Limiting Factors | Biology for GCSE/IGCSE - Year 11 PDF Download

Limiting Factors: Extended

• When plants have an abundance of sunlight, carbon dioxide, and water, their rate of photosynthesis is primarily constrained by their capacity to absorb and utilize these resources effectively.
• However, in natural conditions, plants often face limitations in one or more of these essential resources, leading to a constrained rate of photosynthesis determined by the factor that is most scarce.
• A limiting factor refers to an environmental component that is in insufficient supply, thereby impeding vital life processes.
• The rate of photosynthesis can be restricted by three primary factors:
  • Temperature
  • Light intensity
  • Carbon dioxide concentration
• Although water is indispensable for photosynthesis, it is seldom a limiting factor due to the relatively small quantity required compared to the volume of water transpired by a plant, ensuring an ample supply for photosynthetic processes under most circumstances.

Temperature

• Elevated temperatures typically enhance the rate of photosynthesis because enzymatic reactions driving the process become more efficient.
• Nevertheless, this pattern is limited by the susceptibility of enzymes to denaturation at higher temperatures, causing a decline in the rate of reaction beyond a certain threshold.

Light intensity

• Increased light intensity generally correlates with a higher rate of photosynthesis in plants.
• However, this relationship persists only until another limiting factor, such as the availability of carbon dioxide or optimal temperature, constrains further increases in the rate of photosynthesis.

• When light intensity is low, augmenting it initially boosts the rate of photosynthesis. However, there's a threshold beyond which further increases in light intensity no longer enhance the rate. At this point, another factor becomes the limiting factor.
• Factors like insufficient temperature or inadequate carbon dioxide levels might limit the rate when the graph line levels off.

Carbon dioxide concentration

• Carbon dioxide is essential for photosynthesis, serving as one of its raw materials.
• Consequently, higher concentrations of carbon dioxide facilitate a faster reaction rate.
• This pattern persists until the rate plateaus due to the limitation imposed by another factor essential for photosynthesis, which becomes scarce.

• When the line on the graph remains horizontal, it suggests that factors like insufficient temperature or inadequate light could be constraining the rate.