section 9.2 photosynthesis: an overview · chlorophyll •light energy from the sun must be...
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Section 9.2 Photosynthesis: An Overview
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I Can…
• LS 1.8 I can create a model that supports the relationship of chloroplast structure to its function.
• LS 1.8 I can develop a model to explain the flow of matter and energy in photosynthesis.
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Key Questions
1. What role do pigments play in the process of photosynthesis?
2. What are the electron carrier molecules?
3. What are the reactants and products of photosynthesis?
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Vocabulary
• Pigment
• Chlorophyll
• Thylakoid
• Stroma
• NADP+
• Light-dependent reactions
• Light-independent reactions
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Chlorophyll
• Light energy from the sun must be captured
• Sunlight is perceived as “white” light, but is a mixture of different wavelengths • Known as the visible spectrum
• Plants gather the sun’s energy with light-absorbing molecules called pigments.
• The principle pigment of green plants is known as chlorophyll. • Chlorophyll a and b- do not absorb green light
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Plants also contain red and orange pigments, such as carotene.
Chlorophyll breaks down first as temperature drops in autumn, leaving the reds and oranges to see.
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Chloroplasts
• Photosynthesis takes place inside organelles called chloroplasts. • Surrounded by two membranes
• Filled with chlorophyll-containing membranes called thylakoids • Interconnected and in stacks called
grana (singular: granum)
• The fluid-portion of the chloroplast, outside the thylakoids, is known as the stroma.
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Energy Collection
• Chlorophyll and other pigments absorb light and transfer the energy to their own electrons.
• These high-energy electrons are then available to do chemical work, like building sugar molecules.
• The high-energy electrons produced by chlorophyll are highly reactive and require a special “carrier.”
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High-Energy Electrons
• An electron carrier is a compound that can accept a pair of high-energy electrons and transfer them, along with most of their energy, to another molecule.
• NADP+ accepts and holds 2 high-energy electrons along with a hydrogen ion (H+). This converts the NADP+ into NADPH.
• NADPH can carry the high-energy electrons that were produced by light absorption in chlorophyll to chemical reactions elsewhere in the cell.
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An Overview of Photosynthesis
• Photosynthesis uses the energy of sunlight to covert water and carbon dioxide (low-energy reactants) into high-energy sugars and oxygen (products).
6CO2 + 6H2O C6H12O6 + 6O2
carbon dioxide + water sugars + oxygen
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The Two Reactions of Photosynthesis
1. The light-dependent reactions • Location: thylakoid membrane
2. The light-independent reactions • Also called the Calvin cycle of Dark reaction
• Location: stroma
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Section 9.2 Exit Ticket
1. What is the role of pigments in photosynthesis?
2. What are the differences between the light-dependent and light-independent reactions of photosynthesis?
3. How are molecules recycled between the light-dependent and light-independent reactions of photosynthesis?
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The End