Conditions Needed for Photosynthesis (WJEC GCSE Biology)

• The rate at which photosynthesis occurs is affected by several factors in the environment:
  • Temperature
  • Carbon dioxide
  • Light intensity
• Optimal levels of these environmental factors allow photosynthesis to occur at its maximum rate, but any factor that is less-than-optimum can limit the rate of photosynthesis

Temperature

• As the temperature of the environment increases, the rate of photosynthesis also increases
  • At low temperatures the kinetic energy of the molecules inside plant cells is limited, so there are few successful collisions between the photosynthesis reactants per unit of time
  • Increasing temperature increases the kinetic energy of the molecules, increasing the likelihood of successful collisions, and so allowing the reaction to occur faster
• At very high temperatures the enzymes that catalyse photosynthesis can denature, meaning that the complementary shape of the active sites is lost; this causes a steep decline in the rate of photosynthesis

Temperature & photosynthesis graph

As temperature increases, so too does the rate of photosynthesis; this continues until the temperature becomes too high and plant enzymes begin to denature

Light

• The higher the light intensity, the faster the rate of photosynthesis
  • This is because chlorophyll is able to absorb more light energy to power the reactions of photosynthesis
• This trend will continue until another factor prevents the rate from increasing further; such a factor could be:
  • Temperature
  • Carbon dioxide concentration

Light intensity & photosynthesis graph

As light intensity increases, so does the rate of photosynthesis; this continues until another factor prevents the reaction from occurring any faster

Carbon dioxide

• As carbon dioxide concentration increases, so too does the rate of photosynthesis
  • Carbon dioxide is one of the raw materials required for photosynthesis
• This trend will continue until another factor prevents the rate from increasing further; such a factor could be:
  • Temperature
  • Light intensity

Carbon dioxide concentration & photosynthesis graph

As carbon dioxide concentration increases, so does the rate of photosynthesis; this continues until another factor prevents the reaction from occurring any faster

Higher Tier Only

• A perfect set of environmental conditions is very rare, meaning that the rate of photosynthesis is usually limited by factors in the environment
  • These factors are known as limiting factors
• A limiting factor can be defined as:

An environmental factor that limits the rate of reaction when it is in short supply

• The limiting factors for photosynthesis are:
  • Temperature
  • Light intensity
  • Carbon dioxide concentration
• Note that although water is necessary for photosynthesis, it is not considered a limiting factor
  • If water availability is low enough to limit the rate of photosynthesis then the plant is likely to have closed its stomata, slowing photosynthesis due to carbon dioxide intake