Photosynthesis

• Photosynthesis is a endothermic reaction in which energy from sunlight is transferred to the chloroplasts in green plants
• The Products of photosynthesis are:

  • produce starch for storage
  • synthesise lipids or energy source in seeds
  • to form cellulose to make cell walls
  • produce amino acids
• Photosynthesis produces amino acids and when combined with nitrates from the soil, produces proteins
• word equation for photosynthesis:

  carbon + water -- light energy + chlorophyll --> glucose + oxygen
• Carbon dioxide diffuses into the leaf through the stomata
• Glucose is used to make substances needed by the plants. also used in respiration to release energy
• water is taken up the roots and transported by the (hint - x) xylem through the leaves
• 6CO2 + 6H2O --> C6H12O6 + 6O2
• The 3 main factors that affect photosynthesis are:

  • temperature
  • light intensity
  • carbon dioxide concentration
• A limiting factor is something present in the environment in such short supply that it restricts life processes
• Temperature factor information:

  • Less temperature means less kinetic energy, resulting in fewer successful collisions over time
  • More temperature means more successful collisions
  • too high temperature will mean the enzyme will denature, which would reduce rate of reaction and photosynthesis
• Light intensity:

  • more light will mean a faster rate of photosynthesis
• When testing a leaf for starch, how do you heat the ethanol safely?

  in a water bath - no lit Bunsen's as ethanol is too flammable
• when testing a leaf for starch, how do you check if starch is present?

  add iodine solution - turns blue/black if starch is present and stays orange if starch is absent
• When testing for starch, Why do you put the leaf in hot ethanol?


  to dissolve chlorophyll
• Magnesium ions are used to make chlorophyll
• Photosynthesis is where light energy is absorbed by chloroplasts and gets turned into chemical energy
• The purpose of photosynthesis is to make glucose, which is used to make other biological ​molecules for growth
• A lack of magnesium ions and nitrate ions will result in a stunted growth and yellowing leaves
• Testing a leaf for starch:

  1. Put the leaf in boiling water

  • this kills the tissue and breaks down the cell wall, which allows the Iodine to penetrate the cells easier
  • 2. Put the leaf in hot ethanol in a boiling tube in a water baths for 5-10 minutes
  • this removes chlorophyll, so the colour change is clearer
  • 3. rinse the leaf in cold water
  • this softens the leaf tissue after it's in ethanol
  • 4. spread out the leaf on a white tile and cover it with iodine solution
• Practical of rate of photosynthesis:

  1. take a bundle of your organism (e.g. pondweed)
  2. submerge them in a beaker of water underneath an upturned funnel
  3. fill a boiling tube with water and place it over the top of the funnel
  4. when oxygen is produced, the bubble of gas will collect in the boiling tube and displace the water
• when measuring the rate of photosynthesis, how do you prove that oxygen is forming?


  relight a glowing splint
• the quantity of bubbles and volume of oxygen can be changed

  and measured to find out the rate of photosynthesis
• What parts if the leaf will turn blue/black and why?

  areas containing chlorophyll will turn blue/black as starch is present,