PhotosynthesisPhotosynthesis

A Study of Life’s ComplexitiesA Study of Life’s Complexities

Light DefinitionsLight Definitions

• Light behaves like a particleLight behaves like a particle– Photon – Discreet bundle of radiationPhoton – Discreet bundle of radiation

• Light behaves like a waveLight behaves like a wave

Properties of LightProperties of Light

• Absorbed:Absorbed:

• Reflected:Reflected:

• Transmitted:Transmitted:

Electromagnetic SpectrumElectromagnetic Spectrum

• See OverheadSee Overhead

Visible LightVisible Light

• In the electromagnetic spectrum, we can In the electromagnetic spectrum, we can only see the visible light portiononly see the visible light portion

• What color of light is reflected from an What color of light is reflected from an orange shirt?orange shirt?

• What color(s) of light are absorbed by an What color(s) of light are absorbed by an orange shirt?orange shirt?

Light and PrismsLight and Prisms

• When white light strikes a prism, the When white light strikes a prism, the wavelengths separate and we see all wavelengths separate and we see all the different colorsthe different colors

What is PhotosynthesisWhat is Photosynthesis

• The conversion of Light, Carbon The conversion of Light, Carbon Dioxide and water into GlucoseDioxide and water into Glucose

Carbon Dioxide

Water

Glucose

Oxygen

PigmentsPigments

• Chloroplasts contain several different Chloroplasts contain several different pigments that absorb and reflect pigments that absorb and reflect different wavelengths of lightdifferent wavelengths of light

Absorption SpectraAbsorption Spectra

PigmentsPigments

• Chlorophyll A: Absorbs mainly in the Chlorophyll A: Absorbs mainly in the violet and redviolet and red

• Chlorophyll B: Absorbs mainly in blue Chlorophyll B: Absorbs mainly in blue and orangeand orange

• Carotenoids: Absorb mainly in the Carotenoids: Absorb mainly in the green and bluegreen and blue

Closing QuestionsClosing Questions

• Why are there so many pigments?Why are there so many pigments?

• Why do plants appear green in the Why do plants appear green in the summer and change colors during summer and change colors during the fall?the fall?

The Nut’s and BoltsThe Nut’s and Bolts

Light Dependent

Light Independent

NADPH

ATP

NADP

ADP

Products of Light ReactionProducts of Light Reaction

• ATP (Adenosine Tri-Phosphate)ATP (Adenosine Tri-Phosphate)– Carries energy to dark reactionCarries energy to dark reaction– ADP (Di) is converted into ATP by ATP ADP (Di) is converted into ATP by ATP

synthasesynthase

• NADPH NADPH (Nicotinamide Adenine Dinucleotide (Nicotinamide Adenine Dinucleotide Phosphate)Phosphate)

– Carries electrons and protons (HCarries electrons and protons (H++) to dark ) to dark reactionreaction

Basics of PhotosynthesisBasics of Photosynthesis

• Photosynthesis occurs within the Photosynthesis occurs within the chloroplasts of plantschloroplasts of plants

Components of Light Components of Light ReactionReaction• 2 Photosystems: Collection of pigments2 Photosystems: Collection of pigments

– Photosystem II happens before PS IPhotosystem II happens before PS I– Hold chlorophyll and carotenoidsHold chlorophyll and carotenoids

• Electron Transport Chain (ETC)Electron Transport Chain (ETC)– Chain of molecules that pass down electronsChain of molecules that pass down electrons– The movement of electrons results in a The movement of electrons results in a

negative charge which propels H+ atoms negative charge which propels H+ atoms through the thylakoid membranethrough the thylakoid membrane

