PHOTOSYNTHESISPHOTOSYNTHESIS

Providing Energy for LifeProviding Energy for Life

Do you remember food web Do you remember food web terminology?terminology?

Autotrophs = producersAutotrophs = producers PhotoautotrophsPhotoautotrophs ChemoautotrophsChemoautotrophs

Heterotrophs = consumersHeterotrophs = consumers Primary consumers, secondary consumers, etcPrimary consumers, secondary consumers, etc decomposersdecomposers

PhotosynthesisPhotosynthesis

Photoautotrophic cells contain pigments that Photoautotrophic cells contain pigments that absorb visible lightabsorb visible light This is their source of ENERGYThis is their source of ENERGY

Where does photosynthesis Where does photosynthesis occur?occur?

Leaf: cross sectionLeaf: cross section

PhotosynthesisPhotosynthesis

Most occurs in the mesophyll layer of the leafMost occurs in the mesophyll layer of the leaf Each mesophyll cell contains 30 - 40 chloroplastsEach mesophyll cell contains 30 - 40 chloroplasts

CHLOROPLASTCHLOROPLAST

CHLOROPLASTCHLOROPLAST

CHLOROPLASTCHLOROPLAST

CHLOROPLASTCHLOROPLAST

Light-absorbing pigments are embedded in Light-absorbing pigments are embedded in thylakoid membranesthylakoid membranes

A stack of thylakoids is called a A stack of thylakoids is called a granumgranum Plural = Plural = granagrana

Grana have a large surface area to allow Grana have a large surface area to allow greater diffusion of materialsgreater diffusion of materials

CHLOROPLASTCHLOROPLAST

STROMASTROMA Surrounds the thylakoid membranesSurrounds the thylakoid membranes Contains enzymes, DNA, RNAContains enzymes, DNA, RNA

Electromagnetic SpectrumElectromagnetic Spectrum

Electromagnetic spectrumElectromagnetic spectrum

Visible light drives photosynthesisVisible light drives photosynthesis Substances that absorb visible light are called Substances that absorb visible light are called

pigmentspigments Pigments appear different colors because they Pigments appear different colors because they

reflect different wavelengths (and thus absorb reflect different wavelengths (and thus absorb different wavelengths)different wavelengths)

Spectrophotometer measures the ability of a Spectrophotometer measures the ability of a pigment to absorb different wavelengths of lightpigment to absorb different wavelengths of light

CHLOROPLAST PIGMENTSCHLOROPLAST PIGMENTS

CHLOROPHYLL = green pigmentCHLOROPHYLL = green pigment Two forms of chlorophyllTwo forms of chlorophyll

Chlorophyll aChlorophyll a Chlorophyll bChlorophyll b

Chlorophyll absorbs light energy in the Chlorophyll absorbs light energy in the violet/blue and orange/red rangesviolet/blue and orange/red ranges REFLECTS in the green rangeREFLECTS in the green range

ChlorophyllChlorophyll

The color that we see is the color that is The color that we see is the color that is REFLECTED, not absorbedREFLECTED, not absorbed Therefore, chlorophyll appears GREEN, because Therefore, chlorophyll appears GREEN, because

green wavelength light is reflectedgreen wavelength light is reflected

Other Pigments in ChloroplastsOther Pigments in Chloroplasts

Xanthophyll: yellowXanthophyll: yellow Carotene: orangeCarotene: orange Different colors indicate that they absorb (and Different colors indicate that they absorb (and

therefore reflect) energy at different therefore reflect) energy at different wavelengthswavelengths

Absorption SpectraAbsorption Spectra

Plant PigmentsPlant Pigments

Located in the thylakoid membraneLocated in the thylakoid membrane Absorption spectrum tells us which Absorption spectrum tells us which

wavelengths are absorbed bestwavelengths are absorbed best Why is this important? HINT: it has to do with Why is this important? HINT: it has to do with

amount of energy absorbed!amount of energy absorbed!

PHOTOSYNTHESISPHOTOSYNTHESISOverviewOverview

Photosynthesis involves 3 energy conversionsPhotosynthesis involves 3 energy conversions 1. 1. absorptionabsorption of light energy of light energy 2. 2. conversionconversion of light energy into chemical energy of light energy into chemical energy 3. 3. storagestorage of chemical energy as sugars (carbon- of chemical energy as sugars (carbon-

containing compounds)containing compounds)

Law of Conservation of EnergyLaw of Conservation of Energy

REMEMBER!!!REMEMBER!!!

Energy cannot be created or destroyed, only Energy cannot be created or destroyed, only converted into different formsconverted into different forms

PHOTOSYNTHESISPHOTOSYNTHESISoverall summaryoverall summary

KNOW THIS!!!!!KNOW THIS!!!!!

Carbon dioxide gas combines with water in Carbon dioxide gas combines with water in the presence of light energy and the presence of light energy and chlorophyll to form sugar and oxygen gaschlorophyll to form sugar and oxygen gas

PHOTOSYNTHESISPHOTOSYNTHESIS

PHOTOSYNTHESISPHOTOSYNTHESIS

Photosynthesis occurs in 2 groups of reactionsPhotosynthesis occurs in 2 groups of reactions LIGHT REACTIONSLIGHT REACTIONS CALVIN CYCLE OR DARK REACTIONSCALVIN CYCLE OR DARK REACTIONS

PHOTOSYNTHESISPHOTOSYNTHESIS

I’M NOT GONNA DENY IT….THIS IS I’M NOT GONNA DENY IT….THIS IS GOING TO INVOLVE GOING TO INVOLVE MEMORIZATION!!MEMORIZATION!!

LIGHT REACTIONSLIGHT REACTIONS

Pigment molecules in the thylakoids absorb Pigment molecules in the thylakoids absorb light energylight energy

Light energy is converted to short-lived Light energy is converted to short-lived chemical energy in carrier moleculeschemical energy in carrier molecules Conversion to chemical energy has to do with Conversion to chemical energy has to do with

transfer of transfer of electronselectrons from one molecule to anotherfrom one molecule to another Remember Remember Oxidation-ReductionOxidation-Reduction reactions???? reactions????

Light ReactionsLight Reactions

Light ReactionsLight Reactions

CALVIN CYCLECALVIN CYCLE

Energy molecules from the light reactions are Energy molecules from the light reactions are used to make sugarused to make sugar

Also known as the DARK REACTIONSAlso known as the DARK REACTIONS

Calvin CycleCalvin Cycle

PHOTOSYNTHESIS: SUMMARYPHOTOSYNTHESIS: SUMMARY

AssignmentAssignment

Define/describe a PHOTOSYSTEMDefine/describe a PHOTOSYSTEM Diagram (and label) the light reactions of Diagram (and label) the light reactions of

photosynthesisphotosynthesis Diagram the dark reaction of photosynthesisDiagram the dark reaction of photosynthesis