In his book Anatomic Structure and Function, Dr. W. Ophuls described the relationship between structure and function as “the great biologic problem”(1). He describes how there is no set leader between the two; sometimes with function determining structure just as much as structure does the same likewise, in a way that would give finite limits to function. To Ophuls, the question in which one determined the other required a definite answer that was based partially on one’s view point and whether the particular structure could fulfill a niche in nature and thus, gain a purpose.
Ophuls, of course holds only one viewpoint on the matter; when he wrote the above, it was in the early twentieth century, and inevitably others have debated the matter since then. Despite this, the general consensus is that there is a definite relation between structure and function, and that the existence of such is vital.
Example 1 – moths
There have been suggestion that any phenomena that has a strong purpose can be explained purely by “mechanical cause and effect” (2)., however philosopher Immanuel Kant argued that through experience and interaction with its environment, a human mind was the single cause of how our anatomy is structured.
While one would argue that Kant pushed the idea to its extremes, a more reasonable suggestion would be that the structure of biological life could not be explained as a result of efficient design alone. One must note that both viewpoints stem from a time where a popular opinion thought of as fact was that “all Nature – the universe as a whole – is a personality whose total end is the perfection of all its parts” (3).
Now, most scientists think of processes such as evolution to lack a desire to reach perfection; phenomena such as drift and selection favor the passing of alleles that give an individual an advantage in life to offspring. A popular species to observe visible evolution in recent years is with Biston betularia, more commonly known as the Peppered moth. It is an example of selection pressures acting on the colour of the moth, increasing the allele frequency of a random mutation for a black moth (carbonaria) over the next few generations. Because of the abundance of carbonaria moths increasing during the industrial revolution, we can see that it seems more favorable for a moth to be black so as to better hide in the thick smog of industrial areas like Manchester. The change in the moth’s structure, in this case the amount of melanin it has, seems to act as a survival advantage in urban areas. The carbonaria moths are more successful at camouflaging themselves to avoid predation.
However the excess soot in the air of industrial areas has decreased in recent years due to the enforcement of burning clear fuels and the installment of Clean Air laws in England. Despite the rapid domination of carbonaria moths over typica moths (pale peppered moths) in the population, the former variety’s numbers has dramatically reduced since the Industrial Revolution during the 19th century.
If the idea that there was a set structure of every organism that meant it could function to maintain the best possible chances of reproducing was true, then we would expect that since an evolutionary advantage for carbonaria moths has been found then eventually the peppered moths species would lose all alleles that would result in a typica moth; however instead carbonaria moths began to be selected against and have now become the minority sub species. Surely, that would mean that the carbonaria moths are moving away from an ideal organism with “perfection of all its parts”, for it has not evolved in a linear path to whatever this pseudo ultimate organism may be.
What this tells us is that while a successful species may require a new function when the environment around it changes, the structure will be altered to support this requirement. If an individual is unable to carry out a function that would prevent death before it can successfully reproduce, then the alleles for the structure that has hindered it will be lost in the gene pool. What must be remembered is that while the pressures of evolution are ever changing over time, the link between structure and function will not lose its importance.
Example 2 Ecosystems
To demonstrate an example for this topic in the realms of macrobiology, let us look at ecosystems; now, this is a large umbrella term that includes both biotic and abiotic conditions, and can otherwise be thought of as a “complex in which habitat, plants and animals are considered as one interesting unit, the materials and energy of one passing in and out of the others”(4). Immediately we can see that an ecosystem by this definition has a clear structure, as describing it as a “complex” would suggest that the ecosystem is made up of multiple parts that are linked in a system or network.
On an even larger scale, individual ecosystems can connect to each other, for example a smaller ecosystem of dead logs can exist within the larger ecosystem of a rainforest (5). This also allows for a direct flow of energy between the systems, the logs decomposing into the soil and therefore supplying nutrients (after ammonia is formed and nitrification has occurred) for more plant matter in the rainforest to grow. That is an exchange of energy, similar to how a grazer gains energy from eating a producer in a food chain like grass, and loses energy through heat loss.
An undisputable fact is that all organisms need energy to function, be it metabolic heat, chemical, ect. Energy flow is unidirectional, so a producer cannot gain energy from a consumer in a food chain. As energy cannot be destroyed, structures within the ecosystem like a food chains serve the purpose of transporting energy between autotrophic (green plants that photosynthesise) and heterotrophic (other plants and animals that use autotrophs as a food source) components. There is an exchange of biomass between organisms.
For autotrophs, they are imperative for supplying oxygen for animals to respire with; by using light energy, autotrophs as the producers in a food chain photosynthesise and release oxygen as a waste product during the light dependant stage of the process. This is a vital occurrence because it is simply impossible for numerous land animals to survive without an atmosphere with a usable amount of oxygen for aerobic respiration. Without this, these organisms would have no sustainable, long term solution to produce metabolic energy, and therefore would not even be able to achieve a simple movement such as contracting their diaphragms for the mechanical process of breathing.
From this, we can deduce that there are three main functional components that form the working structure of an ecosystem; the organisms, the energy that enters the system from an external source (the sun) and the inorganic components (ie. nutrients, oxygen, ect.). We can also view the structure of the working ecosystem as being split into two processes, mineral cycling and the flow of energy. Both keep abiotic and biotic components in contact with each other so that organisms can openly interaction with their environment within their habitat and vise versa. Without this clear order, organisms would not be able to function enough to successfully produce offspring and pass on their genes, which is incredibly importance in sustaining life over more than one generation for that species.
Example 3 – The role of water
Conclusion
As stated in the title, the purpose of this essay revolves around the importance of structure and function, and as well can see in the examples used previously, what we mean by importance depends on the scale that we are looking at. We have specifically looked at examples that range from macro to micro so as to represent a wide view of biology, and so we can see that what is important about one structure in securing a function in the peppered moth is different to that in