Factors Affecting the Rate of Photosynthesis (Cambridge (CIE) O Level Biology): Revision Note

Factors Affecting the Rate of Photosynthesis

• The rate of photosynthesis is affected by the availability of its raw materials, and by the energy required for chemical reactions to occur

• The following factors therefore affect the rate of photosynthesis:

  • Light intensity

  • Carbon dioxide concentration

  • Temperature

• Note that while water is a raw material in photosynthesis, it is involved in multiple plant processes, so its effects on photosynthesis are complex and are not covered here

Light intensity

• As light intensity increases, the rate of photosynthesis will also increase

• This is because photosynthesis is a chemical reaction that requires light energy, so when less light energy is available, the reaction occurs at a reduced rate

Carbon dioxide concentration

• As carbon dioxide concentration increases, so does the rate of photosynthesis

• This is because carbon dioxide is a reactant in photosynthesis, so reducing its availability will reduce the rate at which the reaction can proceed

Temperature

• The temperature at which photosynthesis occurs is important because photosynthesis, like many chemical reactions inside living cells, is controlled by enzymes, and temperature affects the rate of enzyme-controlled reactions

• As temperature increases, the rate of photosynthesis increases, up to a point

  • More energy is available for the movement and collision of molecules at higher temperatures

  • It can be said that molecules have more kinetic energy at high temperatures

• At high temperatures, the rate of photosynthesis decreases, and may reach zero

  • At extreme temperatures the specific shape that is essential to enzyme function is lost as chemical bonds inside the enzyme break; this is denaturation, and causes reaction rate to decrease and eventually stop altogether