Question

What is the law of limiting factors? Explain it with an illustration.

Answer 1

Hint: This law is also known as Blackman’s law of limiting factor as it was given by Blackman in 1905. This law states that when a process is carried out by depending on a number of factors or many of the factors the rate of the process depends only on the factor that is present in small quantity means that is limited.

Complete answer:
This law is applicable when we see the process of photosynthesis. The rate of photosynthesis is very important in determining the yield of the plants including crop plants, An understanding of the factors that affects photosynthesis is very necessary. Photosynthesis is under the influence of both external and internal (plant) factors.
In 1905, Blackman gave the Law of Limiting factors. When several factors affect any biochemical process, then this law comes into effect. This states that:
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.
To illustrate the law, suppose light intensity supplied to a leaf is just sufficient to utilize 5 mg of $\mathop {CO}\nolimits_2 $, per hour in photosynthesis. As the $\mathop {CO}\nolimits_2 $ supply is increased, the rate also increases till 5 mg of $\mathop {CO}\nolimits_2 $enters the leaf per hour. After that, any further increase in the supply of $\mathop {CO}\nolimits_2 $ does not have any effect on the rate. Light has now become the limiting factor and further increase in rate of photosynthesis will occur only by increasing the intensity of light.

Note: Carbon dioxide concentration is the major limiting factor influencing the rate of photosynthesis. The concentration of $\mathop {CO}\nolimits_2 $is very low in the environment (between 0.3 percent to 0.04 percent). This level of carbon dioxide is far below the requirement for optimum photosynthesis.