Photosynthesis

• Almost all plants are photosynthetic autotrophs, as are some bacteria and protists– Autotrophs generate their own organic matter

through photosynthesis– Sunlight is transformed to energy stored in the

form of chemical bonds

(a) Mosses, ferns, andflowering plants

(b) Kelp

(c) Euglena (d) Cyanobacteria

THE BASICS OF PHOTOSYNTHESIS

Why is Photosynthesis important?

Makes organic molecules (glucose) out of inorganic materials (carbon dioxide and water).It begins all food chains/webs. Thus all life is supported by this process.It also makes oxygen gas!!

Photosynthesis-starts to ecological food webs!

WHY ARE PLANTS GREEN?

It's not that easy bein' green Having to spend each day the color of the leaves When I think it could be nicer being red or yellow or gold Or something much more colorful like that…

Kermit the Frog

Electromagnetic Spectrum and Visible Light

Gammarays X-rays UV

Infrared & Microwaves Radio waves

Visible light

Wavelength (nm)

Different wavelengths of visible light are seen by the human eye as different colors.

WHY ARE PLANTS GREEN?

Gammarays

X-rays UV Infrared Micro-waves

Radiowaves

Visible light

Wavelength (nm)

Sunlight minus absorbed wavelengths or colors equals the apparent color of an object.

The feathers of male cardinals are loaded with carotenoid pigments. These pigments absorb some wavelengths of light and reflect others.

Reflected light

Why are plants green?

Reflected lig

ht

Transmitted light

WHY ARE PLANTS GREEN?

Plant Cells have Green Chloroplasts

The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).

• Chloroplasts absorb light energy and convert it to chemical energy

LightReflected

light

Absorbedlight

Transmittedlight

Chloroplast

THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED

Plants use sunlight to turn water and carbon dioxide into glucose. Glucose is a kind of sugar. Plants use glucose as food for energy and as a building block for growing.Autotrophs make glucose and heterotrophs are consumers of it.

Photo-synthesismeans "putting together with light."

PHOTOSYNTHESIS

• Absorbing Light Energy to make chemical energy: glucose!– Pigments: Absorb different colors of

white light (ROY G BIV)• Main pigment: Chlorophyll a• Accessory pigments: Chlorophyll b and

Carotenoids• These pigments absorb all wavelengths

(light) BUT not green!

Chloroplasts: Sites of Photosynthesis

• Photosynthesis– Occurs in chloroplasts, organelles in certain

plants– All green plant parts have chloroplasts and carry

out photosynthesis• The leaves have the most chloroplasts• The green color comes from chlorophyll in the

chloroplasts• The pigments absorb light energy

• In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts

• A chloroplast contains: – stroma, a fluid – grana, stacks of thylakoids

• The thylakoids contain chlorophyll– Chlorophyll is the green pigment that captures

light for photosynthesis

Photosynthesis occurs in chloroplasts

• The location and structure of chloroplasts

LEAF CROSS SECTIONMESOPHYLL CELL

LEAF

Chloroplast

Mesophyll

CHLOROPLAST Intermembrane space

Outermembrane

Innermembrane

ThylakoidcompartmentThylakoidStroma

Granum

StromaGrana

• Chloroplasts contain several pigmentsChloroplast Pigments

– Chlorophyll a – Chlorophyll b – Carotenoids

Figure 7.7

Chlorophyll a & b• Chl a has a methyl

group • Chl b has a carbonyl

group

Porphyrin ring delocalized e-

Phytol tail

Different pigments absorb light differently

Excitedstate

e

Heat

Light

Photon

Light(fluorescence)

Chlorophyllmolecule

Groundstate

2

(a) Absorption of a photon

(b) fluorescence of isolated chlorophyll in solution

Excitation of chlorophyll in a chloroplast

Loss of energy due to heat causes the photons of light to be less energetic.

Less energy translates into longer wavelength.

Energy = (Planck’s constant) x (velocity of light)/(wavelength of light)

Transition toward the red end of the visible spectrum.

e

Fall Colors

• During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments.

• Carotenoids are pigments that are either red or yellow.

Chlorophyll: A Light Absorbing PigmentThe Solar Panel Chemical!

Photosynthesis

Glucose provides the energy and carbon needed to make other plant materials like wax and proteins.

• Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water

AN OVERVIEW OF PHOTOSYNTHESIS

Carbondioxide

Water Glucose Oxygengas

PHOTOSYNTHESIS

• The Calvin cycle makes sugar from carbon dioxide– ATP generated by the light

reactions provides the energy for sugar synthesis

– The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose

LightChloroplast

Lightreactions

Calvincycle

NADP

ADP+ P

• The light reactions convert solar energy to chemical energy– Produce ATP &

NADPH

AN OVERVIEW OF PHOTOSYNTHESIS

Oxygen and Sugar!

• In plants and simple animals, waste products are removed by diffusion. Plants, for example, excrete O2, a product of photosynthesis.

EQUATION FOR PHOTOSYNTHESIS

6CO2 + 6H2O + ENERGY C6H12O6 + 6O2

CARBON DIOXIDE

WATER

GLUCOSE

OXYGEN

Redox Reaction

• The transfer of one or more electrons from one reactant to another.

• Two types:

1. Oxidation

2. Reduction

Oxidation Reaction

• The loss of electrons from a substance.• Or the gain of oxygen.

glucose

6CO2 + 6H2O C6H12O6 + 6O2

Oxidation

Reduction Reaction

• The gain of electrons to a substance.• Or the loss of oxygen.

glucose

6CO2 + 6H2O C6H12O6 + 6O2

Reduction

PHOTOSYNTHESIS• 2 Phases

– Light-dependent reaction– Light-independent reaction

• Light-dependent: converts light energy into chemical energy; produces ATP and NADPH molecules to be used to fuel light-independent reaction

• Light-independent: uses ATP produced to make simple sugars/ glucose

PHOTOSYNTHESIS• Light-dependent reaction (LIGHT

Reaction)– Requires light– Occurs in chloroplast (in thylakoids)– Chlorophyll (thylakoid) traps energy from

light– Light excites electron (e-)

• Kicks e- out of chlorophyll to an electron transport chain

• Electron transport chain: series of proteins in thylakoid membrane

– Bucket brigade

PHOTOSYNTHESIS• Light-dependent reaction (LIGHT

Reaction)– Energy lost along electron transport

chain– Lost energy used to recharge ATP from

ADP

– NADPH produced from e- transport chain• Stores energy until transfer to stroma• Plays important role in light-independent

reaction

– Total byproducts: ATP, NADP, O2

1. Light Reaction (Electron Flow)

• During the light reaction, there are two possible routes for electron flow.

A. Cyclic Electron Flow

B. Noncyclic Electron Flow

Ph

oto

n

Ph

oto

n

Water-splittingphotosystem

NADPH-producingphotosystem

ATPmill

• Two types of photosystems cooperate in the light reactions

A. Cyclic Electron Flow

• Occurs in the thylakoid membrane.• Uses Photosystem I only• P700 reaction center- chlorophyll a • Uses Electron Transport Chain (ETC)• Generates ATP only

ADP + ATPP

A. Cyclic Electron Flow

P700

PrimaryElectronAcceptor

e-

e-

e-

e-

ATPproducedby ETC

Photosystem I

AccessoryPigments

SUN

Photons

B. Noncyclic Electron Flow

• Occurs in the thylakoid membrane

• Uses PS II and PS I

• P680 rxn center (PSII) - chlorophyll a

• P700 rxn center (PS I) - chlorophyll a

• Uses Electron Transport Chain (ETC)

• Generates O2, ATP and NADPH

B. Noncyclic Electron Flow

P700

Photosystem IP680

Photosystem II

PrimaryElectronAcceptor

PrimaryElectronAcceptor

ETC

EnzymeReaction

H2O

1/2O2 + 2H+

ATP

NADPH

Photon

2e-

2e-

2e-

2e-

2e-

SUN

Photon

B. Noncyclic Electron Flow

• ADP + ATP

• NADP+ + H NADPH

• Oxygen comes from the splitting of H2O, not CO2

H2O 1/2 O2 + 2H+

(Reduced)

P(Reduced)

(Oxidized)

Primaryelectron acceptor

Primaryelectron acceptor

Electron transport chain

Electron transport

Photons

PHOTOSYSTEM I

PHOTOSYSTEM II

Energy forsynthesis of

by chemiosmosis

Noncyclic Photophosphorylation • Photosystem II regains electrons by splitting

water, leaving O2 gas as a by-product

• The O2 liberated by photosynthesis is made from the oxygen in water (H+ and e-)

Plants produce O2 gas by splitting H2O

2 H + 1/2

Water-splittingphotosystem

Reaction-center

chlorophyll

Light

Primaryelectronacceptor

Energyto make

Electron transport chain

Primaryelectronacceptor

Primaryelectronacceptor

NADPH-producingphotosystem

Light

NADP

1

23

How the Light Reactions Generate ATP and NADPH

Chemiosmosis

• Powers ATP synthesis.

