AP BIOLOGYPHOTOSYNTHESIS

Chapter 10Light Reactions

http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0076.JPG

http://vilenski.org/science/safari/cellstructure/chloroplasts.html

Sunlight is made upof many different_______________of light

Your eyes “see”different wavelengths asdifferent ___________

http://www.simontucket.com/_Portfolio/PortLarge/L_Il_Prism.jpg

wavelengths

colors

Visible light is part of electromagnetic spectrum

ROYGBIV

pigments

By: VanderWal

Plants gather the sun’s energy with light absorbing molecules called _______________.

The main energy absorbing moleculein green plants is__________________

http://fig.cox.miami.edu/Faculty/Dana/chlorophyll.jpg

CHLOROPHYLL a

Plant pigment molecules are amphiphatic, meaning they have a hydrophobic domain (for membrane insertion) and

a hydrophillic domain facing the “watery” cytoplasm.

Chlorophyll a is UNIVERSAL for oxygen evolving, photosynthetic organisms.

The differences in the the types of chlorophylls are minute, yet these structural changes affect the energy of the ejected electron (from the via the magnesium metal atom).

Evidence for evolutionary relationship between all oxygen-evolving organisms lies in their sharing of the chlorophyll a molecule.

The conjugated double bonds in the “ring” structure of the The conjugated double bonds in the “ring” structure of the pigment molecules allow the electron clouds to shift or pigment molecules allow the electron clouds to shift or

“resonate” when exposed to light. This excitation by light is “resonate” when exposed to light. This excitation by light is known as the “Photoelectric Effect.”known as the “Photoelectric Effect.”

– Photoelectric effect

– http://phet.colorado.edu/en/simulation/photoelectric

– Click Run Now

– As light strikes surface of metal (or atoms in the pigment), electrons are ejected at certain energy at specific wavelengths.

– These electrons that are lost by the chlorphyll molecule are replaced by the hydrolysis of water by an adjacent enzyme complex.

Species are classified by their different accessory pigments

Chromatography as a evolutionary diagnostic tool.

CAROTENOID PIGMENTS appear ORANGE, RED, and YELLOW

Carotene appears orange

Xanthophyll appears yellow

http://www.rnzih.org.nz/images/gardenimages/carrots_d.jpg

http://www.webexhibits.org/causesofcolor/images/content/7C_chlorophyll_in_leaves.jpg

Pigments of photosynthesis

• Chlorophyll & other pigments– embedded in thylakoid membrane– arranged in a “photosystem”– structure-function relationship

Light: absorption spectraPhotosynthesis gets energy by absorbing

wavelengths of light– chlorophyll a

• absorbs best in red & blue wavelengths & least in green

– other pigments with different structures absorb light of different wavelengths

WHY ARE PLANTS GREEN?

We “see” reflected lightLight wavelengths that are reflectedbounce back to your eyes . . . so leaves “LOOK” green.

Image modified from: http://www.visibledreams.net/Web/color/color_3.html

WHY DON’T WE SEE THE OTHER PIGMENTS?

Carotenoids are usually hidden by the presence of chlorophyll

In the fall chlorophyll production shuts down and other pigments “show”

http://sps.k12.ar.us/massengale/ecology_notes_bi.htm

http://www.litzsinger.org/weblog/archives/email%20AutumnTrees5%20LREC%20102605.jpg

PHOTOSYNTHESIS HAPPENS IN CHLOROPLASTS

= sac-like

photosynthetic = stack of thylakoids

membranes

inside chloroplast

THYLAKOIDSGRANUM (pl. grana)

Image from BIOLOGY by Miller and Levine; Prentice Hall Publishing©2006

SPACESTHYLAKOIDSPACE(lumen)

STROMA

cytoplasm

http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0076.JPG

Gel-filled spaceInside the thylakoid

sac

Gel-filled space inside

chloroplast surrounding

thylakoid sac

Gel-filled space OUTSIDE chloroplast but inside the cell membrane

PHOTOSYNTHESIS OVERVIEW

Pearson Education Inc; Publishing as Prentice Hall

Phosphate groups

Ribose

Adenine

LIGHT DEPENDENT REACTIONS CHARGE UP ENERGY CARRIER = _____ATP

P

i

ADP

Energy for cellular work(Energy- consuming)

Energy from catabolism(Energy- yielding)

