Edexcel IGCSE Biology 复习笔记 2.5.6 Practical: Investigating Chlorophyll & Photosynthesis

Edexcel IGCSE Biology 复习笔记 2.5.6 Practical: Investigating Chlorophyll & Photosynthesis

Practical: Investigating Chlorophyll and Photosynthesis

 

  • Starch is stored in chloroplasts where photosynthesis occurs so testing a leaf for starch is a reliable indicator of which parts of the leaf are photosynthesising
  • This method can also be used to test whether chlorophyll is needed for photosynthesis by using a variegated leaf (one that is partially green and partially white)

 

 

 

Apparatus

  • Beakers
  • Leaf tissue (leaves must be variegated)
  • Bunsen burner
  • Tripod
  • Gauze platform
  • Prongs
  • Ethanol
  • Apron
  • Safety goggles
  • Gloves
  • Iodine solution
  • White tile

 

 

Method

  • Drop the leaf in boiling water
    • This kills the tissue and breaks down the cell walls

     

  • Transfer the leaf into hot ethanol in a boiling tube for 5-10 minutes
    • This removes the chlorophyll so colour changes from iodine can be seen more clearly

     

  • Dip the leaf in boiling water
    • This is done to soften the leaf tissue after being in ethanol

     

  • Spread the leaf out on a white tile and cover it with iodine solution

 

Safety

  • Care must be taken when carrying out this practical as ethanol is extremely flammable, so at that stage of the experiment, the Bunsen burner should be turned off
  • The safest way to heat the ethanol is in an electric water bath rather than using a beaker over a Bunsen burner with an open flame

 

 

 

Results and analysis

  • The white areas of the leaf contain no chlorophyll and when the leaf is tested only the areas that contain chlorophyll stain blue-black
  • The areas that had no chlorophyll remain orange-brown as no photosynthesis is occurring here and so no starch is stored

 

 

Applying CORMS evaluation to practical work

  • When working with practical investigations, remember to consider your CORMS evaluation

 

CORMS-evaluation

 

CORMS evaluation

 

 

 

  • In this investigation, your evaluation should look something like this:
    • C - We are changing whether there is chlorophyll or no chlorophyll
    • O - The leaves will be taken from the same plant or same species, age and size of the plant
    • R - We will repeat the investigation several times to ensure our results are reliable
    • M1 - We will observe the colour change of the leaf when iodine is applied
    • M2 - ...after 1 day
    • S - We will control the temperature of the room and the light intensity

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