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
• Factors affecting photosynthesis:

  • Light intensity
  • CO2 concentration
  • 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
• Link reaction: converts pyruvate to acetyl, reducing NAD to NADH and producing CO2

  • Krebs cycle: oxidises glucose to produce CO2, ATP, reduced NAD, and reduced FAD
• Oxidative phosphorylation:

  • ATP synthesis in the electron transport chain in mitochondria
  • Hydrogen ions and electrons carried by coenzymes to generate ATP
  • Oxygen acts as the final electron acceptor
• Respiratory substrates include carbohydrates, lipids, and proteins

  • Respiratory quotient (RQ) can determine the respiratory substrate being used
  • Different RQ values for carbohydrates, lipids, and proteins
• Anaerobic respiration:

  • ATP production continues through glycolysis
  • In mammals, pyruvate is converted to lactate
  • Yeast and plants use alcoholic fermentation to enable glycolysis to continue