Photosynthesis Overview

Photosynthesis

• Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy in the form of glucose.
• It occurs in chloroplasts, organelles found in plant cells and some algae.
• The primary inputs for photosynthesis are light energy, water (H₂O), and carbon dioxide (CO₂).
• Oxygen (O₂) is a byproduct.
• The overall chemical reaction for photosynthesis is: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
• Photosynthesis involves two main stages: light-dependent reactions and the light-independent reactions (Calvin cycle).
• Light-dependent reactions take place in the thylakoid membranes, using light energy to create ATP and NADPH. Water is split, releasing O₂.
• Light-independent reactions (Calvin cycle) occur in the stroma. ATP and NADPH from the light-dependent reactions are used to convert CO₂ into glucose.
• Factors affecting photosynthesis include light intensity, CO₂ concentration, temperature, and water availability.
• Increased light intensity boosts photosynthetic rates up to a maximum; further increases have no effect.
• Higher CO₂ levels increase photosynthetic rates up to a saturation point.
• Temperature affects the process; optimal rates occur within a specific range, and lower or higher temperatures can inhibit it.
• Water is crucial, acting as a reactant.

Cellular Respiration

• Cellular respiration is the process cells use to break down glucose and release energy as ATP.
• This process occurs in both plant and animal cells.
• The primary inputs for cellular respiration are glucose (C₆H₁₂O₆) and oxygen (O₂).
• The overall chemical reaction is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP).
• Cellular respiration occurs in three stages: glycolysis, the Krebs cycle, and the electron transport chain.
• Glycolysis happens in the cytoplasm, breaking down glucose into pyruvate, generating a small amount of ATP.
• The Krebs cycle, in the mitochondrial matrix, further oxidizes pyruvate, producing more ATP, NADH, and FADH₂.
• The electron transport chain, in the inner mitochondrial membrane, uses NADH and FADH₂ to produce a large amount of ATP via chemiosmosis.
• Maximum ATP production per glucose molecule is approximately 36 or 38, but this can vary between cells.
• Anaerobic respiration (fermentation) occurs without oxygen, yielding less ATP than aerobic respiration. Byproducts include lactic acid or ethanol.
• Oxygen is essential for aerobic respiration. Without oxygen, cells rely on anaerobic respiration, producing fewer ATP molecules.
• Factors impacting cellular respiration are oxygen availability, temperature, and glucose concentration.

Relationship Between Photosynthesis and Cellular Respiration

• Photosynthesis and cellular respiration are reverse processes.
• Photosynthesis stores energy in glucose, while cellular respiration releases energy from glucose.
• Photosynthesis produces oxygen, and cellular respiration consumes it.
• Photosynthesis absorbs carbon dioxide, and cellular respiration releases it.