Photosynthesis

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6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O

C18O2

Hypothesis: If H2O is being oxidized

H218O

18O

Can you predict where the heavy oxygen will end up in each case?

6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O

18O

18O Isotope Experiment

Slide 10

6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O

C18O2

H218O

18O

6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O

18O

The Actual Results!!

So it’s the water that’s being oxidized!

Slide 11

6 CO2

12 H2O

Reactants

Products

C6H12O6 6H2O 6O2

Tracking Atoms in Photosynthesis

Slide 12

What does this suggest about photosynthesis?

6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O

The sugars that result from photosynthesis are produced by adding the hydrogen ions and electrons from water to carbon dioxide, NOT by splitting CO2 and adding water!

oxidized

reduced

H+ and e-

Slide 13

internal leaf structure

chloroplasts

outer membrane

inner membrane

thylakoid

Plant Photosynthesis

Slide 14

The stages of photosynthesis

Light Dependent Reactions

Occurs along the thylakoid membrane

this is where H2O is oxidized.

chemiosmotic production of ATP!

electron carrier (NADPH) is synthesized

Slide 15

Light Independent Reactions

Occurs in the stroma of the chloroplast.

Where CO2 is “fixed” into sugars!

The stages of photosynthesis…

Slide 16

How plants harness energy from sunlight

Photosynthetic pigments

Chlorophylls a – the “main” photosynthetic pigment

Chlorophyll b

Accessory pigments

Carotenoids

Slide 17

Photosynthetic pigments are arranged as “photosystems”

Slide 18

What wavelengths of light do you think plants use the least in photosynthesis?

Slide 19

Photosystems use some wavelengths of light but reflect others…

Slide 20

Light Harvesting Pigments

Reaction Center

Photon

Photosystem

From the Photosystem, e- are passed along an Electron Transport Chain The Photosynthetic Electron Transport Chain (PETC)