heavy pigments fall from the solvent to the paper. The lightest pigment gets carried the farthest distance.

DIRECTIONS:1) Use a dime or quarter to press

chloroplasts through the stomata of a spinach leaf to make a thick line of pigment mixture on your chromtography paper.

2) Dip only the pointy tip of the paper in the solvent.

3) Put the stopper on the tube.4) Watch the solvent move up the

paper and separate the different light absorbing pigments that allow photosynthesis to occur!!!!

5) Take your paper out and measure the distances from the original line to the bottom of each band of color and to the top of the “solvent front”.

6) You should see 4 pigment/color bands.

Olive-Green = chlorophyll BBlue-Green = chlorophyll AYellow = xanthophyllOrange = caroteen

•One strip per student.•One BIG strip per group.

CHROMATOGRAPHY

Put your results in a Table.

Band # Distance (mm) Color

1

2

3

4

solvent

Calculate the Rf for each pigment

Rf = Distance pigment migrated Distance solvent migrated

Analysis:1.How do you think your Rf values will compare with others? Should

they be similar or different? Why?2.What factors are involved in the separation of pigments?3. What is the main photosynthetic pigment of plants? What are the

accessory pigments?4. What do these pigments do?5. If leaves are usually green because of the mixture of these

pigment molecules, but turn red and yellow in the Autumn before they drop their leaves what do you think is happening?

THE CALVIN CYCLE Second set of reactions in photosynthesis

Uses the energy produced from the light reactions (ATP & NADPH) to form glucose

from atmospheric CO2.

Named after MELVIN CALVIN 1911-1997

THREE STEPS OF THE CALVIN CYCLE(this biochemical pathway reforms the first molecule RuBP so it is called a cycle)

1. CARBON FIXATIONThe enzyme RUBISCO fixes (joins) 3 molecules of CO2 to 3 molecules of

5-carbon RuBP to make 3, 6-carbon molecules which split in half to form 6 molecules of PGA

2. PGAL SYNTHESIS Each molecule of PGA is converted into a molecule of PGAL (uses 6 ATP

& 6 NADPH, 1 of each per PGA)3. RuBP REFORMATIONOne ATP is used per RuBP reformed. Most of the PGAL is converted

back into RuBP but 2 molecules will be used to make a sugar (glucose).

THE CYCLE OCCURS TWO TIMES TO MAKE 1 GLUCOSE

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Balance Sheet for Photosynthesis

TO make 1 glucose the Calvin Cycle

- fixes 6 CO2

- uses 18 ATP

- uses 12 NADPH

BALANCED EQUATION

Reactants

light + 6 CO2 + 6 H2O -->

Products

C6H12O6 + 6 O2

BALANCED EQUATION

Reactants

light + 6 CO2 + 6 H2O -->

Products

C6H12O6 + 6 O2

GRAPH:EFFECTS OF LIGHT INTENSITY ON PHOTOSYNTHESIS

Explain the graph. Why would the rate of photosynthesisBe different for the fern and the corn plants?

A C3 plant will close its stomata on a hot day to prevent water loss.

Oxygen builds up, the Calvin Cycle halts. No more sugar is made.

Corn and sugar cane are adapted for dry heat all the time.

GRAPH:EFFECTS OF LIGHT INTENSITY ON PHOTOSYNTHESIS

C-4 PATHWAY EX. Corn, sugar cane, crab grass

Alternative pathway fixes CO2 into a 4 carbon compound- during the hottest part of the day the stomata are partially closed.

Contain an enzyme that converts low levels of CO2 into the 4 carbon compound even when O2 levels are high. Later the 4 C is shuttled to bundle sheath cells & is used as a source of CO2 for the the Calvin cycle.

Loses about half as much water as C 3 plants.

CAM PLANTS EX. Cactuses & Pineapples

Only open stomata at night. They use the C4 pathway to store CO2 as

part of Malic Acid in vacuoles during the night.

light reactions occur during the day and the Calvin Cycle but since the stomata are CLOSED during the day there is no CO2 getting in. The source of CO2 is breaking down the Malic Acid… not atmospheric CO2.

The end.