8.3 The Reactions of 8.3 The Reactions of PhotosynthesisPhotosynthesis

PigmentsPigments

• PigmentsPigments: molecules that reflect/absorb light energy: molecules that reflect/absorb light energy ChlorophyllChlorophyll a and b a and b

Contained in chloroplastsContained in chloroplasts Contains photo-sensitive membrane that can capture Contains photo-sensitive membrane that can capture

solar energysolar energy Reflects green light & absorbs all other colorsReflects green light & absorbs all other colors Capture slightly different wavelengths of energyCapture slightly different wavelengths of energy

Accessory pigmentsAccessory pigments Other colors also capture sunlight; pass energy to Other colors also capture sunlight; pass energy to

chlorophyllchlorophyll Xanthophylls, carotenoidsXanthophylls, carotenoids

ChloroplastsChloroplastsIn a plant

Micrograph of a chloroplast

Chloroplasts StructureChloroplasts Structure

Light Energy

Chloroplast

CO2 + H2O Sugars + O2

Section 8-2

Photosynthesis: Reactants and ProductsPhotosynthesisPhotosynthesis

Light-Dependent ReactionsLight-Dependent Reactions

Take place only in lightTake place only in light Four stepsFour steps

Light absorptionLight absorption Electron transportElectron transport Breaking of water/oxygen productionBreaking of water/oxygen production ATP formationATP formation

Light-Independent ReactionsLight-Independent Reactions

Do not require lightDo not require light Calvin CycleCalvin Cycle

Uses carbon dioxideUses carbon dioxide Forms glucose moleculeForms glucose molecule

The Photosynthesis EquationThe Photosynthesis Equation

lightlight

6CO6CO22 + 6H + 6H22OO C C66HH1212OO66 + 6O + 6O22 Carbon WaterCarbon Water Glucose Oxygen Glucose Oxygen

Dioxide (Sugar)Dioxide (Sugar)

Photosynthesis uses the energy from sunlight to convert water Photosynthesis uses the energy from sunlight to convert water and carbon dioxide into high-energy sugars and oxygenand carbon dioxide into high-energy sugars and oxygen

Energy Shuttling

Recall ATP: One phosphate group removed to liberate lots of energy = superb molecule for shuttling energy around within cells.

NADP+, NADPH also shuttles energy

Light-dependent Reactions (Thylakoid)

Photosystem: light capturing unit containing chlorophyll Electron transport system: electron carrier molecules

that shuttle electrons, energy released to make ATP Electrons in chlorophyll must be replaced by electrons

from water so that cycle may continue; oxygen is liberated from the light reactions

Light reactions make ATP and NADPH used to fuel the reactions of the Calvin cycle (light independent reactions)

Calvin Cycle (light independent or “dark” reactions) (STROMA)

ATP and NADPH from light reactions used to break CO2 apart, then reassemble the carbons into glucose.

Called carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (glucose)

Homework Assignment: due 2/11/13Homework Assignment: due 2/11/13

In your comp book:In your comp book:Label the parts of a chloroplast on diagram Label the parts of a chloroplast on diagram provided provided p. 231p. 231Organize information:Organize information:

Light-dependent reactions

Light-independent reactions

Definition

Where take place

Reactants

Products