Topic 5

• Photosynthesis is a two stage reaction with light dependent and light independent reactions
• Chloroplast


  • Thylakoid membrane and stacks (grana) - site of light dependent reactions
  • Stroma - site of light independent reactions
  • Inner and outer membranes
• Light dependent reactions


  1. Photolysis (splitting of water)

  2. Photoionization of chlorophyll

  3. Chemiosmosis (proton gradient and ATP synthesis)

  4. Production of ATP and reduced NADP
• Light independent reactions (Calvin cycle)

  1. Carbon dioxide fixation by rubisco

  2. Reduction of 3-carbon compounds using ATP and reduced NADP

  3. Regeneration of 5-carbon rubp
• Limiting factors


  Factors that reduce the rate of photosynthesis (light intensity, carbon dioxide concentration, temperature)
• Aerobic respiration


  1. Glycolysis (cytoplasm)

  2. Link reaction (mitochondrial matrix)

  3. Krebs cycle (mitochondrial matrix)

  4. Oxidative phosphorylation (mitochondrial membrane)
• Glycolysis


  Glucose is phosphorylated, converted to pyruvate, producing some ATP and reduced NAD
• Link reaction


  Pyruvate is oxidized to acetyl-CoA, producing CO2 and more reduced NAD
• Krebs cycle


  Acetyl-CoA enters, series of redox reactions, produces ATP, reduced NAD and FADH2, and CO2
• Oxidative phosphorylation


  Reduced coenzymes release H+, electrons transported along chain, proton gradient used to produce large amounts of ATP
• Oxidative phosphorylation produces 34 ATP per glucose molecule
• Oxidative phosphorylation


  The final step in cellular respiration, very similar to chemiosmosis in the light-dependent reaction of photosynthesis
• Oxidative phosphorylation is where most of the ATP is produced
• Oxidative phosphorylation


  1. Reduced coenzymes release hydrogen, splitting into protons and electrons

  2. Electrons transported along electron transfer chain, releasing energy

  3. Energy used to actively transport protons from matrix into intermembrane space, creating electrochemical gradient

  4. Protons move down concentration gradient through ATP synthase, phosphorylating ADP to create ATP

  5. Electrons picked up by oxygen, which also picks up protons to form water
• Anaerobic respiration


  Respiration without oxygen, occurs in the cytoplasm in plants and microbes
• Anaerobic respiration


  • Produces ethanol and carbon dioxide in plants and microbes, produces lactate or lactic acid in animals
  • Reoxidizes NADH so glycolysis can continue
• Lactic acid can denature enzymes and other proteins, but allows some ATP production to continue
• Producers


  Green plants that can photosynthesize to make their own organic compounds
• Trophic level


  Each stage in a food web
• Between each trophic level, the majority of energy is lost due to respiration and excretion
• Biomass


  The mass of carbon within an organism, or the dry mass
• GPP (Gross Primary Production)


  The chemical energy stored in plant biomass in a given area or volume, the total energy from photosynthesis
• NPP (Net Primary Production)

  GPP minus the energy lost through respiration, the energy left to go towards biomass
• Net production in consumers

  N = I - F + R, where I is chemical energy in ingested food, F is energy lost in feces and urine, and R is respiratory losses
• Productivity rates are recorded in units of kilojoules per hectare per year
• The units standardize results to enable comparison between environments, and account for seasonal effects
• Nitrogen cycle


  Involves processes of ammonification, nitrification, nitrogen fixation, and denitrification
• Saprobiotic nutrition by microbes is essential for the nitrogen cycle
• Nitrogen fixation


  Conversion of atmospheric nitrogen gas into ammonia by nitrogen-fixing bacteria
• Nitrification


  Oxidation of ammonia into nitrites and then nitrates by nitrifying bacteria
• Denitrification


  Conversion of nitrates back into nitrogen gas by anaerobic denitrifying bacteria
• Phosphorus cycle


  Main store is phosphate ions in sedimentary rock, not as a gas in the atmosphere
• Mycorrhizae


  Fungal associations with plant roots that provide benefits for plant growth
• Phosphorus cycle


  1. Phosphate ions absorbed by plants, consumed by animals, returned to soil/oceans through excretion and decomposition

  2. Phosphate ions erode from sedimentary rock and deposited

  3. Fertilizers can add phosphorus to the cycle
• Natural fertilizers


  Animal manure, cheaper but less controlled mineral composition
• Artificial fertilizers


  Synthetic chemicals with exact mineral proportions, but more soluble and can leach into waterways
• Leaching of nitrogen fertilizers into waterways can cause eutrophication