Factors affecting Photosynthesis

An understanding of the factors that affect photosynthesis is necessary, because the rate of photosynthesis is very important in determining the yield of plants, including crop plants. Photosynthesis is under the influence of several factors, both internal (plant) and external.

• Plant (internal) factors include the number, size, age and orientation of leaves, the mesophyll cells and chloroplasts, the internal CO2 concentration, and the amount of chlorophyll. These internal factors are dependent on the genetic predisposition and the growth of the plant.
• External factors include the availability of sunlight, temperature, CO2 concentration and water.

As a plant photosynthesises, all these factors will affect its rate simultaneously. However, usually one factor is the major cause, or is the one that limits the rate. Hence, at any given point the rate will be determined by the factor available at sub-optimal levels.

When several factors affect any biochemical process, Blackman's (1905) Law of Limiting Factors comes into effect. It states:

• If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value: it is the factor which directly affects the process if its quantity is changed. …