PHOTOSYNTHESIS

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PHOTOSYNTHESIS
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Photosynthesis
Light Making

• The source of all life energy?
• Performed by Green Plants
• E 6CO2 6H2O C6 H12O6 6O2

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I. Structure of chloroplasts

• A. Diagram

Grana
Reservoir
Inner and Outer membranes
Thylakoid membranes
Stroma
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TEM View
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B. Thylakoid membranes have

• Embedded chlorophyll and other pigments
• Molecules of the electron transport chain
• Protein complexes to make ATP

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C. Stroma

• Has enzymes that join carbons together to form
  carbohydrates

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II. Trapping light energy

• A. Photosynthetic pigments
• Absorb light
• Why are plants green?
• Because they absorb red and blue

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Visible light
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Pigment absorbtion
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B. Chlorophylls - main pigments

• Several types
• e.g. chlorophylls a, b, c, d
• Excite electrons

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C. Accessory Pigments

• a. Capture light of various wavelengths other
  than those collected by chlorophylls
• b. Example carotenoids
• Yellow and red leaves in the fall
• Carrots?

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1. Carotenoids

• Also detoxify peroxy radicals that could destroy
  chlorophyll

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D. Photosystems

• Groups of pigments that capture light
• Two types
• 1. Photosystem 1
• Absorbs light of an average of 700 nM and so is
  called P700
• 2. Photosystem 2
• Absorbs and average of 680nM (P680)

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III. What happens in photosynthesis, an overview

• A. Light absorption
• B. Electron transport chain
• C. Chemiosmosis
• D. Carbon fixation

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IV Light Absorption and electron flow

• A. Happens in the thylakoids
• B. Cyclic and noncyclic electron flow

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C. Chemiosmotic ATP synthesis
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V. Carbon fixation

• Diagram

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VI. Rate of photosynthesis

• Controlled by
• A. Amount of light
• B. Heat
• C. Transport of H2O, CO2, O2
• Photorespiration?

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VII. Ecological aspects of photosynthesis

• Plants in different ecosystems have different
  needs
• A. C4 method of carbon fixation
• Hatch Slack pathway
• Used by bermuda grass, bamboo, and other tropical
  plants

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C3 and C4 leaves
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C4 path continued

• 1. Used by tropical plants.
• Conditions?
• Much light , warm, humid
• 2. Light is absorbed by one cell and carbon
  fixation happens in another
• 3. Avoids photorespiration
• 4. Fast but somewhat inefficient. Plants grow
  rapidly

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B. Crassulacean acid metabolism (CAM)

• 1. Used by desert succulents
• 2. Conditions
• Hot, dry, very intense light
• 3. These plants close stomata during the day to
  conserve water
• 4. At night, stomata open and CO2 is stored in
  organic acids
• 5. During the day CO2 is removed from acid and
  used in C3 cycle

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C. Sun plants and shade plants

• 1. Sun plants are designed for full sun
• Have thick, lobed leaves
• More pallisade mesophyll
• More stomata
• More RuBP carboxylase
• 2. Shade plants designed for low light
• Thinner leaves
• Fewer photosynthetic cells, more chlorophyll
• Slow photosynthesis in all light conditions

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• 3. Some trees have both sun leaves and shade
  leaves on the same plant
• e.g. oak trees