Exploring the Second Law of Thermodynamics in Living Systems

The second law of thermodynamics, which posits that in an isolated system, the total entropy can never decrease over time, poses a fascinating challenge when considering the workings of living organisms. Despite the non-isolated nature of living systems, which exchange energy and matter with their surroundings, they still manage to maintain a relatively low internal entropy. How can we justify the application of the second law of thermodynamics to these complex and dynamic systems?

Living systems, far from being in isolation, actively participate in a continuous energy and matter exchange with their environment. This interaction allows them to maintain a steady state of order and functionality, while still alignment with the second law at a broader scale. Let's delve into how this contradiction can be resolved and why it is indeed consistent with the second law of thermodynamics.

Local Decrease in Entropy

One way to reconcile the second law of thermodynamics with the functioning of living systems is by understanding that these organisms can create local decreases in entropy over time. Living organisms take in energy from their environment and use it to grow, reproduce, and maintain their internal structures. For instance, plants convert sunlight into chemical energy through the process of photosynthesis, transforming less ordered forms of energy, such as sunlight and carbon dioxide, into highly ordered structures like glucose and starch.

This transformation is possible because living systems are not isolated entities but are constantly exchanging energy and matter with their surroundings. They harness and channel energy from their environment to perform complex functions and maintain order within their systems. This is a key concept in biological thermodynamics, where the internal entropy can decrease as long as the overall entropy of the universe increases.

Energy Flow and Entropy

A fundamental aspect of life is the continuous transfer and utilization of energy. Living systems depend on external energy sources such as food, sunlight, and other forms of exergy to perform their biological functions. The processes of respiration, digestion, and metabolism are energy-intensive activities that require the input of external energy to maintain a low internal entropy.

While living systems can decrease their internal entropy through energy absorption and conversion, they do so at the expense of increasing the entropy in their surrounding environment. For example, when organisms metabolize food, the chemical reactions release heat into the environment, which contributes to the overall increase in entropy outside the organism.

Heat Production and Entropy

The metabolic processes that sustain life, such as cellular respiration and photosynthesis, release heat and other forms of waste into the environment. This exothermic process is an inevitable consequence of the energy transformations occurring within the organism. The release of heat and waste products is a significant factor in the increase of entropy in the surroundings, thereby maintaining the overall balance with the second law of thermodynamics.

Complexity and Evolution

Evolutionary processes also play a crucial role in understanding the relationship between living systems and the second law of thermodynamics. As biological systems evolve and become more complex, they require a continuous input of energy to drive these changes. This evolutionary complexity arises from the integration of external energy sources, such as solar radiation, into the system.

Although the increase in complexity of biological systems might appear to be a local decrease in entropy, it is important to recognize that this increase is accompanied by a corresponding increase in entropy in the environment. The overall entropy of the universe remains unchanged or increases, aligning with the second law of thermodynamics.

Chemical Reactions and Entropy

Many metabolic and synthetic processes in living systems involve chemical reactions that can either decrease or increase entropy. For example, the synthesis of complex molecules such as proteins and nucleic acids from simpler ones decreases the local entropy of the system by creating more ordered structures. Conversely, the breakdown of high-energy molecules, such as the utilization of glucose, and the release of waste products into the environment increase the entropy of the surroundings.

These reactions illustrate the delicate balance between the internal and external entropy of the living systems. By harnessing external energy, living organisms can maintain a lower internal entropy, but they do so at the cost of increasing the entropy of their surroundings. This mechanism ensures that the overall entropy of the universe remains in accordance with the second law of thermodynamics.

In conclusion, the second law of thermodynamics is not violated in living systems; rather, it is upheld through a delicate interplay between local decreases in entropy and the corresponding increases in entropy in the environment. Living systems can reduce their internal disorder by taking in energy from their surroundings and utilising it for essential processes, but this occurs within the broader framework of the second law of thermodynamics which mandates an increase in the overall entropy of the universe.