Photosynthesis

• Photosynthesis


  The process by which plants synthesise glucose using light energy from the Sun. Light energy is converted into chemical energy.
• Photosynthesis

  Carbon dioxide + water → glucose + oxygen
• Photosynthesis

  An endothermic reaction - energy is transferred from the environment to chloroplasts by light
• Showing that a plant gives off oxygen during photosynthesis

  Using a water plant (eg. Elodea), collect gas bubbles produced during photosynthesis. The gas will relight a glowing splint as it contains oxygen.
• Leaf adaptations that maximise the rate of photosynthesis


  • Broad leaves - maximise surface area
  • Thin leaves - short diffusion distance
  • Chlorophyll present - trap light energy
  • Veins - transport water to leaves via xylem, remove photosynthesis products via phloem
  • Air spaces - allow CO2 to enter and O2 to leave
  • Guard cells - control opening of stomata for gaseous exchange and prevent water loss
• Factors that affect the rate of photosynthesis


  • Temperature
  • Light intensity
  • Carbon dioxide concentration
  • Amount of chlorophyll
• Increasing temperature

  Increases the rate of photosynthesis as the kinetic energy of particles is increased. The rate decreases past a certain temperature as enzymes become denatured.
• Increasing light intensity

  Increases the rate of photosynthesis until another factor becomes limiting
• Increasing carbon dioxide concentration

  Increases the rate of photosynthesis (until another factor becomes limiting) as CO2 is required to make glucose
• Decreasing the amount of chlorophyll

  Decreases the rate of photosynthesis as chlorophyll is required to absorb light energy
• Limiting factor


  An environmental factor which can restrict the rate of photosynthesis eg. light intensity
• Farmers controlling limiting factors

  They can control temperature, light intensity and CO2 concentration to achieve the fastest possible rate of photosynthesis, leading to a greater yield
• Inverse square law

  Light intensity ∝ 1 / distance^2
• Uses of glucose produced during photosynthesis

  • Respiration
  • Starch for storage
  • Cellulose for strength
  • Amino acid and protein synthesis (combined with nitrates)
  • Lipids for energy storage in seeds