photosynthesis

• photosynthesis is a metabolic pathway of many different reactions. It is the process of energy transfer from light energy to chemical bond energy.
• stages of photosynthesis

  1. light dependant reactions
  2. light independent reactions
• chloroplasts act as transducers as they convert light energy to chemical energy
• stroma is a gel like fluid that contain enzymes to catalyse reactions in photosynthesis. this means rate of photosynthesis is effected by temperature change as the enzymes can denature at high temperatures.
• 70s ribosomes in chloroplasts make proteins needed for photosynthesis (catalytic enzymes)
• thylakoid membrane is a double membrane with a lumen and contains chlorophylls and accessory pigments/ carotenoids.
• grana are stacks of thylakoid membranes and create maximum surface area for light absorption by having lots of photosystems.
• photosystem 1 absorbs light wavelength 700nm
• photosystem 2 absorbs light wavelength 680nm
• starch granules store glucose
• lamellae are membrane connections between grana stacks which act as transfer tubes for molecules during photosynthesis
• light dependant stage uses water to produce oxygen
• light independent stage reduces carbon dioxide to produce glucose
• light dependant reactions produce NADPH and ATP
• light independent reactions produce ADP, NADP and glucose
• light dependant reactions take place in thylakoids
• light independent reactions take place in the stroma
• despite not needing light the light independent reactions need the products from the light dependant reactions in order to work so needs light in order for the light dependant reactions to take place.
• photosynthetic pigments are coloured biological compounds that is present in chloroplasts and photosynthetic bacteria which absorb light for photosynthesis.
• chlorophylls absorb red and violet blue wavelengths of light and reflects green light
• carotenoids absorbs blue violet wavelength light and reflect red, yellow and orange light
• carotenoids are...

  carotenes and xanthophylls
• a photosystem is clusters of chlorophylls and accessory pigments around a reaction centre that absorb and process light.
• photosystems are found in the thylakoid membrane
• photosystems absorb light via the accessory pigments first. the energy is directed toward chlorophyll A in the reaction centre by vibrating across accessory pigment molecules. the energy then causes photo ionisation of chlorophyll A in the reaction centre
• 2 types of chlorophyll

  1. chlorophyll A (most abundant)
  2. chlorophyll B (less abundant)
• reactants in light independent reaction

  • NADPH
  • CO2
  • ATP
• independent light reaction is Calvin cycle
• rubisco catalyses reaction of CO2 and RuBP in calvin cycle. CO2 + RuBP creates unstable 6 carbon molecule