Photosynthesis

• Photosynthesis

  Uses light energy
• Chlorophyll


  Traps the light in chloroplasts and is the pigment in leaves
• Photosynthesis word equations

  Carbon dioxide + water → glucose + oxygen
• Photosynthesis is an endothermic reaction as it requires light
• How do you destarch a plant


  Lean the plant in darkness for 48 hours
• Destarch the plant to ensure any starch produced is only from the investigations
• Fate of gases in photosynthesis

  Oxygen is initially converted to starch
• Products of photosynthesis


  • Glucose
  • Other sugars
  • Fats and oils
  • Proteins
  • Cellulose
• Starch test


  1. Boil the leaf in water

  2. Boil the leaf in ethanol

  3. Boil the leaf in water again

  4. Spread the leaf on white paper and flood with iodine
• If starch is present, the iodine will turn from yellow-brown to blue-black
• Showing carbon dioxide is needed for photosynthesis


  1. Destarched a plant

  2. Set up with sodium hydroxide to absorb CO2

  3. Leave in bright light for at least 6 hours

  4. Test a leaf for starch
• A negative starch test will show carbon dioxide is necessary for photosynthesis
• Measuring the rate of photosynthesis


  Use apparatus to measure oxygen bubble production
• The rate of oxygen bubble production determines the rate of photosynthesis
• Investigating the need for light and chlorophyll in photosynthesis


  1. Destarched a variegated plant

  2. Cover part of a leaf

  3. Place in bright light for several hours

  4. Test leaf for starch
• Only the areas with chlorophyll will test positive for starch, showing chlorophyll is necessary for photosynthesis
• Only the areas exposed to light will test positive for starch, showing light is necessary for photosynthesis
• Leaf structure


  • Veins carry water and dissolved sugar
  • Palisade layer has tightly packed cells full of chloroplasts
  • Cuticle is waxy and transparent
  • Upper epidermis is transparent
  • Stomata allow gas exchange
  • Spongy mesophyll has air spaces for gas exchange
• Aerobic respiration


  Glucose + oxygen → water + carbon dioxide
• Plants respire 24 hours a day, but photosynthesis only occurs during the day
• At the compensation point, the rates of photosynthesis and respiration are equal, so there is no net exchange of gases
• Adaptations for light absorption


  • Short distance from top to bottom
  • Large surface area
  • Presence of chloroplasts rich in chlorophyll
  • Tightly packed palisade cells
  • Thin, transparent, waterproof cuticle
• Adaptations for gas exchange


  • Large air spaces in spongy mesophyll
  • Gases enter and leave through stomata
• Photosynthesis takes place mainly in the leaves
• The plant produces glucose through photosynthesis and stores it as starch, while the oxygen is released into the air