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Chapter 8 Photosynthesis (1)

Chapter 8: Photosynthesis

Overview of Photosynthesis

  • Photosynthesis is crucial for producing energy and carbon sources for plants and other living organisms.

  • It removes CO2 from the atmosphere and releases O2 as a by-product.

  • Both photosynthesis and cellular respiration occur in plants, algae, and photosynthetic bacteria.

Learning Objectives

  • Explain the significance of photosynthesis to other living organisms.

  • Describe the main structures involved in photosynthesis.

  • Identify the substrates and products of photosynthesis.

Autotrophs and Heterotrophs

  • Types of Autotrophs:

    • Photoautotrophs: Use sunlight to create food from inorganic molecules (e.g., plants, algae, cyanobacteria).

    • Chemoautotrophs: Capture energy from inorganic compounds to produce organic compounds (e.g., thermophilic bacteria in deep sea vents).

  • Heterotrophs: Organisms including animals, fungi, and bacteria that rely on sugars produced by autotrophs for energy.

Photosynthesis Process

  • Reaction Overview:

    • Uses solar energy, carbon dioxide (CO2), and water (H2O) to produce organic molecules (sugars) with oxygen produced as a waste.

Components Needed for Photosynthesis

  • Water (H2O): Absorbed by roots from the soil.

  • Carbon dioxide (CO2): Acquired from air through stomata for gas exchange.

  • Oxygen (O2): Waste product released via stomata.

  • Sunlight: Provides the energy necessary for the process.

Leaf Structure and Chloroplasts

  • Chloroplasts: Double-membraned organelles containing stroma, thylakoids (arranged in granas), and thylakoid lumen.

  • High-density chloroplasts are found in mesophyll cells of leaves.

Photosynthesis Equation

  • Involves complex metabolic pathways: Light Reaction and Calvin Cycle.

Light-Dependent Reactions

  • Convert light energy into chemical energy, producing ATP and NADPH.

  • Occur in thylakoid membranes of chloroplasts.

  • Calvin Cycle uses ATP and NADPH to produce sugars in the stroma of chloroplasts.

Structure of Thylakoid Membranes

  • Components include:

    • Photosystems I and II (sites of light absorption).

    • Electron Transport Chain (ETC).

    • Enzymatic complexes like NADP reductase and ATP synthase.

Photosystems

  • Consist of light-harvesting complexes and reaction centers.

  • In Photosystem II, electrons come from the splitting of water, releasing O2.

  • In Photosystem I, electrons come from the ETC.

Electron Transport Chains (ETC)

  • Transports electrons and protons (H+) to create a gradient (used to produce ATP).

  • Final electron acceptor is NADP+ which forms NADPH.

The Calvin Cycle (Light-Independent Reactions)

  • Three stages:

    1. Fixation: CO2 added to RuBP by Rubisco, producing 3-PGA.

    2. Reduction: ATP and NADPH convert 3-PGA into G3P (sugar).

    3. Regeneration: G3P is used to regenerate RuBP.

  • Overall, three cycles are necessary to produce one G3P.

Overall Process of Photosynthesis

  • Inputs: H2O, CO2, Light.

  • Outputs: O2, Glucose, NADPH, ATP.

  • The process is vital for the energy cycle of all living organisms.