Photosynthesis

• Photosynthesis


  The reaction that plants use to trap light energy
• Plants use light for their source of energy
• Photosynthesis


  • It is an endothermic reaction
  • It takes place in the leaves of a plant
  • Leaves contain the green chemical chlorophyll
• Photosynthesis


  1. Plant takes in carbon dioxide and water

  2. Light energy is absorbed by chlorophyll

  3. Light energy is used to convert carbon dioxide and water into glucose

  4. Oxygen is also produced
• Chemical formulas


  • Carbon dioxide (CO2)
  • Water (H2O)
  • Glucose (C6H12O6)
  • Oxygen (O2)
• Light intensity increases


  Rate of photosynthesis increases
• Light intensity is a limiting factor


  Photosynthesis is not as fast as it could be because there isn't enough light
• Carbon dioxide level increases

  Rate of photosynthesis increases
• Carbon dioxide is a limiting factor


  Photosynthesis is not as fast as it could be because there isn't enough carbon dioxide
• Factors affecting rate of photosynthesis

  • Amount of chlorophyll in the leaf
  • Temperature
• Temperature increases


  Enzymes involved in photosynthesis work faster, increasing the rate
• Temperature keeps increasing


  Enzymes denature, decreasing the rate of photosynthesis
• Photosynthesis


  Carbon dioxide + water + light energy → Glucose + Oxygen
• Respiration


  Process that releases energy from glucose in the mitochondria
• Photosynthesis only produces glucose during the day


  Plant cells respire all the time, including at night
• Starch


  Insoluble storage molecule made from glucose, which can be converted back to glucose when needed
• Fats and oils


  Storage form of energy made from glucose in many plants
• Cellulose


  Molecule in the plant cell wall, made from glucose, that gives it strength
• Amino acids


  Made from glucose, used by plants to synthesize proteins
• Plants need to absorb nitrate ions from the soil to make amino acids from glucose
• Investigating the effect of light intensity on the rate of photosynthesis

  1. Take a boiling tube and place it 10 cm away from an LED light source

  2. Fill the boiling tube with sodium hydrogen carbonate solution

  3. Put a piece of pond weed into the boiling tube

  4. Leave for 5 minutes to acclimatize

  5. Start a stopwatch and count the number of bubbles produced in 1 minute

  6. Repeat the experiment at 20 cm, 30 cm, and 40 cm from the light source
• Problems with the practical

  • Number of bubbles can be too fast to count accurately
  • Bubbles are not always the same size
• Solving the problems


  1. Measure the volume of oxygen produced instead of counting bubbles

  2. Use a measuring cylinder to catch the bubbles and measure the volume of oxygen
• Doubling the distance from the light source

  The number of bubbles per minute falls by a factor of 4
• Inverse square law


  If the distance is doubled, the light intensity falls by a factor of 4, which causes the number of oxygen bubbles to fall by 4 times
• Higher tier students need to understand the inverse square law
• Foundation tier students can stop watching now