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4 Photosynthesis

Photosynthesis Overview

Photosynthesis is a process where plants, algae, and certain bacteria use sunlight to produce energy-rich organic molecules.

Energy Capture

  • Energy used by living cells is derived from the sun and converted into a biologically usable form through photosynthesis.

  • Photosynthesis occurs mainly in green parts of plants, primarily in the leaves.

Requirements for Photosynthesis

  • Inputs: Light energy, Carbon Dioxide (CO2), and Water (H2O).

  • Outputs: Organic sugar (glucose) and Oxygen (O2).

Key Components

  • Chlorophyll: The green pigment in chloroplasts, essential for capturing light energy.

  • Chloroplast: A plant organelle that traps light energy and houses the photosynthesis processes.

Definitions of Key Terms

  • H2O: Water

  • O2: Oxygen

  • CO2: Carbon Dioxide

  • ADP: Adenine Diphosphate (low energy form)

  • ATP: Adenosine Triphosphate (high energy form)

  • NADP+/NADPH: Nicotinamide Adenine Dinucleotide Phosphate (involved in electron transfer).

  • PGA: Phosphoglyceric Acid (3-carbon compound).

  • RuBP: Ribulose Bisphosphate (5-carbon sugar-phosphate).

ATP Functionality

  • ATP plays a crucial role in transferring chemical energy within the cell to energy-requiring reactions.

Photosynthesis Equation

  • The simplified equation for photosynthesis is:

    • 6CO2 + 12H2O + Light Energy -> C6H12O6 + 6O2 + 6H2O.

  • CO2 combines with H2O under sunlight to form glucose while oxygen is released.

Stages of Photosynthesis

  • Light Reactions: Capture of sunlight, creation of ATP, NADPH, and splitting of water, releasing O2.

  • Calvin Cycle (Dark Reactions): Utilizing ATP and NADPH to convert CO2 into organic molecules.

Reduction/Oxidization (REDOX)

  • Reducing Agent: A substance that donates electrons, thus is oxidized in the process.

  • Oxidizing Agent: A substance that accepts electrons, thus is reduced.

  • OIL RIG Mnemonic: Oxidation Is Loss, Reduction Is Gain (of electrons).

Light Reactions

  • Create high-energy electrons from photons that facilitate ATP and NADPH formation.

  • Involve two photosystems that absorb light.

The Calvin Cycle

  • Does not require light directly.

  • Uses ATP and NADPH to synthesize organic molecules from CO2.

  • The cycle regenerates RuBP to continue the process.

Photorespiration

  • Occurs when Rubisco, the enzyme involved in carbon fixation, also reacts with O2, hindering sugar production.

C4 Plants

  • Utilize an alternative method of CO2 fixation to minimize photorespiration losses. More efficient in hot climates.

Pigments in Photosynthesis

  • Chlorophyll a & b: Main pigments absorb light for photosynthesis.

  • Accessory Pigments (Carotenoids): Capture light energy at different wavelengths.

Factors Affecting Photosynthesis

  • Light levels and quality, water availability, CO2 concentration, and temperature.

Cellular Respiration Overview

  • Breakdown of sugar molecules to release energy via glycolysis, Krebs cycle, and oxidative phosphorylation.

  • Aerobic (requires O2) vs. Anaerobic (does not require O2) respiration.

Glycolysis

  • Occurs in the cytoplasm, converting glucose to pyruvic acid, producing energy (ATP).

  • Some pyruvate is driven to the Krebs cycle while others may undergo fermentation in anaerobic conditions.

Krebs Cycle

  • Performs in mitochondria, breaks down Acetyl-CoA to produce NADH, FADH2, ATP, CO2, and H2O.

  • Involves multiple enzyme-catalyzed reactions, regenerating starting molecules to sustain the cycle.

Electron Transport Chain

  • Final aerobic respiration stage, where high-energy electrons pass through carriers to produce ATP.

  • Oxygen is vital as the final electron acceptor; lack of oxygen leads to anaerobic pathways like fermentation.