photosynthesis

• Oxidized


  Loss of electrons
• Reduced


  Gain of electrons
• Redox reactions


  Electron transfer
• Photosynthesis


  • Reduced gains more energy
  • Flow of electrons can do work
• Leaves


  • Palisade layer
  • Spongy layer
• Chloroplast


  • Upper epidermis
  • Lower epidermis
  • Guard cells
  • Stoma
• Electromagnetic radiation (EMR)


  • Shorter wavelength - higher energy
  • Longer wavelength - lower energy
• Absorbing light


  1. Thylakoid membranes

  2. Outer membrane

  3. Inner membrane
• Pigments


  Absorb different wavelengths of light
• Visible light is composed of EMR with wavelength of about 380-750nm
• Blue light has shorter wavelength, red light has longer wavelength
• Light can be absorbed, reflected or transmitted
• Chlorophyll absorbs most strongly at blue (430 nm) and red (662 nm)
• Carotenoids absorb best at orange (662 nm), yellow (590 nm) and green (520 nm).
• Photosystem II is located on the thylakoid membrane.
• Accessory pigments include carotenes and phycobilins.
• Water splits into oxygen and hydrogen ions when exposed to sunlight.
• Pigments in plants


  Absorb specific wavelengths of light (absorption spectrum)
• Action spectrum


  Indicates the wavelength that is most effective
• Chlorophyll


  The main pigment that absorbs light energy, found on the thylakoid membrane of the grana
• Light-dependent reactions


  1. Trap solar energy and use it to generate ATP and NADPH

  2. Occur on the thylakoid membranes
• Light-independent reactions (Calvin cycle)

  1. Use ATP and NADPH to reduce CO2 and produce glucose

  2. Occur in the stroma
• Photosynthetic pigments


  • Compounds that absorb certain wavelengths of visible light, while reflecting others (giving the pigment its specific colour)
  • Photosynthetic pigments trap light energy and pass it on to other chemicals (e.g. chlorophyll)
• Absorption spectrum


  A graph that shows the amounts of light of different colours that a compound absorbs
• Photosynthetic pigments


  • Chlorophyll
  • Carotenoids
  • Accessory pigments
• Photosystems


  • Chlorophyll and other pigments are arranged in clusters called photosystems
  • There are two photosystems: Photosystem I and Photosystem II
• Light-dependent reactions in photosystems


  1. Light energy excites electrons in the reaction centre

  2. Excited electrons are passed through a series of electron carriers

  3. Energy released during electron transport is used to generate ATP and NADPH
• Oxygen is released as a byproduct of the light-dependent reactions
• Calvin cycle (light-independent reactions)


  1. CO2 is reduced using ATP and NADPH to produce glucose

  2. RuBP is joined with CO2 by the enzyme Rubisco

  3. The 6-carbon compound is broken down into two 3-carbon compounds (G3P)

  4. G3P is used to synthesize glucose or regenerate RuBP
• Excited electrons move through an electron transport chain.
• In plants, the Calvin cycle takes place in the stroma of chloroplasts.
• ATP synthase uses the proton gradient created by the electron transport chain to make ATP from ADP and phosphate.
• The Calvin cycle requires ATP and NADPH produced during the light-dependent reactions.
• Light energy absorbed by pigments in thylakoid membranes drives the production of ATP and NADPH.
• photolysis: spliting water molecules into 2 hydrogens and 1/2 oxygen and 2 electrons
• photolysis uses light energy to break down water into hydrogen and oxygen and electrons
• the photosynthesis formula is 6CO2 + 6H2O -> C6H12O6 + 6O2
• the reaction centre is a electron acceptor that accepts electrons from the light energy
• electrons from photosystem 2 leaving the reaction centre go to an electron acceptor to an electron carrying molecules (phytochrome)
• chemiosmosis: the movement of electrons across the thylakoid membrane to create a concentration gradient where it is used to generate ATP in the ATPase