01 January 2013

#42 Effect of Temperature on the Rate of Photosynthesis

When the temperature rises the rate of photosynthesis rises also. There is an optimum temperature  at which the rate of photosynthesis is maximum. Beyond this temperature, the reaction quickly comes to a halt.


  • Place a pond weed Elodea upside in a test tube containing water at 25°C.
  • Place the tube in a beaker of fresh water.
  • Place excess sodium bicarbonate (NaHCO3) in the water to give a constant saturated solution of CO2.
  • Place the lamp (the only light source) at a fixed distance from the plant.
  •  Maintain the room temperature at 20°C.

  • Count the number of oxygen bubbles given off by the plant in a one -minute period. This is the rate of photosynthesis at that particular temperature.
  • The gas should be checked to prove that it is indeed oxygen - relights a glowing splint.
  • Repeat at different temperatures: 0°C - surround the beaker with an ice jacket; greater than room temperature (25°C, 30°C, 35°C, 40°C, 45°C, etc.,) by using a hot plate.
  • Graph the results placing temperature on the x-axis.
  • At low temperature, the enzyme does not have enough energy to meet many substrate molecules, so the reaction is slowed. 
  • When the temperature rises, the particles in the reaction move quicker and collide more, so the rate of photosynthesis rises also. 
  • At the optimum temperature, the enzyme is most efficient and the rate if maximum. 

  • At temperatures above 40°C the rate slows down. This is because the enzymes involved in the chemical reactions of photosynthesis are temperature sensitive and destroyed (denatured) at higher temperatures.

Additional sources :   skoool.ie

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