Topic 5 – Energy Transfers In & Between Organisms

• Photosynthesis


  Reaction in which light energy is used to produce glucose in plants
• Photosynthesis


  1. Requires water and carbon dioxide

  2. Products are glucose and oxygen

  3. Two stages: light dependent and light independent

  4. Rate determined by carbon dioxide concentration, light intensity, and temperature
• Chloroplasts

  • Site of photosynthesis
  • Contains stacks of thylakoid membranes called grana which provides a large surface area for the attachment of chlorophyll, electrons and enzymes
  • Network of proteins in the grana hold the chlorophyll in a specific manner to absorb maximum light
  • Granal membrane has ATP synthase channels allowing ATP synthesis and is selectively permeable establishing a proton gradient
  • Contain DNA and ribosomes allowing protein synthesis needed in light dependent reaction

  
• Light Dependent Reaction


  1. Photons hit chlorophyll in PSII causing electron excitation and photolysis (splitting of water)

  2. Excited electron moves down electron transport chain, pumping protons to create proton gradient

  3. Electron used to reduce NADP forming NADPH

  4. Proton gradient drives ATP synthesis through ATP synthase
• Light Independent Reaction (Calvin Cycle)

  1. Carbon dioxide fixation by Rubisco

  2. Reduction of 3-carbon glycerate-3-phosphate to triose phosphate using NADPH and ATP

  3. Regeneration of 5-carbon ribulose bisphosphate using ATP

  4. Production of organic molecules like glucose from triose phosphate

  
• Aerobic respiration

  Splitting of respiratory substrate to release carbon dioxide and energy
• Anaerobic respiration

  Respiration in the absence of oxygen
• Respiration


  1. Glycolysis in cytoplasm

  2. Link reaction in mitochondria

  3. Krebs cycle in mitochondrial matrix

  4. Oxidative phosphorylation in mitochondria

  
• Only around 10% of chemical food energy is passed on between organisms in the food chain
• Percentage efficiency of energy transfer

  Calculated as (Energy content of consumers)/(Energy content of resources) x 100
• Biomass


  Measured in mass of carbon or dry mass of tissue per given area per given time
• Calorimetry


  Measuring energy content of biomass by burning in a bomb calorimeter
• Net primary productivity (NPP)

  Rate of energy transfer into organic molecules in new plant biomass, after respiratory losses
• Gross primary productivity (GPP)


  Rate of energy incorporation into organic molecules in plants through photosynthesis
• NPP


  GPP - Respiration
• Net production of consumers (N)


  I - (F+R), where I is energy in ingested food, F is energy lost in faeces/urine, and R is respiratory losses
• Nitrogen Cycle

  1. Ammonification

  2. Nitrification

  3. Denitrification

  4. Nitrogen fixation
• Ammonification


  Breakdown of organic matter to ammonia by saprobionts
• Nitrification

  Conversion of ammonia to nitrate by nitrifying bacteria
• Denitrification


  Conversion of nitrate to nitrogen gas by denitrifying bacteria
• Nitrogen fixation


  Conversion of nitrogen gas to ammonia by nitrogen-fixing bacteria
• Phosphorus Cycle


  • Plants take up phosphate ions from soil
  • Phosphate released from weathering of rocks and decay of bones/shells/excreta
• Mycorrhizae

  Associations between fungi and plant roots that facilitate water and ion uptake
• Nitrogen fertilisers increase crop yields but have negative environmental effects like reducing biodiversity, leaching, and eutrophication
• Leaching


  Mineral ions like nitrate dissolving in rainwater and being carried to rivers and lakes
• Eutrophication

  Rapid growth of algae due to excess nutrients, leading to ecosystem decay and oxygen depletion