PHOTOSYNTHESIS

• Adaptations of plants for photosynthesis

  • Large surface area
  • Minimal overlapping to avoid blocking sunlight
  • Thin, keeping diffusion distances short
  • Transparent cuticle and epidermis that allow light through
  • Long narrow upper mesophyll cell packed with chloroplasts
  • A lot of stomata for gaseous exchange
  • Stomata open and close in response to light intensity
  • Xylem and phloem
• Photosynthesis


  6CO2 + 6H2O —> C6H12O6 + 6O2
• Stages of photosynthesis


  • Capturing of light energy by chlorophyll
  • The light-dependant reaction where water splits into protons (H) electrons and oxygen. The products are ATP, reduced NADP, and oxygen
  • The light- independent reaction where sugars and inorganic molecules are produced using the protons
• Chloroplasts


  • Grana contain chlorophyll, this is where the light-dependant stage takes place
  • The stroma is where the light=independent stage takes place
• Light dependant reaction


  1. 2H2O —> 4H+ + 4e- + O2

  2. Light energy raises the energy level of the electrons in the chlorophyll. They move out of the chlorophyll, making it ionised (photoionization) and move to an electron carrier which becomes reduced. They move through the electron carriers through a series of oxidation-reduction reactions, and the electrons lose energy at each stage. This energy is used to combine an inorganic phosphate molecule with an ADP molecule to form an ATP

  3. Chemiosmotic theory is the mechanism by which ATP is produced. Protons (H) are pumped from the stroma using proton pumps in the thylakoid membrane. The energy released during the photolysis of water is used to drive this

  4. The photolysis of water also produces protons which increases their concentration in the thylakoid space, maintaining a concentration gradient with a low concentration of protons in the stroma

  5. Stalked granules are the ATP synthase channel proteins that the protons can cross the thylakoid membrane into the stroma through. As they pass through them, the structure of the enzyme changes which catalyses the combination of ADP with inorganic phosphate to form ATP
• Light dependant reactions


  • Large surface area of the thylakoid membranes
  • Proteins in the grana hold the chlorophyll in a very precise manner for maximum light absorption
  • ATP synthase channels in the granal membranes which catalyse the production of ATP
• Chloroplasts contain DNA and ribosomes so can make some of the proteins involved in the reaction easily
• Main components in the Light dependant reaction

  • NADP
  • ADP
  • Pi
  • Water
• The chlorophyll has a lot of different pigments in order to accept more wavelengths of light for photosynthesis
• Light independent reaction


  1. CO2 diffuses into the leaf, dissolves in water, and then diffuses into the stroma of the chloroplast

  2. It reacts with ribulose bisphosphate (RuBP), catalysed by ribulose bisphosphate carboxylase (rubisco)

  3. Two glycerate 3-phosphate molecules are formed

  4. Reduced NADP reduces this into two triose phosphate (TP) using energy from ATP

  5. The NADP is re-formed and goes back to the light-dependent reaction to be reduced again

  6. Some TP molecules are converted to organic substances for the use of the plant

  7. Most are used to regenerate ribulose bisphosphate using ATP from the light-dependent reaction
• Stroma


  • All needed enzymes are found in the stroma, which is membrane bound in the chloroplast
  • Stroma fluid surrounds the grana, so the products of the light-dependent reaction are easily available
  • Contains DNA and ribosomes so needed proteins are easily manufactured
• Light compensation point


  The point where the CO2 released during respiration equals that taken up during photosynthesis
• Measuring the rate of photosynthesis

  1. Measure the volume of oxygen produced by the apparatus

  2. Ensure there are no air bubbles

  3. The water bath is used to maintain a constant temperature

  4. Potassium hydrogen carbonate solution is used to provide a source of CO2

  5. Oxygen released by the plant during photosynthesis collects in the funnel end of the capillary tube; it is drawn gently and measured

  6. The process is repeated four or five times

  7. Before opening the light source, the apparatus is left in dark for two hours
• Respiration


  The process by which plants convert stored energy into a form that they can use, releasing carbon dioxide in the process.
• Photosynthesis


  The process by which plants convert light energy into chemical energy, taking in carbon dioxide and releasing oxygen in the process.
• Light compensation point


  The point at which the amount of carbon dioxide released during respiration equals the amount taken in during photosynthesis, resulting in a net balance of carbon dioxide.
• Importance of the light compensation point

  Understanding the light compensation point is important for understanding the conditions under which plants are able to grow and thrive, and for developing strategies to optimize these conditions to improve crop yields and reduce waste.
• Breakdown


  The process of breaking down large lipid molecules into smaller fatty acids and monoglycerides, facilitated by bile salts in the small intestine.
• Absorption


  The process of taking in smaller, broken-down molecules (fatty acids and monoglycerides) into the bloodstream through the walls of the small intestine, following the breakdown of lipids.
• Bile salts


  Molecules found in the small intestine that assist in the emulsification of lipids, increasing the lipid surface area for breakdown by enzymes like lipase.
• Emulsification


  The process of breaking down large lipid droplets into smaller, more manageable particles, increasing the surface area of lipids for enzymatic breakdown.
• Draw chloroplast structure:

  
• What are thylaokoid membranes?

  Folded membranes which contain chlorophyll and electron carrier proteins are embedded within these membranes which are both involved in LDR
• What is stroma?


  fluid centre which contains enzymes involved in LIR
• Purpose of inner and outer membrane?

  control what can enter and leave organelle
• Where does LDR occur?

  Thylakoid membrane or Grana/GRANUM
• Where does LIR occur?

  Stroma
• What is used to create ATP and reduced NADP in light-dependent reaction?

  Light energy and water
• What are the 4 key stages of light-dependent reaction?

  Photolysis

  Photoionisation

  Chemiosmosis

  Production of ATP AND reduced NADP (used for LIR)
• What does PHOTO and LYSIS refer to in photolysis of water?

  Photo = light

  Lysis = splitting
• What happens in photolysis of water?

  Light energy absorbed by chlorophyll

  splits water into oxygen, H+ and e-
• Equation of photolysis?


  H20 -> 1/2 O2 + 2e- + 2H+
• What happens to H+, e- and oxygen in photolysis?

  H+ picked up by NADP to form NADPH and used in LIR

  e- passed along ETC

  oxygen used for respiration or diffuses out of leaf through stroma
• What is photoionisation of chlorophyll?

  Light energy absorbed by chlorophyll excites electrons and raises them up an energy level to leave chlorophyll (chlorophyll = ionised by light)
• What happens to some of the energy from released electrons in photoionisation of chlorophyll?

  used to make ATP and reduced NADP in chemiosmosis
• What happens to the electrons that have left chlorophyll?

  move along a series of proteins embedded within the thylakoid membrane
• When electrons pass photosystems and release energy - what does it do to the H+ in stromas?

  pumps protons across the chloroplast membrane from stroma to thylakoid lumen
• More H+ in thylakoid membrane leads to a concentration gradient being created. What is this called?

  electrochemical gradient
• This electrochemical gradient enables protons to move through facilitated diffusion down concentration gradient, and pass through enzyme called?

  ATP synthase
• When protons pass through ATP synthase, what happens?

  ADP + pi -> ATP

  production of ATP