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

Carbon Water

O C

6

H

12

O

6

+ 6O

2

Glucose Oxygen

Dioxide (Sugar)

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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