The Rate of Photosynthesis

• Not Enough Light


  • Slows Down the Rate of Photosynthesis
• Light provides the energy needed for photosynthesis


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

  2. Beyond that, it won't make any difference-an light intensity increases, the rate will no longer increase

  3. This is because it'll be either the temperature or the CO, level which is now the limiting factor, not light
• In the lab you can change the light intensity by moving a lamp closer to or further away from your plant
• To get a graph like the one above you either need to measure the light intensity at the plant using a light meter or do a bit of nifty maths with your results
• Too Little Carbon Dioxide

  • Also Slows it Down
• As with light intensity, the amount of CO, will only increase the rate of photosynthesis up to a point


  1. After this the graph flattens out-as the amount of CO, increases, the rate no longer increases

  2. This shows that CO, is no longer the limiting factor
• As long as light and CO, are in plentiful supply then the factor limiting photosynthesile must be temperature
• Temperature has to be Just Right

  • If the temperature is too low, the enzymes needed for photosynthesis work more slowly
  • If the plant gets too hot, the enzymes it needs for photosynthesis and its other reactions will be damaged
• This happens at about 45 °C (which is pretty hot for outdoors, although greenhouses can get that hot if you're not careful)
• You could get a graph that shows more than one leviting factor on the rate of photosynthesis
• Oxygen Production Shows the Rate of Photosynthosis

  1. An of white light is placed at a specific distance from the pondweed

  2. The pondweed is left to photosynthesce for a set amount of time

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

  4. At the end of the experiment, the syringe is used to draw the gas bubble in the tube up alongside a ruler and the length of the gas bubble is measured

  5. This w proportional to the volume of 0, produced
• For this experiment, ang variables that could affect the results should be controlled, eg. the tenperahere and camp
• The experiment is seated twice with the light source at the same diciance and the gean volume of 0, produced is calculated
• Then the whole speed repeated with the light source at different distances from the pondweed
• The feet tube of pondweed can be put into a water bath at a set tengerahan, or dum hydrogencarbonate can be desolved in the water (which gives off co. The poiment can then be peated with different temperatures of water/concentrations of sodium hydrogencarbonate
• Inverse Square Law


  Light intensity decreases in proportion to the square of the distance
• Use the inverse square law to calculate the light intensity when the lamp is 10 cm from the pondweed


  1. The distance is squared

  2. light intensity-- 1/10^2 = 0.01 arbitrary units
• Greenhouses


  • Help to trap the Sun's heat, and make sure that the temperature doesn't become limiting
  • Farmers and gardeners can also increase the level of carbon dioxide in the greenhouse
  • Keeping plants enclosed in a greenhouse also makes it easier to keep them free from pests and diseases
  • Farmers can add fertilisers to the soil as well, to provide all the minerals needed for healthy growth
• Borting all this out costs money-but if the farmer can keep the conditions just right for photosynthesis, the plants will grow much faster and a decent crop can be harvested much more often, which can then Be gold