Exercise 6:Exercise 6:PhotosynthesisPhotosynthesis

Questions that will be addressed:Questions that will be addressed:

• Where does the carbon that organic molecules Where does the carbon that organic molecules are made of come from?are made of come from?

• Where does the energy that drives the Where does the energy that drives the synthesis of organic molecules come from? synthesis of organic molecules come from?

The answers vary, depending on the The answers vary, depending on the organismorganism

• Autotrophs – Self-nourishingAutotrophs – Self-nourishing– Photoautotrophs – Carbon source is COPhotoautotrophs – Carbon source is CO22 from the from the

air and sunlight is the energy source that drives air and sunlight is the energy source that drives synthesis.synthesis.

• Heterotrophs – Feed on autotrophs.Heterotrophs – Feed on autotrophs.

PhotoautotrophsPhotoautotrophs

• Plants, some bacteria, and many protistans are Plants, some bacteria, and many protistans are photoautotrophs.photoautotrophs.– Photoautotrophs synthesize organic molecules Photoautotrophs synthesize organic molecules

from COfrom CO22 by a process called Photosynthesis. by a process called Photosynthesis.

– Photosynthesis: energy form the sun is used to Photosynthesis: energy form the sun is used to drive synthesis.drive synthesis.

Overview of PhotosynthesisOverview of Photosynthesis

12H2O + 6CO2 6O2 + C6H12O6 + 6H2O

Glucose

Sucrose, Starch, or Cellulose

Photosynthesis Occurs in Two StagesPhotosynthesis Occurs in Two Stages

• 1. 1. Light-Dependent ReactionsLight-Dependent Reactions – Split water – Split water and generate ATP and NADPHand generate ATP and NADPH– Occur in the Thylakoid Membrane of ChloroplastOccur in the Thylakoid Membrane of Chloroplast

• 2. 2. Light-Independent ReactionsLight-Independent Reactions – Use the – Use the ATP and NADPH generated in the Light-ATP and NADPH generated in the Light-Dependent reactions to make Glucose.Dependent reactions to make Glucose.– Occur in the Stroma of ChloroplastOccur in the Stroma of Chloroplast

The Light-Dependent ReactionsThe Light-Dependent Reactions

• Photoautotrophs use pigments to absorb Photoautotrophs use pigments to absorb sunlight energy.sunlight energy.

• This energy is then used to drive This energy is then used to drive photosynthesis.photosynthesis.

Properties of Light cont’dProperties of Light cont’d

• Visible light is in the Visible light is in the range of 400-700 nm. range of 400-700 nm.

• People and other organisms see the different People and other organisms see the different s as different colors.s as different colors.

Wavelength of light (nanometers)

Light as particlesLight as particles

• The energy of light is absorbed as if it is organized The energy of light is absorbed as if it is organized into packets. These packets are called into packets. These packets are called PhotonsPhotons..– Each type of photon has a fixed amount of energy Each type of photon has a fixed amount of energy

characterized by its wavelength.characterized by its wavelength.• Pigments are molecules that absorb photons.Pigments are molecules that absorb photons.

– Most pigments only absorb some wavelengths of light and Most pigments only absorb some wavelengths of light and transmit (reflect) others. The wavelengths that are transmit (reflect) others. The wavelengths that are transmitted, determine what color an object appears.transmitted, determine what color an object appears.

– A pigment that A pigment that absorbsabsorbs all wavelengths of visible light all wavelengths of visible light appears appears blackblack..

– A pigment that A pigment that reflectsreflects all wavelengths of visible light all wavelengths of visible light appear appear whitewhite..

PigmentsPigments

• Chlorophylls are the primary pigments in most Chlorophylls are the primary pigments in most photoautotrophs.photoautotrophs.– Chlorophyll Chlorophyll aa – mostly absorb red and blue light. – mostly absorb red and blue light.– Chlorophyll Chlorophyll bb – absorbs blue and red-orange light. – absorbs blue and red-orange light.

