Unit 5 bio

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


  • Thylakoid membrane and stacks (grana) where light dependent reactions occur
  • Stroma where light independent reactions occur
  • Inner and outer membranes
• Light dependent reactions


  1. Photolysis (splitting of water)

  2. Photoionization of chlorophyll

  3. Chemiosmosis (proton gradient and ATP synthesis)
• Photolysis


  Light energy splits water into oxygen, electrons and protons
• Photoionization of chlorophyll


  Light energy excites chlorophyll electrons, causing them to be released
• Chemiosmosis


  Protons are pumped across the thylakoid membrane, creating a gradient that drives ATP synthesis
• Light dependent reactions produce ATP and reduced NADP
• Light independent reactions (Calvin cycle)

  1. Carbon dioxide reacts with RuBP

  2. GP is reduced to TP using ATP and NADPH

  3. TP is used to regenerate RuBP or form hexose sugars
• Rubisco


  Key enzyme in the Calvin cycle
• Limiting factors can reduce the rate of photosynthesis (light, CO2, temperature)
• Aerobic respiration has 4 stages: glycolysis, link reaction, Krebs cycle, oxidative phosphorylation
• Glycolysis


  1. Glucose is phosphorylated

  2. Triose phosphates are oxidised to pyruvate, producing ATP and NADH
• Link reaction


  Pyruvate is oxidised to acetyl CoA, releasing CO2 and producing NADH
• Krebs cycle


  1. Acetyl CoA combines with oxaloacetate

  2. Series of redox reactions, producing ATP, NADH, FADH2, and CO2
• Oxidative phosphorylation


  1. NADH and FADH2 donate electrons to electron transport chain

  2. Proton gradient drives ATP synthesis by ATP synthase
• Oxidative phosphorylation produces the majority of ATP in aerobic respiration
• 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


  1. Glycolysis occurs as usual

  2. Pyruvate reduced to form lactate or ethanol and CO2

  3. Reduced coenzymes re-oxidized to NAD+ to allow glycolysis to continue
• Anaerobic respiration


  • Produces lactic acid or ethanol, which can be harmful 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

  Chemical energy in ingested food - chemical energy lost in feces/urine - respiratory losses
• Productivity rates are recorded in units of kilojoules per hectare per year
• The units include per unit area to standardize results, and per year to account for seasonal effects
• Nitrogen cycle


  Involves processes of nitrogen fixation, nitrification, ammonification, and denitrification
• Nitrogen is essential for proteins, ATP, and nucleic acids
• Key processes in the nitrogen cycle

  • Nitrogen fixation
  • Nitrification
  • Ammonification
  • Denitrification
• Saprobiotic nutrition


  Microbes feeding on dead plant matter or waste
• Denitrifying bacteria convert nitrates to nitrogen gas under anaerobic conditions
• Phosphorus cycle


  Phosphorus is stored mainly in sedimentary rocks, not as a gas
• Mycorrhizae


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


  1. Phosphate ions in oceans/soil absorbed by plants

  2. Animals consume plants, excrete phosphate ions

  3. Decomposition releases phosphate ions

  4. Sedimentation forms phosphate-containing rocks

  5. Erosion releases phosphate ions
• Fertilizers


  Added to soils to replace minerals removed when crops are harvested