TOPIC 5

• Light dependent reaction


  1. Photoionisation

  2. Electron transfer chain

  3. Proton pumping

  4. Photophosphorylation

  5. NADP reduction
• Light independent reaction (Calvin cycle)

  1. CO2 reacts with RuBP

  2. Forming GP

  3. GP reduced to TP

  4. TP converted to organic substances

  5. TP used to regenerate RuBP
• describe and explain how temperature affects ROP

  1. As temperature increases, rate increases

  ○ Enzymes eg. rubisco gain kinetic energy

  ○ So more enzyme-substrate (E-S) complexes form

  2. Above an optimum temperature, rate decreases

  ○ Enzymes denature as H bonds in tertiary structure break

  ○ So fewer enzyme-substrate (E-S) complexes form
• describe and explain how light intensity affects ROP

  light intensity increases, rate increases

  ○ Light-dependent reaction increases (eg. more photoionisation of

  chlorophyll) so more ATP and reduced NADP produced

  ○ So light-independent reaction increases as more GP reduced to

  TP and more TP regenerates RuBP

  2. Above a certain light intensity, rate stops increasing

  ○ Another factor is limiting eg. temperature / CO2 concentration
• describe and exo,sin how CO2 CONC affects ROP

  1. As CO2 concentration increases, rate increases

  ○ Light-independent reaction increases

  ○ As more CO2 combines with RuBP to form GP

  ○ So more GP reduced to TP

  ○ So more TP converted to organic substances and more

  RuBP regenerated

  2. Above a certain CO2 concentration, rate stops increasing

  ○ Another factor is limiting eg. temperature / light intensity
• Agricultural practices


  Should increase rate of photosynthesis, leading to increased yield
• Profit from extra yield should be greater than costs (money & environmental costs)
• Isolating pigments with paper chromatography

  1. Crush leaves with solvent

  2. Draw pencil line on paper

  3. Add extract to line

  4. Stand paper in solvent

  5. Allow solvent to run up paper

  6. Remove before solvent reaches top
• Rf value


  Distance moved by spot / distance moved by solvent front
• Dehydrogenase


  Catalyses the reduction of NADP in the light-dependent reaction
• Measuring rate of dehydrogenase activity

  1. Extract chloroplasts

  2. Set up test tubes (control 1, control 2, standard, experiment)

  3. Shine light on tubes and time DCPIP decolourisation

  4. Rate = 1 / time taken

  
• Respiration produces ATP (to release energy)
• Stages of aerobic respiration

  • Glycolysis- cytoplasm (anaerobic)
  • Link reaction (mitochondrial matrix)
  • Krebs cycle (mitochondrial matrix)
  • Oxidative phosphorylation (inner mitochondrial membrane)
• Stages of anaerobic respiration

  • Glycolysis- cytoplasm
  • NAD regeneration- cytoplasm
• Glycolysis


  1. Glucose phosphorylated

  2. Hydrolysed to triose phosphate

  3. Oxidised to pyruvate
• Anaerobic respiration


  Pyruvate converted to lactate or ethanol, oxidising reduced NAD
• Anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration
• Aerobic respiration


  1. Glycolysis - cytoplasm (anaerobic)

  2. Link reaction - mitochondrial matrix

  3. Krebs cycle - mitochondrial matrix

  4. Oxidative phosphorylation - inner mitochondrial membrane
• Anaerobic respiration


  1. Glycolysis - cytoplasm

  2. NAD regeneration - cytoplasm
• Glycolysis


  1. Glucose phosphorylated to glucose phosphate

  2. Hydrolysed to 2 x triose phosphate

  3. Oxidised to 2 pyruvate
• explain what happens after glycolysis if respiration is anaerobic?

  • Pyruvate converted to lactate (animals & some bacteria) or ethanol (plants & yeast)
  • Oxidising reduced NAD → NAD regenerated
  • So glycolysis can continue (which needs NAD) allowing continued production of ATP
• what happens after glycolysis if respiration is aerobic

