topic 01 - photosynthesis

• what forms the basis of any food chain?


  photosynthetic plants and algae
• aside from biomass and energy, what else do photosynthetic plants and algae produce?


  oxygen.
• where do the chemical reactions of photosynthesis occur?


  wherever there are chloroplasts
• where are most of the chloroplasts in plants?


  in the leaves.
• how are leaves perfectly designed to be the centre of photosynthesis?


  • full of chloroplasts
  • large SA so lots of available SA for gases to diffuse in and out of
  • usually thin, minimises diffusion pathway
  • arranged so leaves don't compete for light
  • outer cuticle is transparent, prevents excess water loss but doesnt block light
• which cells catch the light that falls on a leaf?

  the palisade cells
• where in a leaf are most chlorophyll?


  under the palisade cells.
• what does the stomata provide?


  exit and entrance to the outside environemnt
• why is the stomata necessary?


  allows gas exchange to occur right into the cell and allows loss of water vapour
• what is water vapour integral to?


  transpiration pull, that draws water and minerals up through the roots
• what controls the opening of the stomata?


  the guard cells
• what do the guard cells need to offset?


  offset the need for gases with minimising water loss
• what do the xylem and phloem branch off into? where do they terminate?


  branch into veins of the leaf and terminate deep in the leaves.
• what do the veins deliver to and take from?


  the spongey mesophyll layer.
• what are also in the spongey mesophyll layer?


  air spaces
• what is the overall biochemical reaction of photosynthesis?


  6CO2 + 6H2O --> C6H12O6 +6O2
• what is the word equation for photosynthesis?


  carbon dioxide + water --> glucose + oxygen
• what does the overall biochemical equation mean?


  this is what we start with, carbon dioxide and water, and what we wend up with is glucose and oxygen.
• what type of pathway is photosynthesis?

  a metabolic pathway
• is the overall biochemical reaction an oversimplification?


  YES, photosynthesis is a complex series of processes that has many intermediate stages and reactions between reactants to products.
• what are the 3 main parts of the metabolic pathway?


  1. light energy captured by chlorophyll in the chloroplasts.
  2. the light dependent reaction.
  3. the light independent reaction.
• what are the 2 main parts of any chloroplast?


  1. the grand
  2. the stroma
• what is the stroma?


  the fluid that fills the chloroplast, the site of the light independent reactions.
• what is the grana?


  individual stacks of smaller structures called thylakoids. Thylakoids contain the pigments like chlorophyll. The site of light dependent reactions.
• what is the 1st stage of the metabolic pathway?


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


  light energy is captured by the chlorophyll in the thylakoids. Serves 2 purposes.
• what is the 1st purpose of the light dependent reaction?


  the production of ATP, as energy is needed to add an inorganic phosphate to an adenosine diphosphate molecule.
• what is further energy used for in the light dependent reaction?

  photolysis.
• what is photolysis?

  where water molecules are split or ionised into H+ or OH-
• what is the key principle behind light dependent reactions?


  redox reactions
• what is oxidation?


  • loss of electrons
  • addition of oxygen
  • loss of hydrogen
• what is reduction?


  • gain of electrons
  • loss of oxygen
  • addition of hydrogen
• does oxidation reactions release or take in energy?


  releases energy
• do reduction reactions release or take in energy?


  take in energy
• how do light dependent reactions start?


  the uptake of light from the sun within the thylakoids.
• what happens when a molecule of chlorophyll absorbs the light energy?


  a pair of its electrons are promoted to a higher energy level and they are ejected from the molecule.
• what is photoionisation?


  when a molecule of chlorophyll absorbs light energy, a pair of its electrons are promoted to a higher energy level and they are ejected from the molecule. So the chlorophyll molecule becomes a positive ion.
• what occurs to the electrons after they are ejected from the chlorophyll molecule?


  the free electrons are picked up by an electron carrier molecule, the electrons pass along a series of electron carrier molecules in consecutive redox reactions, as they pass the electrons gradually lose energy as each electron carrier is in a lower energy level.
• what happens to the energy lost as electrons are passed along electron carrier molecules?


  the energy is used to add an inorganic phosphate to an ADP molecule to form ATP.
• what is the electron transport chain?


  the series of redox reactions that happen as electron carrier molecule pass along a pair of electrons. The electrons lose energy as this happens and the energy goes towards adding an inorganic phosphate to an ADP molecule to form an ATP molecule.