Topic 5 – Energy Transfers In & Between Organisms.

• 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


  1. Reduced coenzymes release hydrogen

  2. Electrons transported along electron transfer chain

  3. Energy used to transport protons into intermembrane space

  4. Protons move through ATP synthase

  5. ATP synthase phosphorylates ADP to create ATP

  6. Electrons picked up by oxygen to form water
• Oxidative phosphorylation is the final step and this is very similar to chemiosmosis in the light dependent reaction of photosynthesis
• Oxidative phosphorylation is where most of the ATP is produced
• Anaerobic respiration is without oxygen and it only occurs in the cytoplasm in plants and microbes
• Anaerobic respiration


  1. Glycolysis occurs as usual

  2. Pyruvate is reduced to form lactate

  3. Reduced coenzymes are re-oxidized to NAD

  4. Ensures glycolysis can continue
• Anaerobic respiration produces ethanol and carbon dioxide in plants and microbes, and lactate or lactic acid in animals
• Anaerobic respiration is to re-oxidize NAD so that glycolysis can continue to occur
• The downside of anaerobic respiration is lactic acid is acidic so it can denature enzymes and other proteins
• Microbes produce ethanol and carbon dioxide in anaerobic respiration to ensure glycolysis can still continue
• Producers


  Green plants that can photosynthesize to use light energy to make their own organic compounds
• Between each trophic level in a food web, the majority of energy is lost due to respiration and excretion
• Biomass


  The mass of carbon within an organism or the dry mass