• Located in the thylakoid membranes.

• Uses ETC and ATP synthase (enzyme) to make ATP.

• Photophosphorylation: addition of phosphate to ADP to make ATP.

ChemiosmosisH+ H+

ATP Synthase

H+ H+ H+ H+

H+ H+high H+

concentration

H+ADP + P ATP

PS II PS IE

TC

low H+

concentration

H+

ThylakoidSpace

Thylakoid

SUN (Proton Pumping)

• The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H+ through that membrane– The flow of H+ back through the membrane is

harnessed by ATP synthase to make ATP– In the stroma, the H+ ions combine with NADP+

to form NADPH

Chemiosmosis powers ATP synthesis in the light reactions

• The production of ATP by chemiosmosis in photosynthesis

Thylakoidcompartment(high H+)

Thylakoidmembrane

Stroma(low H+)

Light

Antennamolecules

Light

ELECTRON TRANSPORT CHAIN

PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

PHOTOSYNTHESIS• Light-independent reaction (Dark

Reaction)– Does not require light– Calvin Cycle

• Occurs in stroma of chloroplast• Requires CO2

• Uses ATP and NADPH as fuel to run• Makes glucose sugar from CO2 and Hydrogen

Calvin Cycle

• Carbon Fixation (light independent rxn).

• C3 plants (80% of plants on earth).

• Occurs in the stroma.

• Uses ATP and NADPH from light rxn.

• Uses CO2.

• To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.

Chloroplast

GranumThylakoid

Stroma

Outer Membrane

Inner Membrane

• A Photosynthesis Road Map

Chloroplast

Light

Stack ofthylakoids ADP

+ P

NADP

Stroma

Lightreactions

Calvincycle

Sugar used for

Cellular respiration Cellulose

Starch

Other organic compounds

PHOTOSYNTHESIS• What affects photosynthesis?

– Light intensity: as light increases, rate of photosynthesis increases

PHOTOSYNTHESIS• What affects photosynthesis?

– Carbon Dioxide: As CO2 increases, rate of photosynthesis increases

PHOTOSYNTHESIS• What affects photosynthesis?

– Temperature: • Temperature Low = Rate of photosynthesis

low• Temperature Increases = Rate of

photosynthesis increases• If temperature too hot, rate drops

Photorespiration

• Occurs on hot, dry, bright days.

• Stomates close.

• Fixation of O2 instead of CO2.

• Produces 2-C molecules instead of 3-C sugar molecules.

• Produces no sugar molecules or no ATP.

Photorespiration

• Because of photorespiration: Plants have special adaptations to limit the effect of photorespiration.

1. C4 plants

2. CAM plants

C4 Plants

• Hot, moist environments.

• 15% of plants (grasses, corn, sugarcane).

• Divides photosynthesis spatially.

• Light rxn - mesophyll cells.

• Calvin cycle - bundle sheath cells.

C4 Plants

Mesophyll Cell

CO2

C-C-C

PEP

C-C-C-CMalate

ATP

Bundle Sheath Cell

C-C-C

Pyruvic Acid

C-C-C-C

CO2

C3

Malate

Transported

glucoseVascular Tissue

CAM Plants

• Hot, dry environments.

• 5% of plants (cactus and ice plants).

• Stomates closed during day.

• Stomates open during the night.

• Light rxn - occurs during the day.

• Calvin Cycle - occurs when CO2 is present.

CAM PlantsNight (Stomates Open) Day (Stomates Closed)

Vacuole

C-C-C-C

Malate

C-C-C-C

Malate Malate

C-C-C-CCO2

CO2

C3

C-C-CPyruvic acid

ATPC-C-C

PEP glucose

Check it!

1. The process that uses the sun’s energy to make simple sugars is _____________.

A. Cellular respiration

B. Glycolysis

C. Photosynthesis

D. Photolysis

Check it!

2. The function accomplished by the light-dependent reactions is ______________.

A. Energy storage

B. Sugar production

C. Carbon fixation

D. Conversion of sugar