PhotosynthesisBy: Matt Goebel, Julia Douglas,

Brandon Schroeder, and Courtney Rodgers

Structure of Chloroplasts

•Chloroplast envelope: double membrane

•Internal membranes→ Tykaloids

•Stroma: clear fluid around tykaloids

•Grana: stacks of tykaloids

Photosynthesis

•Light energy into chemical energy–Occurs in Chloroplasts (or prokaryotic equivalent)

•Light from sun has range of wavelengths-Different colors

Photosynthesis•Chlorophyll are the main photosynthetic pigment

–Light is trapped here–Embedded in the Chloroplast’s membrane

•Different colors, different absorption from chlorophyll

•Remaining colors reflected back

‒ green leaves

AbsorptionAll chlorophyll absorb red & blue

Measured in Photons‒Pigment absorbs photon through electrons‒Too much energy/ not enough energy and the energy

can't be absorbed‒Electron at high energy level is called an excited

electron

Accessory pigments absorb other wavelengths and then transfers them to chlorophyll

Action Spectrum

• Rate of absorption

Absorption Spectra

• % of absorbancy

Photosynthesis

•Light energy used to produce ATP and split water molecule

–Light captured by Chlorophyll–Light energy trapped into Chemical energy (electrons)–Chemical energy used to form ATP–Split water molecule used for:

•Organic molecules (Ex. Glucose)•Oxygen given off

Photosynthesis

•Hydrogen combined with carbon dioxide used to form organic compounds (Ex. Sugar)

–Bonds formed by energy from ATP–Different combinations of C, H, O and N–Plants are able to form all the organic compounds they need

Photosynthesis

•Photosynthesis can be measured by:–Depletion of substrate

•Because: rate of photosynthesis changes, the measure of water/carbon dioxide being used changes

–Increase in biomass•Because: rate of photosynthesis changes, rate of organic molecules created change, biomass change

Photosynthesis

•Factors affecting photosynthesis:–Temperature–Light Intensity–Carbon Dioxide Concentration

•Temperature affects photosynthesis–Increases with kinetic energy of reactants–Maximum at “optimal” temperature–Decreases as enzymes begin to denature

Photosynthesis•Carbon Dioxide Concentration

–As the CO2 increases, so does the reaction–Maximum rate of photosynthesis is reached–Saturation point with CO2 is met and no longer affects plant’s rate of photosynthesis

Photosynthesis

•Light Intensity–At low levels, photosynthesis cant occur at high rate–Increase in light intensity, increase rate of photosynthesis–Light intensity keeps increasing until rate of photosynthesis can’t increase anymore–Too high intensity can damage cell

Limiting Factors

•Only 1 factor actually limits photosynthesis

–Factor furthest from optimum

•Factors:

–Light intensity

–Carbon Dioxide concentration

– Temperature

Light-dependent reactions

Light-dependent reactions MUST have light 2 parts:

1) Photosystem II 2) Photosystem I

Photosystem II• Electron acceptor: accepts excited electrons

from chlorophyll

‒ Plastoquinne (hydrophobic)

• Accepts 2 electrons and becomes reduced plastoquinne

• Causes photolysis of water

‒ Generates Oxygen

• Reduced plastoquinne has energy for photosynthesis

Photophoshorylation & Chemiosmosis

• Photophoshorylation

‒ ATP from light energy

‒ Main = non-cyclic

‒ Energy pumps proteins across tykaloid membrane

• Chemiosmosis

‒ Proteins travel back over gradient

‒ ATP becomes ADP

‒ Plastocyanin takes electrons

Photosystem I

• Product is NADPH

• Electrons are photoactivated

– Electrons are passed along chain of freedoxin (protein)

• Electron from photosystem I replaced by electrons from plastocyanin

– Used to reduce NADP

• Electrons move back up chain → ATP

Light-Independent Reactions

• Don’t use light

• Calvin cycle

‒ Occurs in stroma

‒ Uses excited electrons

‒ Carbon dioxide and water to organic compounds

‒ Produces: glyceraldehyde-3-phosphate, 3 ADP, and 2 NADP+

Light-Independent Reactions

Have a nice day!!!