Lecture 2: What is a Living Organism?

Editors note: This lecture is part of a series of lectures Prof. Kambadur Muralidhar gave at the University of Hyderabad in 2017, that he kindly shared with Club Sciwri. We will be publishing all the lectures, in parts, over the coming months. ~ Arunima

Biology is the science of living organisms. But what is a living organism?

How does it differ from an ‘inanimate’ object? It sounds easy to answer but as we will find out, it’s not that simple. From the beginning, man has been mystified by the phenomenon of living. Historically, there were two predominant views. One compared our body to a machine, where each machine works mechanically with coordinated moving parts. Each machine is ‘designed’, probably by God, and works as per the principles of physics to execute physiological and behavioral processes. The idea of a designer (God?) lurking behind these mechanistic ideas is inescapable. The other view believed that life is a ‘force’, which drives the action in the body, including thinking, and is variously labeled as soul, spirit, energy, prana etc. The location and material basis of the force within our body is not clear in the writings of those who proposed this idea. Ancient Greek, Indian, and Chinese philosophers speculated about the composition of objects in this universe. The Five Elements (Pancha Bhootas, like fire, earth, air, water, and ether) principle of an Indian thought is one such theory. However, these philosophies do not say what exactly is the ‘living’.

A commonly held idea among the simple-minded men and women about the living is that when you ‘insult’ a living organism it will react, unlike a non-living entity, which does not react. By this definition, a dog or a cockroach is living. In other words, all animals are living, but all plants aren’t! In a way this idea of ‘what is living’, is tantamount to saying that living organisms move voluntarily while non-living objects are stationary. Obviously this should be a wrong notion. Anybody who has studied biology at school level knows that living organisms have the ability to grow, reproduce, and to sense and respond to environmental cues/insults as characteristic features/properties. However, one should explain that inanimate objects like a sand dune or a crystal can also grow but by accretion, whereas living organisms grow by assimilation. Exceptions to these expected properties are found; and thus, this is not a defining property of living organisms.

Centuries ago, chemists raised a simple question regarding elemental composition of living organisms, and whether it differs from that of inanimate objects. Results indicated that there was no qualitative difference in elemental composition between a handful of top soil (example for non-living) and a tissue from say, a cockroach or a plant (example of living or even recently dead). Closer examination revealed that the relative abundance of carbon, hydrogen, oxygen, and some other elements was much higher in living tissue than in a sample of inanimate rock. Further, the types of compounds present in soil were mostly inorganic while those in living organisms were organic. In fact, the compounds found in nature (another loose term for living organisms) were called ‘Natural Products’.

When they raised queries about what these compounds do inside living organisms, they discovered ‘metabolism’. A new definition of living organisms came about that defined anything that exhibited metabolism as living!

The implications of this statement are tremendous.

Physicists who studied the manifested properties of natural objects/phenomena discovered the fundamental laws that explain the behavior of nature, for example, the Second Law of Thermodynamics, according to which all objects in this universe are subject to entropic doom. Existence of living entities that represent an ordered structure and process sounds improbable! Later, developments in open-system thermodynamics gave insight into the fact that living organisms are machines that extract energy from environment and keep themselves in a non-equilibrium steady state. ‘Death’ brings about equilibrium where the free energy change is zero! This gave a new definition for living organisms. However, we frequently come across ‘brain-dead’ patients in hospitals. The doctors declare the patient as dead but keep it alive artificially by a heart-lung machine. Of course, the patient’s family believes that the patient is alive.

Consciousness, or more correctly, self-consciousness becomes the definition of higher living organism. What is self, though? Here one enters the domain of Philosophy!

To summarize, we do not have a satisfactory and universal definition of the living! Man in his attempt to search for life on extra-terrestrial astral bodies may not even recognize them if the life forms were not carbon-based; perhaps aliens won’t recognize us either if their dimension-perception were not the same as ours!

Suggested Reading Material:

1. Muralidhar, K., as Chief Advisor (2005) Biology for 11th Class, NCERT publication, CBSE system of School Education and Exams.
2. Muralidhar, K., as Chief Advisor (2006) Biology for 12th Class, NCERT publication, CBSE system of School Education and Exams.
3. Muralidhar, K., (2014) Communications in Living Organisms, INSA Distinguished Lectures, (Ed) SK Saidapur, Indian National Science Academy, New Delhi.

Author

Prof. Kambadur Muralidhar is an Indian biologist, known for his work in biochemistry, endocrinology and reproductive biology. He taught at Delhi University for over thirty years, and was Head of its Department of Zoology. Currently, he is Jawaharlal Nehru Chair Professor, School of Life Sciences, University of Hyderabad. He is a Fellow of the Indian National Science Academy, the Indian Academy of Sciences, and the National Academy of Sciences, India. He is also highly regarded as a teacher and educator, and has contributed to biology education at both high school and college levels.

Editors

Arunima Singh, PhD edited, and Paurvi Shinde, PhD, proofread the article.

Arunima obtained her PhD from the University of Georgia, and is currently a postdoctoral researcher at the New York University. A computational structural biologist by training, she enjoys traveling, reading, and the process of mastering new cuisines in her spare time. Her motivation to move to New York was to be a part of this rich scientific, cultural, and social hub.

Paurvi is a recent PhD, in Biomedical Sciences (Immunology) with expertise in T cell activation pathways. She currently works as a Postdoctoral Fellow at Bloodworks Northwest in Seattle, where she studies the mechanism of how alloantibodies are formed against ‘non-ABO Red Blood Cell antigens’. Apart from science, she loves editing scientific articles to convey the message behind it, in a clear and concise form.

Artist

Ipsa provided the cover image. She is a post-doctoral fellow at Instem, Bangalore. She tries to communicate science through visual arts as a medium. Collecting graphic books, tree trash, and reading brain pickings is few of her favourites. Follow and purchase her artwork at Ipsawonders (Facebook, Twitter, and Instagram).  She will be happy to hear praises and non-praises at ipsajain.31@gmail.com.

Other images in the blog courtesy Pixabay.

Blog design: Arunima Singh

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