Light ReactionLight Reaction

PS 2 PS 1E T C

Electrons

• Sunlight strikes PS 2 and excite electrons that flow down the ETC

• The electrons cause a negative charge and propel H+ into the thylakoid

• Exhausted electrons reach PS 1 and get excited again by sunlight

• Excited electrons flow onto NADP NADP-

NADP

Light ReactionLight Reaction

PS 2 PS 1E T C

Water 2H+ + O + e-

Water splits in the thylakoid to form

2 Hydrogens (Accumulate in thylakoid)

1 Oxygen (Released into atmosphere)

2 Electrons (Pumped back into PS 2)

Light ReactionLight Reaction

PS 2 PS 1E T C

• Hydrogens accumulate in thylakoid and begin going through ATP Synthase

• ADP from dark reaction is turned into ATP with help of ATP Synthase

• ATP travels to Dark Reaction carrying Energy

H+

ADP

ATP

Light ReactionLight Reaction

PS 2 PS 1E T C

• The negatively charged NADP picks up a proton and becomes NADPH

• NADPH carries electrons and protons to the dark reaction

NADP- NADPHH+

Light Reaction: 2 ChoicesLight Reaction: 2 Choices

Deals with the path the electrons takeDeals with the path the electrons take– Non-cyclic PathwayNon-cyclic Pathway

•PS II PS II ETC ETC PS I PS I NADPH NADPH

•Results: NADPH + ATPResults: NADPH + ATP

– Cyclic PathwayCyclic Pathway•PS II PS II ETC ETC Back to PS II Back to PS II

•Results: ATP but NO NADPHResults: ATP but NO NADPH– No Dark reactionNo Dark reaction

The Dark ReactionThe Dark Reaction

• Does not require LightDoes not require Light

• Also known as the Calvin CycleAlso known as the Calvin Cycle

• Occurs within the stroma of the Occurs within the stroma of the chloroplastschloroplasts

• Uses NADPH and ATP from light Uses NADPH and ATP from light reaction and COreaction and CO22 from the atmosphere from the atmosphere to create GLUCOSEto create GLUCOSE

The Dark Reaction: Calvin The Dark Reaction: Calvin CycleCycle

• RuBP – Ribulose Bis-Phosphate (4C’s)RuBP – Ribulose Bis-Phosphate (4C’s)

• PGA – Phosphoglyceric Acid (3C’s)PGA – Phosphoglyceric Acid (3C’s)

• PGAL or G3P– Phosphoglyceraldehide PGAL or G3P– Phosphoglyceraldehide (3C’s)(3C’s)

• Glucose – 6C’sGlucose – 6C’s

• It takes 6 turns of the cycle to form It takes 6 turns of the cycle to form one glucoseone glucose

Leaf StructureLeaf Structure

The Calvin CycleThe Calvin Cycle

But how does carbon dioxide get into the cycle???

Problems with the Dark Problems with the Dark ReactionReaction

• RUBISCO – Can bond to CO2 or OxygenRUBISCO – Can bond to CO2 or Oxygen– Ribulose Bisphosphate Carboxylase Ribulose Bisphosphate Carboxylase

OxygenaseOxygenase

• If RUBISCO bonds to Carbon Dioxide:If RUBISCO bonds to Carbon Dioxide:– Photosynthesis occurs – Glucose is madePhotosynthesis occurs – Glucose is made

• If RUBISCO bonds to OxygenIf RUBISCO bonds to Oxygen– Photorespiration occurs – Glucose is Photorespiration occurs – Glucose is

broken down to make energybroken down to make energy

Other Problems that may Other Problems that may occuroccur

• Some plants live in hot climates and Some plants live in hot climates and must close their stomates during the must close their stomates during the dayday– Why?Why?

– How does this affect the plant How does this affect the plant negatively?negatively?

Photosynthetic PathwaysPhotosynthetic Pathways

• C3 pathwayC3 pathway

• C4 pathway – Separation based on distanceC4 pathway – Separation based on distance

• CAM pathway – Separation based on timeCAM pathway – Separation based on time

• All have their benefits, all have their All have their benefits, all have their limitationslimitations

C3 PlantsC3 Plants

• Type of climate:Type of climate:

• Stomate strategy:Stomate strategy:

• Photorespiration strategy:Photorespiration strategy:

• Type of PlantsType of Plants

C4 Plants – Separation C4 Plants – Separation based on Distancebased on Distance

C4 PlantsC4 Plants

• Type of climate:Type of climate:

• Stomate strategy:Stomate strategy:

• Photorespiration strategy:Photorespiration strategy:

• Type of PlantsType of Plants

CAM Plants – Separation CAM Plants – Separation Based on TimeBased on Time

CAM PlantsCAM Plants

• Type of climate:Type of climate:

• Stomate strategy:Stomate strategy:

• Photorespiration strategy:Photorespiration strategy:

• Type of PlantsType of Plants