ATP

+

High energy electron carrier = _____________NADP+

NADP+ + 2e- + H+ → NADPH

NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE

Photosynthesis

• Light reactions– light-dependent reactions– energy production reactions

• convert solar energy to chemical energy• Make ATP & NADPH

• Calvin cycle– light-independent reactions– sugar production reactions

• use chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6

Photosystems of photosynthesis

2 photosystems in thylakoid membrane– Both have a REACTION CENTER

• CHLOROPHYLL a molecules • PRIMARY ELECTRON ACCEPTOR

– Surrounded by light-gathering “ANTENNA COMPLEX” • Accessory pigments (chlorophyll b, carotenoids)

– Collect light energy and pass it on to chlorophyll a

– Photosystem II• P680 = absorbs 680nm

wavelength red light

– Photosystem I• P700 = absorbs 700nm

wavelength red light

ETC of PhotosynthesisPhotosystem II

Photosystem I

ELECTRON TRANSPORT CHAIN

• Plastoquinone• Cytochrome• Plastocyanin• Ferredoxin

Light Dependent reactionsElectron Transport Chain

– membrane-bound proteins in organelle– electron acceptors

• NADPH

– proton (H+) gradient across inner membrane• Where’s the double

membrane?

– ATP synthase enzyme

H+H+

H+

H+H+H+

ETC of PhotosynthesisChloroplasts transform light

energy into chemical energy of ATP

use electron carrier NADPH

LIGHT DEPENDENT REACTIONSETC produces from light energy

– ATP & NADPH• go to Calvin cycle

PS II absorbs light– excited electron passes from chlorophyll to

“primary electron acceptor”– need to replace electron in chlorophyll– enzyme extracts electrons from H2O &

supplies them to chlorophyll• splits H2O• O combines with another O to form O2

• O2 released to atmosphere• and we breathe easier!

ETC of Photosynthesis

H+

H+

13

4

H+

ADP + Pi

H+H+

H+

H+ H+

H+H+H+

ATP

to theCalvin Cycle

12

H+

H+

3

4

H+

ADP + Pi

H+H+

H+

H+ H+

H+H+H+

ATP

ETC of Photosynthesis

to theCalvin Cycle

ETC of Photosynthesis

6

5

$$ in the bank…reducing power

to theCalvin Cycle

electron carrier

ETC of Photosynthesis

split H2O

MAKING ATP

• moves the electrons • runs the pump• pumps the protons• forms the gradient• drives the flow of protons

through ATP synthase

• attaches Pi to ADP

• forms the ATP

H+

ADP + Pi

H+H+

H+

H+ H+

H+H+

H+

ATP

Noncyclic Photophosphorylation

• Light reactions elevate electrons in 2 steps (PS II & PS I) – PS II generates

energy as ATP– PS I generates

reducing power as NADPH

Cyclic photophosphorylationPS I doesn’t pass

electron to NADP…it cycles back to ETC & makes more ATP, but no NADPH– coordinates light

reactions to Calvin cycle– Important in maintaining

proportion of ATP &NADPH for Calvin

– Calvin cycle uses more ATP than NADPH

X

Photophosphorylation

noncyclicphotophosphorylation

cyclicphotophosphorylation

6CO2 6H2O C6H12O6 6O2light

energy →+ ++

Experimental evidence

• Where did the O2 come from?

– radioactive tracer = O18

6CO2 6H2O C6H12O6 6O2light

energy →+ ++

Experiment 1

6CO2 6H2O C6H12O6 6O2light

energy →+ ++

Experiment 2

Proved O2 came from H2O not CO2 = plants split H2O

LIGHT DEPENDENT REACTIONRequires ______________Molecules embedded in

________________________Made up of __________________ connected by ______________________ & ___________________Uses light energy to change

ADP + P → _______NADP+ + 2e- + H + → _________

Breaks apart ______ molecules and releases _____________

LIGHT

ATP

THYLAKOID membranes

PHOTOSYSTEMS II & I ELECTRON TRANSPORT CHAIN

NADPH

H20oxygen

ATP SYNTHASE

LIGHT REACTIONS summary Where did the energy come from?

Where did the electrons come from?

Where did the H2O come from?

Where did the O2 come from?

