What is the Law of Limiting Factor definition and examples
A limiting factor is a factor that limits the growth of a population’s size. It denotes the scarcity of essentials necessary for survival and growth. It could be non-availability of biotic factors like resources, food, mates, or abiotic factors like environmental imbalance, extreme weather conditions that stop or limit the growth of organisms in an ecosystem. Limiting factors are generally expressed as a lack of a particular resource that is essential for survival. It ultimately determines a habitat's carrying capacity, which is the maximum size of the population it can support.
Blackman’s Law of Limiting Factors
The law of limiting factors was postulated by a plant physiologist- F.F Blackman. Blackman’s Law in simple language states that a process that is dependent on several factors, the pace of the slowest factor decides the rate of that process.
Blackman postulated this law based on his study on limiting factors on the photosynthesis system of plants.
He stated that the biological factors are affected by several factors, but the rate at which they affect the whole process is different.
Blackman took reference of photosynthesis to prove this. As we know, plants require adequate amounts of water, sunlight, temperature, carbon dioxide, and chlorophyll to carry out photosynthesis. The scarcity of any of these components affects the rate of photosynthesis.
He also illustrated that the rate of photosynthesis cannot be increased by increasing only one factor or altering only one essential component.
Thus, other factors or components should also be increased in proper proportion to achieve a higher rate of photosynthesis.
Therefore, Blackman’s law is based on a principle that the absolute magnitude of factors is less important over their relative magnitudes.
This gives us a theory that any physiological process which is affected by more than one factor is governed by the law of limiting factor.
It should be noted that the factor which is present in higher amounts may be a limiting factor in comparison to the one present in smaller amounts. This is due to more requirements of the factor present in higher amounts.
Thus, when the rate of the process becomes constant due to a limiting factor, it is regulated by regulating the amount of only the limiting factor. For example- a leaf that utilizes 5 mg of CO2 per hour in photosynthesis is exposed to certain light intensity. If only 1mg of CO2 enters the leaf in an hour, the rate of photosynthesis is limited due to the CO2 component which is also the limiting factor in this case.
The rate photosynthesis increases with the rise in the concentration of CO2. Any further increase in the CO2 concentration does not affect the rate of photosynthesis. It only increases if the intensity of light increases.
Criticism of Law of Limiting Factors
Blackman in his illustration of the limiting factor exhibited abrupt breaks in the rate of photosynthesis that was caused due to the low intensity of light.
This illustration was criticized by his coworkers James, Harder, and the others.
According to them, the rate of photosynthesis does not decline abruptly, but gradually, whenever one of the factors becomes limiting.
This is a result of all the chloroplast being not under the same environmental conditions.
The exposed chloroplasts receive more light and CO2 than the deep-seated ones.
If Blackman’s illustration is true and these factors are limiting, the photosynthesis will be affected only in some chloroplasts.
This will result in the gradual decrease of the photosynthesis rate.
FAQs on Law of Limiting Factor in Photosynthesis Explained
1. What is the Law of Limiting Factor in biology?
The Law of Limiting Factor states that the rate of a biological process is controlled by the factor that is in the shortest supply relative to the organism’s needs. This means even if all other conditions are optimal, the process will slow down or stop if one essential factor is insufficient.
- Proposed by F. F. Blackman in 1905.
- Commonly applied to photosynthesis.
- The limiting factor may change as environmental conditions change.
2. What is a limiting factor in photosynthesis?
A limiting factor in photosynthesis is any essential condition that restricts the rate of photosynthesis when it is in short supply. The three main limiting factors are:
- Light intensity
- Carbon dioxide concentration
- Temperature
3. Who proposed the Law of Limiting Factor?
The Law of Limiting Factor was proposed by F. F. Blackman in 1905. He observed that the rate of photosynthesis depends on several factors, but only the factor in the least amount at a given time controls the rate. This principle is also known as Blackman’s Law of Limiting Factors.
4. How does the Law of Limiting Factor affect photosynthesis?
The Law of Limiting Factor affects photosynthesis by determining which environmental factor controls its rate at a particular time. For example:
- If light intensity is low, increasing carbon dioxide will not increase photosynthesis.
- If light is sufficient but carbon dioxide is low, CO₂ becomes the limiting factor.
- If both light and CO₂ are adequate, temperature may limit the enzyme-controlled reactions.
5. Can you give an example of the Law of Limiting Factor?
An example of the Law of Limiting Factor is seen in a greenhouse where plants receive plenty of light but limited carbon dioxide. In this case:
- Light is abundant.
- Carbon dioxide is insufficient.
- The rate of photosynthesis remains low until CO₂ is increased.
6. What are the main limiting factors of photosynthesis?
The main limiting factors of photosynthesis are light intensity, carbon dioxide concentration, and temperature. Each factor plays a specific role:
- Light intensity affects the light-dependent reactions.
- Carbon dioxide is required for the Calvin cycle.
- Temperature influences enzyme activity.
7. What is the difference between Liebig’s Law and Blackman’s Law of Limiting Factor?
The difference between Liebig’s Law of the Minimum and Blackman’s Law of Limiting Factors lies in their application and scope.
- Liebig’s Law states that plant growth is controlled by the scarcest nutrient in the soil.
- Blackman’s Law states that the rate of a physiological process like photosynthesis is controlled by the factor in least supply.
8. Why does increasing one factor not always increase the rate of photosynthesis?
Increasing one factor does not always increase photosynthesis because another factor may already be limiting the process. For example:
- If carbon dioxide is low, adding more light will not increase the rate.
- If temperature is too low, enzyme activity slows down despite high light and CO₂ levels.
9. How can limiting factors be controlled in a greenhouse?
Limiting factors in a greenhouse can be controlled by optimizing environmental conditions for maximum photosynthesis. Common methods include:
- Providing artificial light to increase light intensity.
- Enriching air with carbon dioxide.
- Regulating temperature using heaters or cooling systems.
10. Is the Law of Limiting Factor applicable only to photosynthesis?
No, the Law of Limiting Factor is not limited to photosynthesis and applies to many biological and ecological processes. It can affect:
- Plant growth limited by nutrients.
- Population growth limited by food or space.
- Enzyme reactions limited by substrate concentration.
