textbook

• what are chloroplasts?


  flattened organelle surrounded by a double membrane. Found in plant cells.
• what is grana?


  • stacks of thylakoids in the chloroplasts.
  • grant like together by lamellae
• what are thylakoids?


  fluid filled sacs
• what do chloroplasts contain?


  photosynthetic pigments (eg: chlorophyll a)
• what are pigments?


  coloured substances that absorb the light energy needed for photosynthesis.
• where are chlorophyll found?


  in the thylakoid membranes
• what is a photosystem?


  chlorophyll attached to proteins.
• what are the 2 photosystems used in plants to harness light energy?


  • photosystem I
  • photosystem II
• what wavelength does photosystem I absorb?


  700 nm
• what wavelength does photosystem II absorb?


  680 nm
• what is in the inner membrane of the chloroplast and surrounds the thylakoids?

  • stroma
• what is the stroma? what does it contain?


  • jelly like substance
  • contains enzymes, sugars and organic acids
• why are there starch grains in the stroma?


  carbohydrates made through photosynthesis aren't used straight away so are stored as starch grains in the stroma.
• what are the 2 stages of photosynthesis?


  • light dependent reaction
  • light independent reaction
• what happens in the light dependent reaction?


  • light energy absorbed by chlorophyll in the photosystem in the thylakoid membrane.
  • the light energy excites the electrons in the chlorophyll, they are released from the molecule.
  • some of the energy from the released electrons is used to add a phosphate group to ADP to form ATP, and some is used to reduce NADP to form reduced NADP.
  • APT transfers energy and reduced NADP transfers hydrogen to the light independent reaction.
  • during tis, water is oxidised to oxygen.
• describe the process of photoionisation?


  • light energy absorbed by chlorophyll
  • light energy excites a pair of electrons, they move to higher energy level and eventually leave the molecule
• what happens in the light independent reaction?


  • takes place in the stroma of the chlorophyll
  • the ATP and reduced NADP from the light dependent reaction supply the entry and hydrogen to make simple sugars from carbon dioxide.
• in summary, what does the light dependent reaction produce in terms of the photosynthesis equation?


  uses water to form oxygen.
• in summary, what does the light independent reaction produce in terms of the photosynthesis equation?


  uses carbon dioxide to form glucose.
• in the light dependent reaction, what is the energy resulting from chlorophyll being photo ionised used for?


  • making ATP from ADP and inorganic phosphate.
  • making reduced NADP from NADP
  • splitting water into protons electrons and oxygen,
• describe photophosphorylation?


  ATP is made from ADP and an inorganic phosphate using the energy produced through the photoionisation of a chlorophyll molecule.
• describe photolysis?


  splitting water into proteins (H+), electrons and oxygen, using the energy produced through the photoionisation of a chlorophyll molecule.
• what are the 2 types of photophosphorylation?


  • non-cyclic
  • cyclic
• what is the difference in the 2 types of photophoshorylation?


  • they have different products.
• in the thylakoid membrane, what links the photosystems?


  electron carriers.
• what are electron carriers?


  proteins that transfer electrons
• what is the electron transport chain?


  • comprises of photosystems and electron carriers.
  • = a chain of protons through which excited electrons can flow.
• what is stage 1 of non-cyclic photophosphorylation?


  • light energy is absorbed by PS II
  • the light energy excited electrons in the chlorophyll
  • the electrons move to a higher energy level
  • the high energy electrons are released from the chlorophyll and move down the electron transport chain to PS I
• what is important to note about the stages of photophosphorylation?


  they are all happening at the same time, they are split into stages to make it easier to remember.
• what is stage 2 of non-cyclic photophosphorylation?


  • as the excited electrons from the chlorophyll leave PS II to move down the electron transport chain, they must be replaced
  • light energy splits water into protons (H+), electrons and oxygen. This is photolysis.
  • reaction : H2O --> 2H+ + 0.5 O2
• what is stage 3 of non-cyclic photophosphorylation?


  • the excited electrons lose energy as they move down the electron transport chain
  • the enrage is used to transport protons into the thylakoid, so the thylakoid has a higher conc of protons than the stroma. This makes a proton gradient across the thylakoid membrane.
  • protons move down the conc gradient into the stroma via ATP synthase (enzyme), this is embedded in the thylakoid membrane
  • the energy from this movement combines ADP and inorganic phosphate to form ATP.
• what is stage 4 of non-cyclic photophosphorylation?


  • light energy is absorbed by PS I which excites the electrons again to an even higher energy level.
  • finally, the electrons are transferred to NADP, along with a proton (H+) from the stroma to form reduced NADP.
• what is chemiosmosis?


  the process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis.
• what is cyclic photophosphorylation?


  • only uses PS I
  • cyclic because the electrons from the chlorophyll molecule aren't passed onto NADP but are passed back to PS I via electron carriers.
  • so the electrons are recycled and can repeatedly flow through PS I
  • this doesn't make any reduced NADP or oxygen.
  • it only produces small amounts of ATP.