Where did the O2 go?

sunlight

From chlorophyll; replaced by H2O

In through roots

Made when water splits

Out through stomata

LIGHT REACTIONS summary Where did the H+ come from?

Where did the ATP come from?

What will the ATP be used for?

Where did the NADPH come from?

What will the NADPH be used for?

…stay tuned for the Calvin cycle

Split off of water

Produced by ATP synthase during light rxns

Make sugar in Calvin cycle

Receives e-’s at end of ETC

Make sugar in Calvin cycle

PHOTOSYNTHESIS

Light-Dependent Reaction

Light-IndependentReactions

CALVIN CYCLE

Light & Water

Oxygen

ATP

NADPH

Carbon Dioxide (CH2O)n

CALVIN CYCLE

http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0076.JPG

http://vilenski.org/science/safari/cellstructure/chloroplasts.html

Calvin Cycle

See Calvin cycleanimation

**

*

*Molecules you

need to know

X 2

CALVIN CYCLE MOLECULES5 carbon CO2 acceptor that combines with

CO2 in the first step of the Calvin cycle________________________________

Enzyme that catalyzes the addition of CO2 to RuBP

________________________

3 carbon sugar produced during the Calvin cycle that can be used to build glucose and other organic molecules

______________________________

Ribulose bisphosphate (RuBP)

RuBP carboxylase (RUBISCO)

Glyceraldehyde-3-phosphate (G3P)

CALVIN CYCLE (also called _________________________)

____________ require ____________

Happens in _________ between thylakoidsNADPH donates _______________

ATP donates _________________CO2 donates ______________

to make __________________________

LIGHT

LIGHT INDEPENDENT

ENERGY

STROMAHydrogen ions + electrons

Carbon & oxygenglyceraldehyde-3-phosphate (G3P)

http://www.estrellamountain.edu/faculty/farabee/biobk/BioBookCHEM2.html

DOES NOT

To make one glucose moleculeC6H12O6

the Calvin cycle uses

_____ molecules of CO2

_____ molecules of ATP

_____ molecules of NADPH

6

18

12

Campbell concept check 10.3

CALVIN CYCLE summary

Where does the C in G3P come from?

Where does the H in G3P come from?

Where does the O in G3P come from?

Where does the ADP & NADP+ go?

Where does the G3P go?

CO2

From H2O via NADPH

CO2

Back to light reaction to recharge

Used to make glucose and other organic molecules

STOMA (pl. STOMATA)

http://www.cbu.edu/~seisen/Stomata.jpg

GUARD CELLS

PROBLEMS ON HOT DRY DAYS• If stomata are open to receive CO2 . . .

results in water loss

• On hot, dry days if plant shuts stomata to conserve water . . . photosynthesis slows

http://www.ipm.iastate.edu/ipm/icm/files/images/spider-mite-field.jpg

____ plants (Ex: rice, wheat, soybeans)(1st product of carbon fixation has 3 C’s- 3PG)

On hot, dry days when plant shuts stomata plant switches to ______________________Rubisco adds O2 to Calvin cycle instead of CO2

Product broken down by mitochondria/peroxisomes to release CO2

COUNTERPRODUCTIVE:Makes NO ATP Makes NO sugarUses ATPDecreases photosynthesis by siphoning

molecules from Calvin cycle

PHOTORESPIRATION

C3

ALTERNATIVE METHODS of CARBON FIXATION

• ______ plants(Ex: corn & sugarcane

• ______ Crassulacean acid metabolism(Ex: succulents, cactus, pineapple,)

WAYS TO AVOID DECREASE IN PHOTOSYNTHESIS DUE TO PHOTORESPIRATION

C4

CAM

SEE ANIMATION

CALVIN CYCLE found in BUNDLE SHEATH CELLS in C4 plants

*

________________________adds CO2 to make a 4 carbonmolecule before enteringCalvin Cycle

PEP CARBOXYLASE

5656

Process of using H+ gradient to generate ATP

= ________________________

(Can refer to ATP made in mitochondria too)

Process of creating ATP using a Proton gradient created by the

energy gathered from sunlight.

= ________________________

Process that consumes oxygen, releases CO2, generates no

ATP, and decreases photosynthetic output; generally occurs

on hot, dry, bright days, when stomata close and the oxygen

concentration in the leaf exceeds that of carbon dioxide

= ___________________________________

chemiosmosis

photophosphorylation

photorespiration