Photosynthesis

• Photosynthesis uses light energy to change carbon dioxide and water into glucose and oxygen
• Photosynthesis takes place in chloroplasts and is endothermic as energy is transferred from the environment
• $6CO^2+$$6H^2O$ are the reactants and $C^6H^1$$^2 O^6+$$6O^2$are the products
• Glucose produced in respiration is used in many ways

  • respiration
  • making cellulose for making strong cell walls
  • making amino acids
  • stored as lipids (oils and fats)
  • stored as starch
• Rate of photosynthesis is affected by light intensity, temperature, carbon dioxide concentration, and chlorophyll concentration
• Rate of Photosynthesis


  The rate at which photosynthesis occurs
• Factors affecting the rate of photosynthesis

  • Light
  • CO2
  • Temperature
• ROP - light

  1. Light provides the energy needed for photosynthesis

  2. As the light level is raised, the rate of photosynthesis increases steadily, but only up to a certain point

  3. Beyond that, it doesn't make any difference - as light intensity increases, the rate will no longer increase

  4. This is because it'll be either the temperature or the CO2 level which is now the limiting factor, not light
• Too Little Carbon Dioxide Also Slows it Down

  1. CO2 is one of the raw materials needed for photosynthesis

  2. As with light intensity, the amount of CO2 will only increase the rate of photosynthesis up to a point. After this the graph flattens out

  3. As the amount of CO2 increases, the rate no longer increases. This shows that CO2 is no longer the limiting factor

  4. As long as light and CO2 are in plentiful supply, then the factor limiting photosynthesis must be temperature
• The Temperature has to be Just Right

  1. Usually, if the temperature is the limiting factor it's because it's too low - the enzymes needed for photosynthesis work more slowly at low temperatures

  2. But if the plant gets too hot, the enzymes it needs for photosynthesis and its other reactions will be damaged

  3. This happens at about 45 °C (which is pretty hot for outdoors, although greenhouses can get that hot if you're not careful)
• Oxygen Production Shows the Rate of Photosynthesis

  1. Pondweed can be used to measure the effect of light intensity on the rate of photosynthesis

  2. The rate at which the pondweed produces oxygen corresponds to the rate at which it's photosynthesising

  3. A source of white light is placed at a specific distance from the pondweed

  4. The pondweed is left to photosynthesise for a set amount of time

  5. As it photosynthesises, the oxygen released will collect in the capillary tube

  6. At the end of the experiment, the length of the gas bubble is measured, which is proportional to the volume of O2 produced
• Artificially Creating Ideal Conditions for Farming


  • Greenhouses help to trap the Sun's heat and make sure the temperature doesn't become limiting
  • Farmers can use heaters, shades, and ventilation to control the temperature
  • Farmers can supply artificial light after the Sun goes down to give plants more photosynthesis time
  • Farmers can increase the level of carbon dioxide in the greenhouse, e.g. by using a paraffin heater
  • Keeping plants enclosed in a greenhouse makes it easier to keep them free from pests and diseases
  • Farmers can add fertilisers to the soil to provide all the minerals needed for healthy growth
• Sodium hydrogencarbonate gives off carbon dioxide