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.