PHOTOSYNTHESIS by kk4RGwmf

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									PHOTOSYNTHESIS
           Photosynthesis
• The process by which plants make their
  own food
• Simple substances, carbon dioxide and
  water are used as raw materials
• Light energy is needed for the process to
  occur
 Photosynthesis word equation


                           light energy

• Carbon dioxide + water             glucose + oxygen
Where does photosynthesis take
           place?
 Where does photosynthesis take
            place?
• In the chloroplasts in leaf cells
              Chloroplasts
• Most are found in the top layer of cells in
  the leaf where the intensity of light is
  greatest
• They contain the green pigment
  chlorophyll which absorbs the light
  energy needed for photosynthesis
    What happens to glucose?
• It is used immediately for respiration
• It is converted to starch for storage
• It is converted into protein needed for
  growth. This conversion needs nitrates
  which are taken up by the plant in solution
  by its root hair cells.
• It is converted into cellulose for making
  cell walls
   Factors which affect the rate of
          photosynthesis.
• Carbon dioxide levels
• Light intensity
• Temperature- the higher the temperature
  (up to approximately 40ºc) the faster the
  rate
 How can we measure the rate of
       photosynthesis?
• Measure the rate at which oxygen is given
  off.
  How can we demonstrate that a
      plant has carried out
        photosynthesis?


• By testing the leaf for starch. Some of
  the glucose made during photosynthesis is
  converted to starch for storage.
           De-starching plants.

• Plants have to be de-starched before they can
  be used in experiments designed to show which
  factors are needed for photosynthesis.
• This is achieved by placing the plant in the dark
  for 36 hours.
• During this time the starch will be broken down
  and used for respiration.
• Any starch which is subsequently found can only
  have been made during the experiment.
     Testing leaves for starch
• Soften and kill the leaf by dropping in
  boiling water for 30 secs approx
• Place the leaf in boiling ethanol for a few
  minutes to decolourise the leaf
     Testing leaves for starch
• Remove leaf and then place in hot water
  for a few seconds to soften it
• Then carefully spread leaf on a petri-dish
  or white tile and add iodine solution.
  To show that light is needed for
         photosynthesis.
• http://www.biotopics.co.uk/plants/psfac2.ht
  ml

								
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