  Pyruvate is actively transported into the mitochondrial matrix
• Link reaction


  1. Pyruvate oxidised (and decarboxylated) to acetate

  2. CO2 produced

  3. Reduced NAD produced (picks up H)

  4. Acetate combines with coenzyme A, forming Acetyl Coenzyme A
• Krebs cycle

  1. Acetyl coenzyme A (2C) reacts with a 4C molecule

  2. Releasing coenzyme A

  3. Producing a 6C molecule that enters the Krebs cycle

  4. In a series of oxidation-reduction reactions, the 4C molecule is regenerated and: 2 x CO2 lost, Coenzymes NAD & FAD reduced, Substrate level phosphorylation (direct transfer of Pi from intermediate compound to ADP) → ATP
• Describe the process of Oxidative phosphorylation

  1. Reduced NAD/FAD oxidised to release H atoms → split into protons (H+) and electrons (e-)

  2. Electrons transferred down electron transfer chain (chain of carriers at decreasing energy levels)

  3. Energy released by electrons used in the production of ATP from ADP + Pi (chemiosmotic theory)

  4. In matrix at end of ETC, oxygen is final electron acceptor (electrons can't pass along otherwise)
• Give examples of Other respiratory substrates

  • Fatty acids from hydrolysis of lipids → converted to Acetyl Coenzyme A
  • Amino acids from hydrolysis of proteins → converted to intermediates in Krebs cycle
• Measuring aerobic respiration using a respirometer (measuring oxygen uptake 


  1. Add a set mass of single-celled organism eg. yeast to a set volume / concentration of substrate eg. glucose

  2. Add a buffer to keep pH constant

  3. Add a chemical that absorbs CO2 eg. sodium hydroxide

  4. Place in water bath at a set temperature and allow to equilibrate

  5. Measure distance moved by coloured liquid in a set time

  
• Why the liquid moves in a respirometer

  • Organisms aerobically respire → take in O2
  • CO2 given out but absorbed by sodium hydroxide solution
  • So volume of gas and pressure in container decrease
  • So fluid in capillary tube moves down a pressure gradient towards organism

  
• Why the respirometer apparatus is left open for 10 minutes?


  -Allow apparatus to equilibrate

  - Allow for overall pressure expansion/change throughout

  -Allow respiration rate of organisms to stabilise
• Why the respirometer apparatus must be airtight?


  -Prevent air entering or leaving

  ● Would change volume and pressure, affecting movement of liquid
• More accurate way to measure volume of gas

  Use a gas syringe
• Calculating rate of respiration from a respirometer

  1. Calculate volume of O2 / CO2 consumed / released (calculate area of a cylinder)

  2. Divide by mass of organism and time taken
• Measuring anaerobic respiration using a respirometer (carbon dioxide release )


  1. Repeat experiment as above but remove chemical that absorbs CO2

  2. Make conditions anaerobic, for example: Layer of oil / liquid paraffin above yeast → stop O2 diffusing in, Add a chemical that absorbs O2, Leave for an hour to allow O2 to be respired and used up

  
• Why the liquid moves in an anaerobic respirometer

  • Yeast anaerobically respire → release CO2
  • So volume of gas and pressure in container increase
  • So fluid in capillary tube moves down a pressure gradient away from organism
• Why the anaerobic respirometer apparatus is left for an hour after the culture has reached a constant temperature?


  to allow time for the oxygen to be used/respired
• Measuring respiration using redox indicator dyes

  1. Add a set volume of organism eg. yeast and a set volume of respiratory substrate eg. glucose to tubes

  2. Add a buffer to keep pH constant

  3. Place in water bath at a set temperature and allow to equilibrate for 5 mins

  4. Add a set volume of methylene blue, shake for a set time (do not shake again)

  5. Record time taken for colour to disappear in tube
• Examples of variables that could be controlled

  • Volume of single-celled organism
  • Volume / conc. / type of respiratory substrate
  • Temperature (with a water bath)
  • pH (with a buffer)
  • Volume of redox indicator (only control)
• Why leave tubes in the water bath for 5 minutes?


  • to allow the solutions to equilibrium and reach the same temperature as the water bath
• describe a control experiment and why it would be done

  • Add methylene blue to boiled / inactive / dead yeast (boiling denatures enzymes)
  • All other conditions the same
  • To show change is due to respiration in organisms

  
• Why you must not shake tubes containing methylene blue?


  Shaking would mix solution with oxygen

  ● Which would oxidise methylene blue / cause it to lose its electrons

  ● So methylene blue would turn back to its original blue colour