Ch 10 Photosynthesis

Photosynthesis

• plants harnessing the energy in sunlight to create sugar

• redox reaction

  • CO2 reduced to C6H12O6

  • H2O oxidized to O2

• anabolic (builds sugar), endergonic, requires energy

• takes place in chloroplasts

Chloroplast Structure

• outer membrane

• inter-membrane space

• inner membrane

• stroma (like mitochondrial matrix)

  • where Calvin cycle occurs

• granum (stacks of thylakoid)

• thylakoid (membranous system stacked in columns)

• thylakoid membrane

  • where light reaction occurs

  • photosystems located here

• thylakoid space

Sunlight

solar energy in the form of electromagnetic waves

• photons of light traveling in a wave

Wavelength range that visible light falls in

380 - 750 nm (ROY G BIV)

Photosynthetic Pigments

• contained by plants

• each pigment absorbs light of a different wavelength

• each pigment reflects light that is not used for photosynthesis (ex. green)

Chlorophyll a

• dark green

• peak absorption around 430 nm and 680 nm

Chlorophyll b

• light green

• peak absorption around 450 nm & 650 nm

Carotenoids

• orange

• peak absorption is narrow range of 480 nm - 500 nm

Photosynthesis Equation

light energy + 6CO2 + H2O → C6H12O6 +6O2

Chlorophyll Excitation

when a molecule of chlorophyll absorbs a photon of light, it goes from a stable state to an excited state

• individual electrons in the chlorophyll absorb the light energy causing the electron to move to a higher orbital

• as electron falls back to its original orbital, it gives off energy

Light Reaction (Photo)

converts light energy to chemical energy (ATP) and electron carrier NADPH

• first stage of photosynthesis

  • occurs during the day

• occurs in thylakoid membrane

• sunlight is main player

What goes in/out of Light Reaction

Reactants: light energy, H2O, ADP, NADP+

Products: ATP, NADPH, O2

Where Light Reaction Products Go

• ATP: goes to Calvin cycle

• NADPH: goes to Calvin cycle

• O2: released from plant into environment

Chlorophyll Photosystems

• chlorophyll molecules in plant cells are surrounded by other chlorophyll molecules

• each molecule absorbs light energy from the sun

  • electrons jump up/fall back, give off energy

  • energy given off is transmitted to another chlorophyll molecule

    • causes an electron in that molecule to jump up/fall back

• located in thylakoid membrane

• linear electron flow

Photosystem I

• chlorophyll a (P700)

• reduced NADP+ to NADPH

Photosystem II

• chlorophyll a (P680)

• upstream of photosystem I

• charges photosystem I via electron transport chain

Calvin Cycle (Synthesis)

uses ATP and NADPH from light reaction to reduce CO2 to G3P

• anabolic

• after light reaction

• occurs in stroma

• not light dependent

• CO2 is main player

What Goes In/Out of Calvin Cycle

Reactants: 9 ATP & 6 NADPH from light reactions, 3 CO2 absorbed from atmosphere

Products: 9 ADP, 6 NADP+, 6 G3P (a 3 carbon sugar)

Where the G3P goes after Calvin Cycle

• one goes towards building sugar, starch, cellulose

• other 5 recycle back to RuBP in the regeneration stage

Sub-Phases of Calvin Cycle

1. carbon Fixation phase: catalyzed by rubisco

2. Reduction phase

3. Regeneration of RuBP (CO2 acceptor phase)