Notes on Photosynthesis

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8.3 The Reactions of Photosynthesis

Pigments

Pigments

: molecules that reflect/absorb light energy 

Chlorophyll

a and b  Contained in chloroplasts   Contains photo-sensitive membrane that can capture solar energy  Reflects green light & absorbs all other colors  Capture slightly different wavelengths of energy Accessory pigments  Other colors also capture sunlight; pass energy to chlorophyll  Xanthophylls, carotenoids

Chloroplasts

In a plant Micrograph of a chloroplast

Chloroplasts Structure

Section 8-2 Photosynthesis: Reactants and Products

Photosynthesis

Light Energy CO 2 + H 2 O Chloroplast Sugars + O 2

Light-Dependent Reactions

 Take place only in light  Four steps  Light absorption  Electron transport  Breaking of water/oxygen production  ATP formation

Light-Independent Reactions

 Do not require light  Calvin Cycle  Uses carbon dioxide  Forms glucose molecule

The Photosynthesis Equation

light 6CO 2 + 6H 2 O Carbon Water C 6 H 12 Dioxide (Sugar) O 6 + 6O 2 Glucose Oxygen Photosynthesis uses the energy from sunlight to convert water and 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 CO 2 apart, then reassemble the carbons into glucose.

 Called

carbon fixation

: taking carbon from an inorganic molecule (atmospheric CO 2 ) and making an organic molecule out of it (glucose)

Homework Assignment: due 2/11/13

In your comp book:  Label the parts of a chloroplast on diagram provided

p. 231

 Organize information:

Light-dependent reactions Light-independent reactions

Definition Where take place Reactants Products

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