Limiting factors - class-XI

The main factors affecting rate of photosynthesis are light intensity, carbon dioxide concentration and temperature. In any given situation any one of these may become a limiting factor, in other words, the factors that directly affects the rate at which photosynthesis can take place masking the effects of the other factors. A limiting factor in a system is an input or variable such that a small change in it from the present value would cause a non-negligible change in an output or other measure of the system.  

Blackman's Law of limiting factors are the various factors which affect the rate of photosynthesis. It is considered that when the other factors are constant, the factor which is least or minimum has the direct effect on the rate of photosynthesis. Sachs developed three cardinal points for each factor which affects the rate of photosynthesis. These cardinals have minimum, optimum and maximum values. The process of photosynthesis starts at the minimum and takes place at the optimum value. the rate of photosynthesis is much smaller at the maximum value and stops above this point.

Blackman's Law of limiting factors was the elaborated form of the law of minimum given by Liebig. These are the various factors which affect the rate of photosynthesis. It is considered that when the other factors are constant, the factor which is least or minimum has the direct effect on the rate of photosynthesis. 

Enzymes are biological catalysts which can normally function at body temperatures. There are various different enzymes involved in the process of photosynthesis. The enzymes have optimum temperature range. This is the range in which they show maximum activity. The enzymes are proteins which gets denatured at higher temperature. The structure of these enzymes gets modified and the active sites are destroyed. This results in the inactivation of the enzymes. 

In the twentieth century, Blackman (1905) proposed his principle of limiting factors. According to this principle, the rate of photosynthesis controlled by several factors is only as rapid as the slowest factor permits. He claimed that, if all other factors are kept constant the factor under consideration will affect the rate of photosynthesis, starting at a minimum below which no photosynthesis takes place and ending with an optimum at which a horizontal would be established, that is, the rate would remain constant despite further increases in that factor. At this point some other factor becomes limiting.

So, the correct option is 'Photosynthesis'.

Carbon dioxide is a major limiting factor influencing the rate of photosynthesis. The concentration of $CO _{2}$ is very low in the atmosphere (between 0.03 percent and 0.04 percent). This level of carbon dioxide is far below the requirement for optimum photosynthesis. Increase in concentration up to 0.05 percent can cause an increase in the rate of photosynthesis but beyond this level, it becomes damaging over longer periods.

The concept of limiting factors is based on Liebig's Law of the Minimum, which states that growth is controlled not by the total amount of resources available, but by the scarcest resource. For example, space is a limiting factor.

Photosynthesis is the process in which sunlight is used to form carbohydrate mainly glucose by reduction of carbon dioxide and oxidation of water.

The process of carbon assimilation occurs in light independent way. It is called as a dark reaction. Since, Blackman demonstrated the existence of dark reaction, the reaction is also called as Blackman’s reaction.

Blackman proposed the law of limiting factors in 1905. According to this law, when a process depends on a number of factors, its rate is limited by the pace of the slowest factor. Blackman's law of limiting factors determines the rate of photosynthesis. Emerson found that maximum $CO _2$ fixation could be achieved with brief flashes of light. From both observations we can say that only one factor can be limiting in photosynthesis at a time. 

In the year 1905, Blackman proposed the law of limiting factors for photosynthesis. According to this law the process totally depends upon the light factors and its rate is limited by the pace of the slowest factor. This law of limiting factor determines the rate of the photosynthesis.

Law of Limiting factor was given by Blackman This law governs the rate of photosynthesis According to this law, the process of photosynthesis is controlled by many factors but the rate of photosynthesis will depend on the factor which is present in limited quantity.

Blackman's (1905) law of limiting factors 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.