requirement: light

• practical: why do plants need light for photosynthesis (4)

  1. use a leaf which has grown without any light eg: in cupboard for 48 hours -> here it will use up its starch stores
  2. cut leaf from plant + test it for starch using iodine solution. you will notice it WILL NOT turn blue-black
  3. this indicates that no starch has been produced + so light is needed for photosynthesis
  4. use another plant which has grown with light + compare results (as this one should turn blue-black)
• hint


  1. use plant grown with no light
  2. cut leaf+test for starch
  3. this indicates..
  4. use another plant with light
• how to ensure this is a fair test

  ensure it is warm enough (suitable temp) + there is alot of co2 (so it can photosynthesize)
• how many steps are there

  4
• 1st step

  1. use a plant which has grown with no light eg: in cupboard for 48 hours
• 2nd step


  cut leaf from plant + test for starch using iodine solution. you will notice leaf will not turn blue-black
• 3rd step


  this indicates that no starch has been produced, meaning light is needed for photosynthesis
• 4th step


  use another plant which has grown with light + compare results (as this should have turned blue-black)
• what can this experiment also be used for

  making a leaf destarched
• why is destarching important

  it ensures that any starch present in leaves after experiment was produced during experiment itself rather than left over from before

  • this allows us to test whether a factor eg: light/ co2 is necessary for photosynthesis by confrmng the production of starch afterwards