TOPIC 5 - ENERGY TRANSFERS

• Location of light dependent reaction

  • Thylakoid membranes of chloroplast
• Location of light independent reaction

  • Stroma of chloroplast
• Chloroplast structure


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• Thylakoid membranes

  • Folded membranes containing photosynthetic proteins (chlorophyll)
  • embedded with transmembrane electron carrier proteins
  • involved in the LDRs
• Chlorophyll

  • Located in proteins on thylakoid membranes
  • mix of coloured proteins that absorb light
  • different proportions of each pigment lead to different colours on leaves
• Advantage of many pigments

  • Each pigment absorbs a different wavelength of visible light
  • many pigments maximises spectrum of visible light absorbed
  • maximum light energy taken in so more photoionisation and higher rate of photosynthesis
• Light-dependent reaction (LDR)

  • First stage of photosynthesis
  • occurs in thylakoid membranes 
  • uses light energy and water to create ATP and reduced NADP for LIR
  • involves photoionisation of chlorophyll, photolysis and chemiosmosis
• Photolysis


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• Products of photolysis


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• Photoionisation of chlorophyll

  • Light energy absorbed by chlorophyll excites electrons so they move to a higher energy level and leave chlorophyll
  • some of the energy released is used to make ATP and reduced NADP
• Chemiosmosis

  • Electrons that gained energy move along a series of electron carriers in thylakoid membrane
  • release energy as they go along which pumps proteins across thylakoid membrane
  • electrochemical gradient made
  • protons pass back across via ATP synthase enzyme producing ATP down their conc. gradient
• What happens to protons after chemiosmosis

  • Combine with co-enzyme NADP to become
  • reduced NADP reduced NADP used in LIR
• Products of LDR

  • ATP (used in LIR)
  • reduced NADP (used in LIR)
  •  oxygen (used in respiration / diffuses out stomata)
• Light independent reaction (LIR)

  • Calvin cycle
  • uses CO2,
  • reduced NADP and ATP to form hexose sugar
  • occurs in stroma which contains the enzyme Rubisco
  • temperature-sensitive
• Calvin cycle


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• RuBP

  • Ribulose Bisphosphate
  • 5-carbon molecule
• GP

  • Glycerate-3-phosphate
  • 3-carbon molecule
• TP

  • Triose phosphate
  • 3-carbon molecule
• Producing hexose sugar in LIR

  • Takes 6 cycles
  • glucose can join to form disaccharides (sucrose) or polysaccharides (cellulose)
  • can be converted to glycerol to combine with fatty acids to make lipids
• Limiting factor

  • A factor which, if increased, the rate of the overall reaction also increases
• Limiting factors of photosynthesis

  • Light intensity
  • CO2 concentration
  • temperature
• How light intensity limits photosynthesis


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• How temperature limits photosynthesis


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• How CO2 concentration limits photosynthesis


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• Agricultural practices to maximise plant growth

  • Growing plants under artificial lighting to maximise light intensity
  • heating in greenhouse to increase temperature
  • burning fuel to release CO2
• Benefit of agricultural practices for plant growth

  • Faster production of glucose -> faster respiration
  • more ATP to provide energy for growth e.g. cell division + protein synthesis
  • higher yields so more profit
• Products of LIR

  • Hexose sugar
  • NADP - used in LDR
• Stages of aerobic respiration


  1)Glycolysis

  2) Link reaction

  3) Krebs cycle

  4) Oxidative phosphorylation
• Location of glycolysis

  • Cytoplasm
• Glycolysis

  • Substrate level phosphorylation - 2 ATP molecules add 2 phosphate groups to glucose
  • glucose phosphate splits into two triose phosphate (3C) molecules
  • both TP molecules are oxidised (reducing NAD) to form 2 pyruvate molecules (3C)
  • releases 4 ATP molecules
• Coenzymes

  • A molecule which aids / assists an enzyme
  • NAD and FAD in respiration both gain hydrogen to form reduced NAD (NADH) and reduced FAD (FADH)
  • NADP in photosynthesis gains hydrogen to form reduced NADP (NADPH)
• Products of glycolysis

  • Net gain of 2 ATP
  • 2 reduced NAD
  • 2 pyruvate molecules
• How many ATP molecules does glycolysis produce

  • 2 ATP molecules used to phosphorylate glycose to glucose phosphate
  • 4 molecules generated in oxidation of TP to pyruvate 
  • net gain 2 ATP molecules
• Location of the link reaction

  • mitochondria matrix
• Link reaction


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• Products of the link reaction per glucose molecule

  • 2 acetylcoenzyme A molecules 
  • 2 carbon dioxide molecules released
  • 2 reduced NAD molecules
• Location of the Krebs cycle

  • Mitochondrial matrix
• Krebs cycle


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• Products of the Krebs cycle per glucose


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• Location of oxidative phosphorylation

  • Cristae of mitochondria