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• Photosynthesis


  A process which involves a series of enzyme controlled chemical reactions
• Autotrophs


  Able to make their own food, often green plants (and some bacteria) that carry out photosynthesis using the green pigment called chlorophyll which is found in chloroplasts
• Chloroplast


  • Thylakoid membrane contains chlorophyll (green pigment that absorbs light)
  • Granum (stacks of thylakoids)
  • Stroma (liquid matrix where light-independent reactions occur)
  • Starch granules (broken down to form glucose) are present in the stroma
• Photosynthesis


  1. Light-dependent reactions

  2. Light-independent reactions
• Photosynthesis can be summarized as: 6 H2O + 6 CO2 ↔ C6H12O6 + 6 O2
• Light-dependent reactions


  1. Solar energy energises electrons in thylakoid membranes

  2. Electrons passed down electron transport chain to make ATP

  3. Water split to hydrogen and oxygen gas

  4. Oxygen released as waste, hydrogen picked up by NADP
• Purpose of light-dependent stage

  To make the two "energy" rich compounds ATP & NADPH
• Light-independent reactions (Calvin Cycle/Carbon Fixation)

  1. Carbon dioxide (CO2) and hydrogen (H2) enters a complex biochemical cycle and gets made into glucose, C6H12O6

  2. Glucose produced is stored as insoluble starch, used in respiration, or used to make other organic chemicals
• Photosynthesis consists of 2 phases: light-dependent and light-independent
• Factors affecting rate of photosynthesis

  • Light intensity
  • Carbon dioxide concentration
  • Temperature
• Light intensity


  The more photons of light that fall on a leaf, the greater the number of chlorophyll molecules that are ionised and the more ATP and NADPH are generated
• Carbon dioxide concentration


  An increase in the carbon dioxide concentration increases the rate at which carbon is incorporated into carbohydrate in the light-independent reaction, and so the rate of photosynthesis generally increases until limited by another factor
• Temperature


  As enzymes in the light-independent reactions approach their optimum temperatures, the overall rate increases. Above the optimum temperature the rate begins to decrease, as enzymes are denatured, until it stops
• The rate of a physiological process will be limited by the factor which is in shortest supply (limiting factor)
• Phases of photosynthesis


  • Light-dependent reactions
  • Light-independent reactions
• Light-dependent reactions


  This stage makes ATP and NADPH, occurs in the thylakoid membranes of the grana inside the chloroplast
• Light-independent reactions (Calvin Cycle/Carbon Fixation)

  This process occurs in the stroma, the liquid matrix of the chloroplast, using ATP and NADPH produced in the light-dependent stage
• The glucose produced in photosynthesis is stored as insoluble starch, used in respiration, or used to make other organic chemicals
• The three main factors that affect the rate of photosynthesis are light intensity, carbon dioxide concentration, and temperature
• Photosynthesis can be measured by the rate of oxygen released or carbon dioxide consumed
• Photosynthesis is a process that involves a series of enzyme-controlled chemical reactions