Energy for Biological Processes

• Photosynthesis reaction


  1. Carbon dioxide combines with water to form glucose and oxygen

  2. Glucose is used in respiration to produce energy

  3. Oxygen is released from the plant through the stomata
• Chloroplast structure


  • Contains fluid-filled sacs called thylakoids
  • Thylakoids are stacked up like pancakes to form grana
  • Grana are connected by lamellae
  • Gel-like substance surrounding thylakoids is called the stroma
  • Thylakoids provide a large surface area to absorb light
• Photosystems


  Consist of pigment molecules attached to proteins within the thylakoid membrane
• Photosynthetic pigments


  • Chlorophyll a
  • Chlorophyll b
  • Carotene
• Photosystem I (PSI)


  Absorbs light at a wavelength of 700 nm
• Photosystem II (PSII)


  Absorbs light at a wavelength of 680 nm
• Light-Dependent Reaction (LDR)


  1. Light energy is absorbed by PSII

  2. Electrons in PSII become excited and move to higher energy state

  3. Electrons passed along electron transport chain to PSI

  4. Water photolysis replaces electrons lost from PSII

  5. Electron transport drives proton gradient across thylakoid membrane

  6. Protons flow through ATP synthase to phosphorylate ADP to ATP, called chemiosmosis

  7. Light absorbed by PSI excites electrons which are passed to NADP to form NADPH
• Non-cyclic photophosphorylation


  Process where electrons move through both photosystems, producing ATP and NADPH
• Cyclic photophosphorylation


  Process where electrons cycle through PSI, producing only ATP
• Light-Independent Reactions (Calvin Cycle)

  1. Carbon fixation: CO2 added to RuBP, which forms a 6-C . This forms 2 3-carbon GP, which is catalysed by RuBiSCO

  2. Reduction: GP converted to Triose phosphate using ATP and NADPH

  3. Regeneration: Triose phosphate converted back to RuBP using ATP
• Rubisco


  Enzyme that catalyses the carbon fixation reaction
• For every 6 molecules of GALP, 1 is used to produce organic molecules and 5 are used to regenerate RuBP
• Organic molecules synthesised from GALP and GP

  • Glucose
  • Amino acids
  • Glycerol
  • Fatty acids
• Investigating leaf pigments using chromatography

  1. Extract pigments from leaves

  2. Apply extract to TLC plate

  3. Place TLC plate in solvent tank

  4. Pigments separate based on solubility

  5. Identify pigments by calculating Rf values
• Optimum conditions for photosynthesis

  • High light intensity
  • Optimal temperature around 25°C
  • High CO2 concentration (up to 0.4%)
• As temperature increases


  Rate of photosynthesis increases
• As light intensity increases

  Rate of photosynthesis increases
• As CO2 concentration increases

  Rate of photosynthesis increases
• Limiting factors


  Factors that determine the rate of photosynthesis: temperature, light intensity, CO2 concentration
• Rate of photosynthesis can be calculated by measuring the volume of oxygen produced over time