Plants Additional - How Plants Produce Food - Photosynthesis

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  • Photosynthesis
    How leaves work to make food

Carbon Dioxide + Water (+ light energy) --> glucose + oxygen
6CO2 + 6H2O ==> C6H12O6 + 6O2

  • Light energy absorbed by chlorophyll.
              - Chlorophyll is stored in little packets called chloroplasts (
  • Light is absorbed by the chlorophyll.
  • The light energy used to convert C02 and water into a simple sugar - glucose
  • The reaction itself actually releases oxygen too
  • Some of the glucose made is used up immediately by the cells of a plant
  •  The rest goes into storage
    • Instead of storing it as glucose it stores it as starch!
    • (DO ze Iodine test) 
      •  yellow-brown liquid which turns blue when it reacts with starch

How leaves are adapted

  • Big, broad leaves with large surface area
    •   Perfect for allowing even more light to fall on them
  • Contain chlorophyll in chloroplasts
    •  These do the absorbing of light
  • Air spaces
    •  Allow C02 to get to the cells and let waste oxygen out
  • Veins
    • Carry water to the leaf cells

Cross Section (

  • Waxy Cuticle
    •  Waterproof layer. Stops water loss.
  • Palisade cells (top of leaf)
    • These cells are at the top of the leaf and very close to the light. They are packed full of chloroplasts to ensure MAXIMUM PHOTOSYNTHESIS
  • Air spaces
    • Gas exchange and storage
    • Large surface area
    • Cells not tightly packed
    • Some chloroplasts
  • Guard cells (bottom of leaf)
    • Open and close stomata
      • Stoma (pl. stomata) allow gases to move in and out of leaf and also prevent water loss when closed.

 What are the limiting factors?

Plants grow quickly in summer and slowly in winter - why?
When the the things they need for photosynthesis are in short supply then these things are known are limiting factors

  • Light
    • Plenty of light = lots of photosynthesis
    • Little light = little photosynthesis
    • Brighter light = faster rate of photosynthesisLight Intensity Graph (


  • Temperature
    • Temperature affects all chemical reactions, ever. This includes photosynthesis too because photosynthesis is basically a chemical reaction


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