Which statement best describes scientific laws?

A. Scientific laws are scientists’ opinions of why events occur in nature.

B. Scientific laws describe specific relationships in nature without offering an explanation.

C. Scientific laws explain why natural events occur.

D. Scientific laws were theories that have been tested, proven, and adopted as laws.

Diagram showing Mendels' laws
Diagram showing Mendel’s laws. Note the letters R, r, Y, y are all different alleles of the seed pod. R = green, r = yellow, Y = wrinkled, y = smooth.

The correct answer is D. Scientific laws were theories that have been tested, proven, and adopted as laws.

Scientific laws are less common than theories. This is because laws are actually theories that have been tested and proven over time. There are laws in the physical and biological sciences, but there are more in the physical sciences.

Determining if some relationship is a law is difficult since it relies to some extent on subjectivity. A scientist has to decide how much evidence is enough to justify designating a theory as a law. Saying that some relationship is a law implies consistency, and in fact, this is often not the case in biology.

There are a few biology laws that have been developed. For example, Mendel’s law of segregation and law of independent assortment. However, even though Mendel derived laws for how traits are inherited, it has been discovered that often these laws do not apply.

In other words, there are numerous exceptions to the rule. This may be why today scientists are reticent to state that something is a law. Laws are supposed to represent a constant relationship. Biological systems are complex and it is very difficult to find such relationships among variables.

The scientific method

Scientists follow a specific method when doing research. This is necessary to ensure objectivity. A hypothesis needs to be generated before any study begins.

This is really a statement that states the possible reason or explanation for some phenomenon that is observed. The methods are then designed in a way so as to test the hypothesis that is made.

Experiments should be designed so that there is a control in addition to the treatments that are tested. This is necessary because everything but the factor of concern needs to be controlled for. There also need to be enough replicates of each treatment in order for the statistical analysis to be used and to be valid.

After enough studies have been done in which the same result is obtained, then a theory can be proposed.  Theories need to be tested over a very long period of time before they can be considered to be laws. Thus, there are very few laws in biology.

There are studies that are based on observations in the field rather than experimentation. This was more common in the past, but today the tendency is to have experimental evidence that can be rigorously tested using statistics.

Scientific laws

Some laws apply to both the physical and biological worlds. This is the case for the laws of thermodynamics, which although developed to explain energy in physical systems, do also apply to systems in biology. Energy exchanges in living organisms follow these thermodynamic laws.

The first law of thermodynamics states that the amount of energy in the universe stays the same. This means that the total quantity of energy in reactants will be the same as the amount of energy in products and in the heat energy released during the reaction.

In other words, energy is never lost but simply converted from one form to another. This can be seen when we look at photosynthesis. The radiant energy from sunlight is converted in a plant into chemical energy, sugars.

During chemical reactions, some energy is converted to heat, thermal energy. The second law of thermodynamics states that systems tend to move towards disorder (entropy) when reactions occur. This is largely due to the heat that is released in reactions. In biology, energy is needed for systems to remain organized

Biological laws

Gregor Mendel derived genetics laws after studying the inheritance of traits in pea plants. He developed two laws to explain how specific characteristics of plants were inherited. The first law is the law of segregation.

This law states that alleles segregate independently into the sex cells or gametes. An allele is a form of a gene, so for instance, if we are looking at flower color then the color purple would be one allele and the color white would be a different separate allele.

Mendel ‘s second law is the law of independent assortment, which states that genes separate independently from one another into the sex cells. He noticed this when he was doing dihybrid crosses, which were genetic crosses involving two traits. This can be seen when looking at the seed pod shape and color.

In other words, just because a parent pea plant had a smooth shape and yellow color seed pod did not mean that the progeny would also have yellow and smooth seed pods.

In fact, the color and the shape of the seed pods assorted separately into the gametes. So for instance, a seed pod could be yellow and wrinkled, green and wrinkled, yellow and smooth, or green and smooth.

During Mendel’s time, genetics was not really fully understood and in fact, the traits were called factors. Many years after Mendel, researchers found out about genetics and how genetic recombination occurs in meiosis. This helped explain how independent assortment was possible.

Even when laws are developed in biology, they often have exceptions. This is the case with Mendel’s laws as today it is known that in many cases inheritance does not follow strict Mendelian rules.

Challenges in Biology

Biology has numerous challenges when it comes to deriving laws. It is difficult to find a constant relationship among variables when you are looking at biological systems.

Even if a scientist, such as Mendel, does derive a law, there are often a great number of exceptions that do not obey the rules. It is a problem finding predictability in systems which show tremendous variation.

It is very difficult finding a universally true relationship among variables, especially in living systems. This may be the reason that there are so few laws in the biological sciences when compared with the physical sciences.


  1. GWF Drake (2018). Thermodynamics. Retrieved from Encyclopedia Britannica.
  2. PK Dhar, A Giuliani (2010). Laws of biology: why so few? Systems and synthetic biology.
  3. RH Raven, RF Evert, SE Eichhorn (1987). Biology of plants, 4th edition. New York: USA, Worth Publishers.
  4. RL Dorit, WF Walker, RD Barnes (1991).  Zoology. Philadelphia: USA, Saunders College Publishing.
  5. OFG Kilgour (1982). Mastering Biology. London: UK, MacMillan Press.


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