Photosynthesis
I. Introduction
A. Goal of photosynthesis
To construct food using light energy
Food = Glucose
Converting radient energy (sun) to
Chemical energy.
I. Introduction
B. Photosynthetic organisms
Called Autotrophs
Examples – Plants, Algae
II. The Physics of LightA. Light travels in wave
Wavelength – distance peak to peak
Frequency – height of wave
II. The Physics of LightB. Visible Light
spectrum
II. The Physics of Light
C. Energy in light
Highest energy =
Short wavelength
High frequency
III. Photosynthesis and Pigments
A. Pigments absorb some colors and reflect others
1. Reflected colors is what we see
III. Photosynthesis and Pigments
A. Pigments absorb some colors and reflect others
2. Absorbed colors raises electrons to higher energy levels – generates heat
III. Photosynthesis and PigmentsB. Pigments in plants
1. Chlorophyll A – absorbs from ends of visible spectrum
2. Chlorophyll B – absorbs toward the middle of the spectrum
III. Photosynthesis and PigmentsB. Pigments in plants
3. Carotenoids – Aid Chlorophyll.
Orange and yellow in color
III. Photosynthesis and PigmentsC. Chloroplast structure
Double membrane
Filled with dense solution – Stroma
Thylakoid membranes
Thylakoids stack up = Grana (granum)
III. Photosynthesis and PigmentsC. Chloroplast structure
III. Photosynthesis and PigmentsD. Chloroplasts – locations
Green areas – mainly leaves
IV. Photosynthesis ProcessA. Two parts
1. Light Reactions (Sun necessary)Goal – convert sun energy to
chemical energy2. Dark Reactions (No light needed)
Goal – Build Glucose
IV. Photosynthesis ProcessB. The Light Reaction
1. Photosystem 2Pigments receive sun energyElectrons are raised to high energy level
Electrons passed down anElectron transport chain,
loosing energy as they goElectron Energy used to convert
ADP to ATPElectrons are passed to next step
Lost electrons are replaced by splitting water
IV. Photosynthesis ProcessB. The Light Reaction
2. Photosystem 1Receives electrons from P2Electrons energized by sunTwo directions for electrons
a. Non-cyclic flowElectrons become part of
NADPH (Chem. Energy)
IV. Photosynthesis ProcessB. The Light Reaction2. Photosystem 1Two directions for electons
b. Cyclic flowEnergized Electrons Make H move through enzymeATP SynthaseMakes lots of ATP!Used electrons cycle back
IV. Photosynthesis ProcessB. The Light ReactionSummary of light reactions
Photosystem 2Sends ATP energy to Dark Reactions
Photosystem 1 Non-cyclic – Sends NADPH to Dark R.
(High energy electron carrier) Cyclic – Sends ATP to Dark Reactions
Key – Light reactions convert sun energy tochemical energy to power the dark reactions
IV. Photosynthesis ProcessB. The Dark Reactions
Called the Calvin Cycle
This is the “Glucose Machine”
Powered by ATP and NADPH from
the light reactions
CO2 provides carbon to make Glucose
Oxygen is the waste product
(Given off from light reaction)