Law of Limiting Factors
வரம்புறு காரணிகளின் விதி
Do not mistake abundance for efficiency. A plant may have infinite light and CO2, but if the temperature is suboptimal, the entire photosynthetic machinery stalls. This is the bottleneck principle. Ignore it, and you lose marks.
The idea
Blackman's Law of Limiting Factors (1905) states that if a chemical process is affected by more than one factor, its rate is determined by the factor nearest to its minimal value. Any change in the quantity of this limiting factor directly changes the rate of the process. Factors like light, CO2 concentration, and temperature act as limiting factors depending on which one is in shortest supply relative to the others.
Why it matters
It explains how multiple environmental variables interact to control the overall rate of photosynthesis.
NEET lens
NEET focuses on the graph interpretation of this law. Memorize that the rate increases until the limiting factor becomes sufficient, then plateaus. Do not confuse 'limiting factor' with 'inhibitor'. Expect questions on which factor is limiting under specific experimental conditions.
Clinical significance
In humans, this is analogous to metabolic rate-limiting enzymes in pathways like Glycolysis. If a single enzyme like Phosphofructokinase is inhibited, the entire ATP production chain collapses. Homeostasis fails when a single critical component falls below the threshold.
Introduction
Blackman's Law of Limiting Factors (1905) states that the rate of a process is limited by the factor that is present in the minimum amount — even if all other factors are optimal.
Core concept
Factors affecting photosynthesis rate: (1) Light intensity — increases rate up to light saturation point. (2) CO₂ concentration — most limiting factor under normal conditions (0.03% atmospheric). (3) Temperature — affects enzyme activity (Calvin cycle enzymes). (4) Water — affects stomatal opening and turgidity. At any given moment, the factor furthest below its optimum is the limiting factor. Increasing any other factor won't increase the rate.
Go deeper
CO₂ concentration is usually the most limiting factor in normal conditions because: atmospheric CO₂ is only 0.04% (400 ppm), far below the saturation point. Greenhouses artificially increase CO₂ to 0.1% → significant increase in crop yield. This demonstrates CO₂ as the primary limiting factor.
From Class 10
When you study, both sleep and food affect your performance. The one you have least of limits you most. The same idea applies to photosynthesis.