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7_8. Photosynthesis Presentation

Photosynthesis Experiment

  • Setup Experiment:

    • Two mice are placed in separate containers, one with a plant.

    • Observation of the mouse without the plant dying due to lack of oxygen, illustrating the consequences of photosynthesis.

  • Conclusion:

    • Emphasizes the importance of photosynthesis for oxygen production, humorously refers to its known existence before the experiment.

Course Objectives

  • Compare & Contrast Cellular Processes:

    • Focus on cellular respiration, fermentation, and photosynthesis regarding:

      • Overall reaction

      • Stages

      • Energy yield

      • Cellular location in prokaryotic and eukaryotic cells.

  • Photosynthesis Components:

    • Pigments to harvest light energy.

    • Light-Dependent Reactions: Photosystems, Electron Transport Chain, Reduction of NADP+, ATP synthesis.

    • Calvin Cycle: Involves CO2 fixation, carbohydrate production, regeneration of RuBP.

    • Plant Adaptations: C3 plants, C4 plants & CAM plants.

Pre-Existing Knowledge Assessment

  • Levels of understanding about photosynthesis:

    • Options ranging from no knowledge to clear comprehension that one can explain to others.

  • Key Vocabulary:

    • Autotroph, Proton, Pigment, Electron Transport Chain, Photon, Oxidative Phosphorylation.

Tree Mass Sources

  • Sources of Dry Mass in Trees:

    • Soil nutrients

    • Air taken through leaves

    • Water absorbed by roots

    • Sunlight hitting leaves.

Energy Requirements of Organisms

  • Energy Sources:

    • Heterotrophs: Obtain energy by consuming organic molecules.

    • Autotrophs: Synthesize organic molecules from inorganic sources (e.g., CO2, H2).

    • Photoautotrophs: Use light as an energy source for producing organic molecules.

Carbon Cycle Involvement

  • Photosynthesis contributes to:

    • Formation of organic molecules from sunlight utilizing photoautotrophs.

  • Cellular respiration employs these organic molecules to generate ATP and energy for organisms.

Summary of Photosynthesis Reaction

  • Equation:

    • 6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2

    • Components include Carbon, Water, Light, and the products Sugar and Oxygen.

Photosynthesis Location

  • Occurs in Chloroplasts:

    • Primarily in leaf cells rich in chloroplasts.

    • Water sourced from root absorption; gas exchange (CO2 & O2) through stomata.

Chloroplast Structure

  • Chloroplast Anatomy:

    • Thylakoid Membrane: Forms thylakoids containing pigments (e.g., chlorophyll).

    • Stroma: Fluid space between membranes, where the Calvin Cycle occurs.

Photosynthesis Process Overview

  • Light-Dependent Reactions: Produce ATP and NADPH using light energy.

  • Calvin Cycle: Utilizes energy from ATP and NADPH to synthesize sugar.

Role of NADP+ and NADPH

  • Electron Transfer:

    • NADP+ acts as an electron acceptor, getting reduced to NADPH during light reactions, carrying electrons for synthesizing carbohydrates.

Light-Dependent Reactions

  • Location: Thylakoid membranes.

  • Converts light energy into chemical energy in ATP and NADPH, producing oxygen.

  • Critical for sustaining aerobic respiration, supplying most of Earth's oxygen.

Understanding Light Energy

  • Electromagnetic Radiation:

    • Light is made of photons traveling in wave patterns, with visible light detectable by human eyes (380-740nm).

    • The sun emits a full spectrum, but the atmosphere blocks some.

Pigment Functionality

  • Color Perception:

    • Objects reflect wavelengths of light, interpreted by the brain as colors.

    • Plants primarily appear green due to chlorophyll, which absorbs other wavelengths.

Leaf Color Changes in Autumn

  • Chlorophyll Degradation:

    • As the growing season ends, chlorophyll breaks down, revealing other pigments like carotenoids.

Pigment Mechanism

  • Excitation of Electrons:

    • Absorption of light energy boosts electrons to higher energy states.

    • This can lead to heat release or fluorescence.

Electron Transport Chain (ETC) Functionality

  • ETC Role:

    • Transports excited electrons, creating a proton gradient across the thylakoid membrane to drive ATP synthesis through chemiosmosis.

Replacing Excited Electrons

  • Water Splitting:

    • Water molecules provide protons and electrons for replacing those used in photosystems, contributing to O2 production.

Photosystem Functions

  • Photosystem I details:

    • Light-harvesting complex that re-excites electrons for participation in the second ETC.

    • Results in NADPH formation without proton pumping.

Generating H+ Gradient

  • Mechanisms:

    • ETC and water splitting enhance H+ concentration in the thylakoid lumen.

Summary of Light Reaction Steps

  • Main processes include oxygen production, ATP formation via chemiosmosis, and NADP+ reduction to NADPH.

Photosynthesis and Oxygen Catastrophe

  • Historical Perspective:

    • Cyanobacteria initiation of O2 production drastically altered the atmosphere, causing significant extinction events.

  • Transition from primitive anaerobic life to oxygen-breathing organisms.

Calvin Cycle Overview

  • Light-independent reactions that synthesize carbohydrates using ATP, NADPH, and CO2 in the stroma.

Importance of Carbohydrates

  • Energy Source:

    • Serve as precursors for organic molecules and energy storage for both plants and animals.

Calvin Cycle Stages

  • Three Main Stages:

    1. Carbon Fixation: Incorporating CO2.

    2. Reduction Phase: Conversion processes utilizing ATP and NADPH.

    3. Regeneration: Preparing the cycle for the next round of carbon fixation.

Review of Light-Dependent Reactions

  • Recap of electron transport, ATP generation, and oxygen production.

Review of Calvin Cycle

  • Final output includes Glyceraldehyde-3- phosphate (G3P) and the conversion to glucose.

Understanding Photorespiration in C3 Plants

  • Challenges in low CO2 and high O2 conditions, resulting in less efficient forms of carbon fixation by rubisco.

Stomatal Functionality

  • Gas Exchange Regulation:

    • Stomata open during day but close in hot, dry conditions to conserve water, affecting CO2 intake.

C4 Plant Adaptations

  • Efficient CO2 Utilization:

    • Structure allows for better function under low CO2 conditions with spatial separation between gas uptake and photosynthesis.

C3 vs. C4 Plants

  • Adaptation to Environment:

    • C4 plants thrive in hot, arid climates while C3 plants flourish in cooler surroundings, highlighting their metabolic adaptations.

CAM Plants Characteristics

  • Water Conservation:

    • Adaptation for arid conditions allows CO2 fixation at night to minimize water loss.

Compare & Contrast Cellular Respiration and Photosynthesis

  • Differences in end products, locations, and energy sources.

  • Similarities in metabolic processes, glucose involvement, and ATP synthesis utilization.