5.2 energy for biological processes

• Photosynthesis is a reaction where light energy is used to split water molecules through photolysis to combine hydrogen with carbon dioxide to produce glucose
• Oxygen is a waste product of photosynthesis and is released into the atmosphere
• The rate of photosynthesis is determined by carbon dioxide concentration, light intensity, and temperature
• Chloroplast is the site of photosynthesis and is adapted with stacks of thylakoid membranes called grana containing chlorophyll and stroma containing enzymes for the light-independent stage
• Two stages of photosynthesis:

  • Light-dependent reaction: electrons are excited by chlorophyll in thylakoid membranes, generating ATP and reduced NADP
  • Light-independent reaction (Calvin cycle): uses ATP and reduced NADP to produce glucose
• Limiting factors of photosynthesis include light intensity, CO2 concentration, and temperature
• Respiration:

  • Aerobic respiration releases carbon dioxide and reunites hydrogen with oxygen to produce energy
  • Anaerobic respiration occurs without oxygen
  • Glycolysis is the first step, producing pyruvate, NADH, and ATP
  • Krebs cycle oxidizes glucose to produce CO2, ATP, reduced NAD, and reduced FAD
  • Oxidative phosphorylation in the electron transport chain synthesizes ATP
• In oxidative phosphorylation:

  • Reduced coenzymes carry hydrogen ions and electrons to the electron transport chain
  • Electrons are passed through redox reactions, moving hydrogen ions across the inner mitochondrial membrane
  • ATP is produced using ATP synthase
  • Hydrogen atoms combine with oxygen to produce water
• Theoretical yield of 38 ATP molecules per glucose molecule in respiration, but in reality, this is rarely achieved due to membrane leakiness

  • Respiratory substrates include carbohydrates, lipids, and proteins
  • Respiratory quotient (RQ) can determine the respiratory substrate being used
  • Different substrates have different RQ values: carbohydrates (1.0), lipids (0.8), proteins (0.9)
• Anaerobic respiration occurs when oxygen is low, allowing glycolysis to continue

  • In mammals, pyruvate is converted to lactate to reoxidize NADH
  • Yeast and plants use alcoholic fermentation to continue glycolysis