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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!!!