Plant Biology: Oxygenic Photosynthesis

Oxygenic Photosynthesis

• Oxygenic photosynthesis converts light energy into chemical energy and reducing power.
• Chemiosmosis is used to create ATP.
• NADP+ reductase converts NADP+ to NADPH.

Photosynthesis Summary

• Photosynthesis converts light energy into chemical energy and reducing power.
• Chemiosmosis generates ATP.
• NADP+ reductase forms NADPH.

Recommended Textbook

• Smith, & Smith, A. M. (Alison M. 2010). Plant biology. Garland Science. ISBN: 9780815340256
• 3 copies available in the Main Library, General Shelving; 580 P 713.

Photosynthesis Learning Objectives

• Understand photosynthetic use of different wavelengths of light.
• Know the structure of chloroplasts.
• Understand the structure, function and molecular mechanism of photosystems I and II.
• Förster resonant energy transfer.
• Convert light into chemical energy.
• Generate H+ gradients.
• Understand electron transport.
• Recognize how herbicides target photosynthesis.
• Understand how chloroplasts adjust to environmental changes.

What has Photosynthesis Ever Done for Us?

• Graph showing oxygen levels in the atmosphere throughout time.
• Photosynthesis's role in creating the Earth's oxygen-rich atmosphere and supporting life.

Cyanobacteria and Chloroplasts

• Cyanobacteria are photosynthetic organisms.
• Chloroplasts have similar structural features to cyanobacteria, suggesting a common ancestry.
• Images comparing cyanobacteria and chloroplast structure.

Chloroplast Structure

• The chloroplast contains stroma, thylakoid (inner and outer bilayer membranes), grana, and lumen.

Thylakoid Structure

• The thylakoid membrane contains photosystems II and I, cytochrome b6f complex, and ATP synthase.

The Structure of a Thylakoid

• The diagram shows the movement of electrons and protons through photosystems, to generate ATP and NADPH used in the Calvin cycle.

Why are Chloroplasts Green?

• Chlorophyll absorbs light most strongly in the blue and red regions of the spectrum, reflecting green light.

Photosynthetically Active Radiation (PAR)

• Graph demonstrating different wavelengths of light absorbed by different types of chlorophyll.

Photosynthesis Summary (Alternative)

• Conversion of light energy into chemical energy and reducing power.
• Chemiosmosis produces ATP.
• NADP+ reductase forms NADPH.

Photosynthesis Summary (Diagram)

• The diagram illustrates the steps in photosynthesis, including light excitation, energy transfer, charge separation, electron transfer, and ATP synthesis.

Chlorophyll

• Chlorophyll a and b are key pigment molecules in photosynthesis, with slightly different absorption spectra.
• Chemistry diagrams show the chemical structure of chlorophyll.

Structure of a Photosystem

• Diagram showing the light harvesting complex surrounding the core complex of chlorophyll a molecules that drive the electron transfer.

Light Harvesting Complex

• Accessory pigments enhance light harvesting efficiency.
• Diagram shows how accessory pigments capture light and transfer the energy to a central chlorophyll.

Chlorophyll Energy Transfer

• Förster resonance energy transfer, transferring energy from one chlorophyll molecule to another.

Photosystems, ETC, and ATP Synthesis

• Diagram illustrating the electron transport chain (ETC) and ATP synthesis in the thylakoid membrane.

The Z-Scheme

• Diagram outlines the Z-scheme, the overall process of light-driven electron transport.

Photosystems, ETC, and ATP Synthesis (Alternative)

• Diagram illustrating the ETC, showing electron flow and proton gradient across the thylakoid membrane, driving ATP synthesis.

Photosystem II-Oxygen Producing

• Diagram shows the components of photosystem II and the step-by-step process that split water molecules to release electrons and oxygen.

Photosystem I - NADPH Producing

• Diagram illustrates the components of photosystem I and the transfer of electrons for NADPH production.

Photosynthesis and the Environment

• Factors like day/night cycles, cloud cover, canopy cover, and high exposure influence photosynthesis rates.

Too much Light - PSII

• Explanation of rate limiting steps in photosynthesis.

Too much Light - Non-photochemical Quenching

• Explanation of the mechanism of non-photochemical quenching, and how the plant protects itself from excessive light.

Too much Light- PSI

• Explanation of rate limiting steps in photosynthesis when photosystem I is impacted by too much light.

Too Much Light - The Water-Water Cycle

• Diagram illustrating the mechanism of cyclic electron transport, and roles of different enzymes in response to excessive light.

Herbicides

• Effects of herbicides on photosynthetic processes.

###Herbicide Deactivation

• Diagram showing how herbicides disrupt electron transport in photosynthesis.

Cyclic Photosynthesis

• Cyclic photosynthesis pathway in plants.
• Diagram illustrates the cyclic electron pathway without water being split.

Cyclic Photosynthesis (Alternative)

• Mechanism of cyclic photosynthesis used by purple and green bacteria, and under certain conditions in plants.

Comparison with Aerobic Respiration

• Photosynthesis vs. aerobic respiration, highlighting the contrasting input/output requirements.

Summary

• Photosynthesis converts light to chemical energy.
• ATP is formed via chemiosmosis during electron transfer.
• Two linked photosystems are crucial for efficient electron transfer from water to NADPH.

Further Reading

• Additional topics to explore regarding photosynthesis, including why there's only one electron path in PSII, cyclic photosynthesis, effects of blue light absorption, and differences in plant compensation points between species.

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