Topic 5 - Energy transfers in and between organsims

• Chloroplasts


  Organelles in plant cells where photosynthesis occurs

  
• Photosynthesis


  1. Light-dependent reaction

  2. Light-independent reaction

  
• Thylakoid membrane


  Folded membranes which contain photosynthetic proteins (chlorophyll) and embedded, transmembrane electron carrier proteins which are both involved in light-dependent reaction

  
• Stroma


  Fluid centre which contains enzymes involved in the light-independent reaction

  
• Inner and outer membrane

  Controls what can enter and leave the organelle (think plasma membranes)
• Photosynthetic pigments


  • Chlorophyll a
  • Chlorophyll b
  • Carotene
  • Xanthophyll
  • Phaeophytin

  
• Chlorophyll


  • Located in the photosystems on the thylakoid membrane
  • A mix of coloured proteins that can absorb light

  
• Chlorophyll a is the most abundant photosynthetic pigment
• Different proportions of each pigment in leaves gives them slightly different colours
• Each pigment absorbs a different wavelength of visible light, maximising the spectrum of visible light absorbed
• Light-dependent reaction


  1. Photoionisation of chlorophyll

  2. Photolysis

  3. Chemiosmosis
• Photoionisation


  Light energy is absorbed by chlorophyll which results in electrons becoming excited so they can move up an energy level to leave the chlorophyll
• Photolysis


  Light energy is absorbed by chlorophyll and splits water into oxygen, H+ and e-
• Chemiosmosis


  The electrons that gained energy and left the chlorophyll move along a series of electron-carrier proteins embedded within the thylakoid membrane, releasing energy which is used to pump protons across the chloroplast membranes, creating an electrochemical gradient. The protons then pass back through ATP synthase, producing ATP.

  
• Light-independent reaction (Calvin cycle)

  1. Carbon dioxide reacts with RuBP to form GP

  2. GP is reduced to TP using ATP and reduced NADP

  3. Some carbon from TP leaves the cycle to form organic substances, the rest is used to regenerate RuBP

  
• RuBP


  Ribulose bisphosphate
• GP


  Glycerate 3-phosphate
• TP


  Triose phosphate
• Rubisco


  Enzyme that catalyses the reaction of carbon dioxide with RuBP
• Limiting factors can reduce the rate of photosynthesis, such as temperature, carbon dioxide concentration or light intensity

  
• Techniques to remove limiting factors

  • Growing plants under artificial lighting
  • Heating a greenhouse
  • Burning fuel to release more carbon dioxide
• Cost-effective


  When the extra growth from photosynthesis is worth the cost of the techniques used

  
• Chlorophyll absorbs light, leading to photoionisation of chlorophyll, photolysis and chemiosmosis
• The light-dependent reaction results in the production of ATP and reduced NADP to be used in the light-independent reaction
• The light-independent reaction uses ATP and reduced NADP to reduce GP to TP, with carbon from TP contributing to making organic substances and regenerating RuBP

  
• Chemiosmosis links to transport across cell membranes


  Active transport and facilitated diffusion
• Chlorophyll is a protein


  Links to protein structure and function
• The role of protons (H+) in chemiosmosis


  Links to inorganic ions in biological molecules
• Substrate-level phosphorylation


  The glucose has 2 phosphate groups added to it from 2 ATP molecules, making it unstable and splitting into two 3-carbon compounds, triose phosphate

  
• Glycolysis


  The sugar-splitting process that occurs in the cytoplasm in both anaerobic and aerobic respiration
• Aerobic respiration


  Occurs in 4 stages: glycolysis, link reaction, Krebs cycle, oxidative phosphorylation
• Link reaction


  Converts pyruvate into acetyl CoA in the mitochondrial matrix

  
• Krebs cycle


  A series of oxidation-reduction reactions in the mitochondrial matrix that generates reduced coenzymes, ATP and carbon dioxide

  
• Oxidative phosphorylation


  Electrons are passed down the electron transport chain in the inner mitochondrial membrane, releasing energy to pump protons into the intermembrane space, creating an electrochemical gradient. The protons then flow back through ATP synthase, producing ATP.

  
• Anaerobic respiration


  Respiration that occurs in the absence of oxygen, where pyruvate is reduced to form ethanol and carbon dioxide (in plants/microbes) or lactate (in animals)

  
• Oxidative phosphorylation


  1. Transfer of electrons down the electron transfer chain

  2. Movement of protons across the inner mitochondrial membranes

  
• Electrochemical gradient


  Movement of H+ back into the matrix via ATP synthase making ATP
• Chemiosmosis


  Movement of H+
• Final electron acceptor


  Oxygen combines with electrons and protons to form water
• Anaerobic respiration


  1. Pyruvate reduced to form ethanol and carbon dioxide (in plants and microbes) or lactate (in animals)

  2. Oxidises NAD so it can be reused in glycolysis

  3. Ensures ATP is continued to be produced