Photosynthesis (paper 2 notes)

• Structural adaptations of the chloroplast

  • External membrane
  • Internal membrane
  • Starch grain
  • Stroma
  • Lamelle
  • Granum
  • Thylakoid
  • Lamella
  • Quantosome
  • Chlorophyll
• The chloroplast is the small organelle responsible for photosynthesis
• Chloroplast

  • Surrounded by a double membrane
  • Consists of a lameller system/thylakoid
• Thylakoids

  • Consist of stacks, called grana (one-granum)
  • Chlorophyll is found in the grana
  • The light reaction of photosynthesis occurs in the grana
• Stroma


  The fluid surrounding the grana
• Dark reaction of photosynthesis

  Occurs in the stroma
• Starch grains


  Found in the chloroplast
• Importance of photosynthesis


  • Light energy of the sun is converted into chemical potential energy and stored as glucose/starch
  • Carbon dioxide is absorbed during photosynthesis, ensuring a balance in nature and regulating CO2 concentration
  • Photosynthesis is the only method by which carbohydrates (organic nutrients) are synthesized from inorganic substances (CO2 and water), which all animals depend on to live
  • Oxygen is released into the atmosphere, needed for cell respiration in animals and humans
  • Oil and coal are products of photosynthesis, a source of energy for industries
• What happens during photosynthesis

  1. Carbon dioxide diffuses in at the stomata, through the intercellular air pockets, into the chloroplast inside the mesophyll cells

  2. Water is brought into the mesophyll cells from the xylem in the roots

  3. Light energy of the sun is absorbed by the chlorophyll in the chloroplast and converted to chemical potential energy

  4. Glucose is manufactured from water, carbon dioxide and light energy

  5. Oxygen is released by the cells and diffuses out through the stomata
• EXPERIMENT 1
• THE STARCH TEST: TO TEST FOR STARCH IN THE LEAF
• TO PROVE THAT LEAVES WHICH PHOTOSYNTHESIZED, CONTAIN STARCH
• THE STARCH TEST

  1. Boil the leaf in a glass beaker with water

  2. Place leaf in test tube with alcohol/ethanol

  3. Immerse test-tube in banker with boiling water

  4. Boil leaf in the ethanol

  5. Boil leaf in water again

  6. Spread out the leaf in a petri-dish

  7. Cover with iodine for a few minutos
• Precautionary measures

  • Heat alcohol over water for safety-alcohol is inflammable
  • Break cell walls with boiling water to easily remove chlorophyll from the leaf
  • Chlorophyll is removed by alcohol so that the starch test is visible with iodine
• EXPERIMENT 2
• Before starch test

  1. Take a leaf from a plan which has variegated leaves, such as a geranium, after it has been in the sun for 2-3 hours

  2. Test the leaf for starch-EXPLAIN THE STARCH TEST
• EXPERIMENT 3
• Before the starch test

  1. Place a plant for 24-72 hours in a dark container

  2. Cover part of the leaf of the plant (above and below) with aluminium foil, so that light can not penetrate to the leaf-CONTROL

  3. Open parts without foil-EXPERIMENT

  4. Put plant in the sun for a few hours to photosynthesize

  5. Remove the experimental leaf-test for starch with starch test