• Carotenoids, Xanthophylls, anthocyanins, and Carotenoids, Xanthophylls, anthocyanins, and phycobilins are accessory pigments found in phycobilins are accessory pigments found in photoautotrophs.photoautotrophs.– They absorb wavelengths that chlorophylls miss, blue-They absorb wavelengths that chlorophylls miss, blue-

violet and blue-green. They reflect red, orange, and violet and blue-green. They reflect red, orange, and yellow.yellow.

Absorption SpectrumAbsorption Spectrum

per

cen

t o

f w

avel

eng

ths

abso

rbed

per

cen

t o

f w

avel

eng

ths

abso

rbed

wavelengths (nanometers)wavelengths (nanometers)

chlorophyll b

chlorophyll a

beta-carotenephycoerythrin (a phycobilin)

Absorption SpectrumAbsorption Spectrum

chlorophyll b

chlorophyll a

carotenoids

phycoerythrin (a phycobilin)

(combined absorption efficiency across entire visible spectrum)

chlorophyll a

chlorophyll b

Phycocyanin(a phycobilin)

Plant PigmentPlant PigmentPaper ChromatographyPaper Chromatography

• Chromatography is the separation of Chromatography is the separation of molecules in a mixture based on their molecules in a mixture based on their solubility in a particular solvent and their solubility in a particular solvent and their interaction with the chromatography interaction with the chromatography matrix.matrix.

• Pigments:Pigments:– Chlorophyll a, Chlorophyll b, Beta-carotenes, Chlorophyll a, Chlorophyll b, Beta-carotenes,

and Xanthophylls.and Xanthophylls.• Solvent: Petroleum Ether and Acetone are Solvent: Petroleum Ether and Acetone are

non-polar solvents.non-polar solvents.• The most non-polar pigments will travel The most non-polar pigments will travel

further up the paper while the polar further up the paper while the polar pigments will not travel as far.pigments will not travel as far.

Plant Pigment Plant Pigment Paper ChromatographyPaper Chromatography

Beta-Carotene

Xanthophylls

Chlorophyll a

Chlorophyll b

Ratio Factor (Rf) =Distance pigment moved

Distance solvent moved

Measuring Photosynthesis in ElodeaMeasuring Photosynthesis in Elodea

• We will measure photosynthesis in Elodea We will measure photosynthesis in Elodea under different light conditions.under different light conditions.– White light – Oxygen Production White light – Oxygen Production

– No light – Oxygen ConsumptionNo light – Oxygen Consumption

– Green light – Oxygen ProductionGreen light – Oxygen Production

White LightWhite Light

12H2O + 6CO2 6O2 + C6H12O6 + 6H2O

RespirationPhotosynthesis

Net Photosynthesis

Absorption SpectrumAbsorption Spectrum

chlorophyll b

chlorophyll a

carotenoids

phycoerythrin (a phycobilin)

(combined absorption efficiency across entire visible spectrum)

chlorophyll a

chlorophyll b

Phycocyanin(a phycobilin)

No LightNo Light

12H2O + 6CO2 6O2 + C6H12O6 + 6H2O

RespirationPhotosynthesis

XX

Net Photosynthesis + Respiration = Gross Photosynthesis

Green LightGreen Light

12H2O + 6CO2 6O2 + C6H12O6 + 6H2O

RespirationPhotosynthesis

X

X

Net Photosynthesis

Absorption SpectrumAbsorption Spectrum

chlorophyll b

chlorophyll a

carotenoids

phycoerythrin (a phycobilin)

(combined absorption efficiency across entire visible spectrum)

chlorophyll a

chlorophyll b

Phycocyanin(a phycobilin)

No Green LightNo Green Light

12H2O + 6CO2 6O2 + C6H12O6 + 6H2O

RespirationPhotosynthesis

XX

Net Photosynthesis + Respiration = Gross Photosynthesis

COCO22 Uptake Uptake

H2O + CO2 HCO2 + -OHCarbonic Acid