Energy transfer in & between organisms

• Photosynthesis overview

  • thylakoid -> site of light dependent reaction
  • stroma -> site of light independent reaction
  • chlorophyll found of membrane of thylakoids

  structural adaptations: large SA, minimal leaves overlapping, thin

  • upper epidermis & waxy cuticle - thin & transparent
  • palisade mesophyll - has more chloroplasts
  • spongy mesophyll - air spaces for quick diffusion
  • phloem & xylem - transport glucose & water
• photosynthesis overview

  5 uses of glucose in plants:

  • respiration, protein synthesis, lipid synthesis, storage, cellulose

  3 main stages of photosynthesis:

  1. capturing light energy by chlorophyll
  2. light dependent reaction
  3. formation of ATP, NADP & O2
  4. electron flow created to cause photolysis
  5. light independent reaction
  6. protons used to make sugars & other organic molecules
• Light dependent reaction pt1

  oxidation = loss of hydrogen/loss of electrons

  reduction = gain of hydrogen/gain of electrons

  Making ATP:

  1. chlorophyll absorbs light energy
  2. electrons become excited & move to higher energy levels & leave chlorophyll - photoionisation
  3. electrons taken up by electron carrier molecule & passed along electron carrier chain via redox reactions
  4. chlorophyll oxidised & electron carrier reduced
  5. transfer chain found in thylakoid membrane
  6. energy lost between each transfer & used to make ATP
• chemiosmotic theory = mechanism of making ATP

  1. protons (H+) actively transported into thylakoid from stroma via proton pump carrier proteins
  2. energy for active transport comes from ETC
  3. H+ from active transport & photolysis creates an electrochemical gradient of protons across thylakoid membrane
  4. protons can only cross membrane via ATP synthase (stalked granules)
• Photolysis

  1. H2O splits using light energy via oxygen-evolving complex enzyme
  2. 2H2O -> 4H+ + 4e- + O2
  3. H+ & e- passed out at end of ETC are taken up by co-enzyme, oxidised NADP electron carrier
  4. H+ & e- reduce NADP into reduced NADP (NADPH)

  O2 is waste product & NADPH + ATP used in light independent reaction
• Light independent reaction - Calvin Cycle


  1. CO2 diffuses into leaf, dissolves in water & diffuses into stroma
  2. in stroma, CO2 fixes with 5C compound, ribulose biphosphate (RuBP) via ribulose biphosphate carboxylase (rubisco) enzyme to form unstable 6C compound
  3. CO2 & RuBP react again to form 2 molecules of 3C glycerate 3-phosphate (GP)
  4. reduced NADP reduces GP by adding H+ into 2 molecules of triose phosphate using ATP
  5. NADP reformed & goes back to LDR to be reduced again
  6. some triose phosphate converted organic substance but most used to reform ribulose biphosphate
• Factors affecting photosynthesis

  • limiting factor = factor that decreases/limits rate of photosynthesis
  • compensation point = CO2 released during respiration = CO2 taken in for photosynthesis
  • light intensity: proportional increase in rate
  • ↑ photons -> ↑chlorophyll ionised & ↑ ATP + NADP
  • optimal wavelength: PSI - 700nm & PSII - 680nm
  • CO2 concentration: increases until a plateau
  • temp: affects LIR (catalysed by enzymes)but not LDR
  • law of limiting factors: rate fo physiological process will be limited by the factor which is in shortest supply
• cellular respiration

  aerobic respiration: 6O2 + C6H12O6 -> 6H2O + 6CO2

  1. glycolysis (cytoplasm) = conversion of glucose to pyruvate
  2. link reaction (matrix) = pyruvate is converted to acetyl co-enzyme A
  3. kreb's cycle (matrix) = cycle of redox reactions that yield ATP & reduced NAD & FAD
  4. oxidative phosphorylation (cristae) = electron transfer chain using reduced NAD and FAD to form ATP and H2O
• Glycolysis

  1. phosphorylating glucose using ATP to make it more reactive by lowering its activation energy
  2. 2 molecules of triose phosphate made
  3. oxidation of triose phosphate to produce pyruvate
  4. net gain of ATP & reduced NAD
  5. 2ATP + NADH made per molecule of pyruvate formed
• Link reaction

  pyruvate + oxidised NAD + CoA -> Acetyl CoA + reduced NAD + CO2

  pyruvate actively transported into mitochondrial matrix

  reaction occurs twice

  1. pyruvate decarboxylated & dehydrogenated
  2. produces acetate
  3. Coenzyme A combines with acetate to form acetyl coenzyme A
  4. acetyl coenzyme A enters Kreb's cycle
• Kreb's cycle

  • net production per cycle: 3NAD, 1 reduced FAD, 1 ATP, 2CO2
  • Net production per glucose molecule: everything x 2

  A) decarboxylated & dehydrogenated

  B) oxoloacetate remade via substrate-level phosphorylation

  C) CoA combines with oxoloacetate to form citrate

  D) 2C -> 4C -> 6C

  E) 6C -> 5C -> 4C

  
• oxidative phosphorylation

  1. NAD & FADH2 oxidised
  2. H atoms donate e- to ETC
  3. ETC's lost energy for active transport of H+ across intermediate membrane
  4. electrochemical gradient formed
  5. H+ diffuses through ATP synthase (faciliated diffusion) which catalyses formation of ATP
  6. e- picked up at end of ETC by 1/2O2 & H+ to make water
  7. final e- acceptor