Question

State Blackman’s law of limiting factors.

Answer 1

Various factors affect the process of photosynthesis. Scientists study the effect of individual factors that affect the rate of photosynthesis. Blackman’s law explained how the rapidity of increase by a number of factors. Slowest factors affect the rate of reactions. Carbon dioxide and light intensity are the limiting factors of photosynthesis. Blackman explains it graphically. Intensity of light affects the process. Rate of photosynthesis increases by the increase in concentration of carbon dioxide

Complete answer:
F.F. Blackman in 1905 illustrates the law of limiting factors. Light intensity affects the absorption of carbon dioxide by the leaves. A leaf utilizes 5 mg. of carbon dioxide in one hour if exposed to a certain light intensity. In case only 1 mg. of carbon dioxide enters the leaf in an hour, it shows that the rate of photosynthesis is limited due to the carbon dioxide factor. Increase in the concentration of carbon dioxide increases the rate of photosynthesis. When 5 mg of carbon dioxide is absorbed by leaf then any further absorption of carbon dioxide will not affect the rate of photosynthesis. It becomes constant. This phenomenon is observed when low light intensity is present. So it can say that low light intensity is the limiting factor. If the intensity of the light increases from low to medium, then increase in carbon dioxide concentration and rate of photosynthesis is observed. This continues further and when there is presence of high light intensity rate of photosynthesis increases.

From the above information we came to know that the rate of photosynthesis cannot be increased by increasing only one factor. Increases of other factors should be in the proper proportion to get a favorable effect. Besides light and carbon dioxide there are some other factors which affect the rate of photosynthesis are temperature, water etc. these can also become limiting factors under certain conditions.

Note: Blackman’s law of limiting factors can be applicable to any physiological process in which more than one factors are involved. Factors present in small amounts act as limiting factors due to its requirement in higher amounts. Other scientists oppose this law, they explain that the rate of photosynthesis declines gradually whenever a factor has become limiting. Location of chloroplast can also affect the absorption of light which can ultimately become a limiting factor for the rate of photosynthesis.