Chapter 8 Photosynthesis
8.1 Overview of Photosynthesis
Importance of Photosynthesis
Photosynthesis is crucial for all living organisms as it provides energy and organic materials.
It removes carbon dioxide (CO2) from the atmosphere and releases oxygen (O2).
Autotrophs and Heterotrophs
Autotrophs: Organisms that produce their own food.
Photoautotrophs: Utilize sunlight for energy (e.g., plants, algae, cyanobacteria).
Chemoautotrophs: Extract energy from inorganic compounds (e.g., bacteria near deep-sea vents).
Heterotrophs: Organisms (e.g., animals, fungi) that obtain energy by consuming autotrophs.
Key Components of Photosynthesis
Primary substrates:
Water (H2O): Absorbed by roots from the soil.
Carbon dioxide (CO2): Acquired from air via stomata.
Sunlight: Provides energy for the process.
Products:
Glucose (sugar): Provides energy for living organisms.
Oxygen (O2): Byproduct released into the atmosphere.
8.2 The Light-Dependent Reactions of Photosynthesis
Light Energy and Its Absorption
Light energy consists of electromagnetic waves; different wavelengths carry varying energy levels.
Plants utilize the visible spectrum of light (400-700 nm).
Photosynthetic Pigments
Chlorophyll a & b: Key pigments that absorb light, primarily red and blue wavelengths, reflecting green.
Carotenoids: Accessory pigments (e.g., β-carotene) that protect the plant from excess light and absorb other wavelengths.
Structure of Thylakoid Membranes
Thylakoids contain:
Photosystems I and II: Sites for light absorption and energy conversion.
Electron Transport Chain (ETC): Transmits electrons and assists in ATP synthesis.
Enzyme Complexes: Include ATP synthase and NADP reductase for energy conversion.
Key Processes in Light Reactions
Light Absorption: Light excites electrons in chlorophyll, and these electrons are transferred through the ETC.
Water Splitting: In photosystem II, water is split to replace lost electrons, producing oxygen.
ATP and NADPH Production: Energy from moving electrons establishes a proton gradient used by ATP synthase to produce ATP.
8.3 Using Light Energy to Make Organic Molecules
The Calvin Cycle
Three key stages:
Carbon Fixation: CO2 is added to ribulose bisphosphate (RuBP) by Rubisco, resulting in 3-phosphoglycerate (3-PGA).
Reduction: ATP and NADPH convert 3-PGA to glyceraldehyde-3-phosphate (G3P), a form of sugar.
Regeneration: G3P is utilized to regenerate RuBP, allowing the cycle to continue.
Summary of the Calvin Cycle
Inputs: 3 CO2, ATP, NADPH.
Outputs: G3P (converted to glucose), with three cycles producing one G3P.
Energy Cycle Implications
Photosynthesis supports the energy cycle in living organisms, as the energy stored in glucose is transferred through food webs.
Chapter 8 Photosynthesis
8.1 Overview of Photosynthesis
Importance of Photosynthesis
Photosynthesis is crucial for all living organisms as it provides energy and organic materials.
It removes carbon dioxide (CO2) from the atmosphere and releases oxygen (O2).
Autotrophs and Heterotrophs
Autotrophs: Organisms that produce their own food.
Photoautotrophs: Utilize sunlight for energy (e.g., plants, algae, cyanobacteria).
Chemoautotrophs: Extract energy from inorganic compounds (e.g., bacteria near deep-sea vents).
Heterotrophs: Organisms (e.g., animals, fungi) that obtain energy by consuming autotrophs.
Key Components of Photosynthesis
Primary substrates:
Water (H2O): Absorbed by roots from the soil.
Carbon dioxide (CO2): Acquired from air via stomata.
Sunlight: Provides energy for the process.
Products:
Glucose (sugar): Provides energy for living organisms.
Oxygen (O2): Byproduct released into the atmosphere.
8.2 The Light-Dependent Reactions of Photosynthesis
Light Energy and Its Absorption
Light energy consists of electromagnetic waves; different wavelengths carry varying energy levels.
Plants utilize the visible spectrum of light (400-700 nm).
Photosynthetic Pigments
Chlorophyll a & b: Key pigments that absorb light, primarily red and blue wavelengths, reflecting green.
Carotenoids: Accessory pigments (e.g., β-carotene) that protect the plant from excess light and absorb other wavelengths.
Structure of Thylakoid Membranes
Thylakoids contain:
Photosystems I and II: Sites for light absorption and energy conversion.
Electron Transport Chain (ETC): Transmits electrons and assists in ATP synthesis.
Enzyme Complexes: Include ATP synthase and NADP reductase for energy conversion.
Key Processes in Light Reactions
Light Absorption: Light excites electrons in chlorophyll, and these electrons are transferred through the ETC.
Water Splitting: In photosystem II, water is split to replace lost electrons, producing oxygen.
ATP and NADPH Production: Energy from moving electrons establishes a proton gradient used by ATP synthase to produce ATP.
8.3 Using Light Energy to Make Organic Molecules
The Calvin Cycle
Three key stages:
Carbon Fixation: CO2 is added to ribulose bisphosphate (RuBP) by Rubisco, resulting in 3-phosphoglycerate (3-PGA).
Reduction: ATP and NADPH convert 3-PGA to glyceraldehyde-3-phosphate (G3P), a form of sugar.
Regeneration: G3P is utilized to regenerate RuBP, allowing the cycle to continue.
Summary of the Calvin Cycle
Inputs: 3 CO2, ATP, NADPH.
Outputs: G3P (converted to glucose), with three cycles producing one G3P.
Energy Cycle Implications
Photosynthesis supports the energy cycle in living organisms, as the energy stored in glucose is transferred through food webs.
