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.