Energy Transfers In and Between Organisms

• Oxidative Phosphorylation 1

  1. The reduced coenzymes - NADH and FADH move to the inner mitochondrial membrane where they release their hydrogens in the form of protons (H+) and electrons
  2. The electrons enter the electron transfer chain (attached to the cristae) at a high energy level and move, between carriers, to lower energy levels - this releases energy
  3. This energy is used to pump protons from the matrix, across the cristae and into the intermembranal space, thus creating a chemiosmotic gradient
• Oxidative phosphorylation 2

  1. The protons move down their gradient through channel proteins embedded in the inner membrane. In doing so, they activate ATP synthase (also embedded in the inner membrane) which catalyse the reaction : ADP + Pi —> ATP
  2. Both the electrons which reach the end of the electron transfer chain, and the protons - which have diffused back into the matrix need to be removed for process to continue.
  3. Oxygen does this by reacting with them to form water. For this reason, oxygen is the final electron acceptor.
• Glycolysis - Glucose -> Glucose phosphate


  2ATP -> 2ADP + Pi
• Glycolysis - Triose phosphate -> pyruvate


  Oxidised

  NAD reduced to NADH

  2ADP + Pi -> 2ATP

  if oxygen is present, pyruvate is actively transported into mitochondrial matrix
• Pyruvate

  Reduced to lactate in animals/bacteria

  Reduced to ethanol in plants/yeast

  NADH is oxidised

  NAD is regenerated to allow glycolysis to continue
• Link reaction - Pyruvate (3C) -> Acetate (2C)


  NAD reduced to NADH

  Oxidised

  Decarboxylated
• Link reaction - Acetate (2C) -> Acetyl coenzyme A


  Conenzyme A joins
• Krebs cycle - Acetyl coenzyme A - 6C compound 


  Coenzyme A goes back to link reaction

  acetyl coenzyme A joins with 4C compound
• Krebs cycle - 6C -> 5C


  Decarboxylated

  Oxidised

  NAD reduced to NADH
• Krebs cycle - 5C -> 4C


  Decarboxylated

  ADP + Pi -> ATP

  2NAD reduced to 2NADH

  FAD reduced to FADH
• Other respiratory substrates - lipids


  Glycerol converted to triose phosphate in glycolysis

  Fatty acid chains are broken into 2Cs and are converted into acety coenzyme A

  Hydrogens which remain can be used to form the chemiosmotic gradient
• Other respiratory substrates- proteins


  Hydrolysis of peptide bonds to release amino acid

  Amine group removed

  3C - pyruvate

  4C, 5C - Krebs cycle
• Light dependent stage 1

  Light is absorbed by chlorophyll, causing it to become photoionised

  Electrons are excited and move to a higher energy level

  The excited electrons are replaced by those from photolysis and enter the electron transfer chain attached to the thylakoid membrane

  As the electron moves down the electron transfer chain, energy is released used to pump the protons produced in photolysis from the stroma to the thylakoid, creating a chemiosmotic/electrochemical gradient
• Light dependent stage 2

  The protons diffuse back into the stroma through a channel protein causing ATP synthase to catalyse the reaction : ADP + Pi -> ATP

  The electron at the end of the ETC and protons bind with NADP to form NADPH2 which is the final electron acceptor
• Light independent stage - ribulose bisphosphate + CO2 -> 2 glycerate 3 phosphate


  Carbon dioxide combines with ribulose bisphophate to form 2x glycerate 3 phosphate.

  Rubisco catalyses the reaction
• Light independent stage - 2 glycerate 3 phosphate -> 2 triose phosphate


  Glycerate 3 phosphate is reduced to triose phosphate using the reduced 2NADP and energy from the hydrolysis of 2ATP
• Light independent stage - triose phosphate -> RuBP


  Triose phosphate is used to make useful organic substances including glucose and the rest is used to regenerate RuBP

  ATP -> ADP + Pi
• Energy flow through ecosystems

  Only 1-3% of light is used

  • Light misses the chloroplast
  • Some light is of the wrong wavelength
  • Other limiting factors
  • Energy lost as heat
• Gross primary productivity


  Chemical energy in the biomass of the plant

  GPP = NPP + R
• Net primary productivity


  Chemical energy in the biomass of the plant after respiratory losses
• Net productivity 


  NP = I - (R + F)

  Used for growth/reproduction and available to the next trophic level
• Eutrophication

  Soluble fertilisers undergo leaching whereby mineral ions are washed off fields and into waterways

  This can cause algal blooms at the surface of lakes which block light from penetrating the water

  Aquatic plants will die and this decrease in photosynthesis will reduce the oxygen concentration in the water

  This will increase the number of aerobic saprobionts which further declines the concentration of oxygen

  Aquatic animals will now die leading to even more aerobic saprobionts and the concentration of oxygen in the lakes becomes so low that the conditions in the lakes can be considered anaerobic