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.