Would you be astonished by the fact that the viruses are neither considered as alive nor hold the status of a living being despite the capability of infecting millions of people and its potential to kill?
However, there are other non-living things such as weapons, radiations, etc. adequate to take human life. But the difference is unlike the viruses, those objects don?t just spread from person to person. They are not effective by itself and they are in control by the deliberate actions of someone.
Most natural calamities are constrained by area: an earthquake that strikes in India do not affect France, at least directly.?
?Viral infections extend from the mild seasonal flu to deadly Ebola viral disease (EVD). The viral infection by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing the COVID-19 claimed 106138 lives with 1699595 confirmed cases so far in 213 countries.
Viruses are diverse in size, shape, host range and indeed in the type of the cell, they infect in a host.
Size of the virus
Viruses are smaller than bacteria (the smallest bacteria is 0.2 ?m in diameter). Viruses range from 20 nm to 250-400 nm.
A bacteriophage which is a virus infecting the bacteria range in size from 20 to 300 nm and is 10 to 100 times smaller than most bacteria. Many bacteriophages can infect and reside inside a single E.coli (1-2 ?m long and 0.5 ?m in radius), the bacteria that causing urinary infections and food poisoning. Though there are a few viruses such as mega virus which are discovered recently are larger than the bacteria.
The smallest animal viruses such as parvovirus are 18 to 26 nm and the picornavirus is 25 to 30 nm in size. The poliovirus, a highly infectious virus invading the nervous system causing paralysis in hours is 30 nm in diameter which is 10000 times smaller than a grain of salt.
The shape of the virus
Viruses are weird with different unique shapes. The bacteriophages (bacteria infecting viruses) bear resemblance to lunar landers with their spider legs. Animal viruses for example coronavirus, herpes simplex virus, etc appear like porcupines with their glycoproteins spiking out. Some other viruses, for instance, papovavirus, parvovirus look like a geodesic dome. Plant viruses such as potyviruses, carlavirus seem like a worm.
Viruses infect almost all living beings including plants, animals, humans, and bacteria. Viral infections in plants, let’s say tobacco mosaic virus, cucumber mosaic virus, etc results in crop loss and decrease in yield affecting the agriculture extravagantly. On the other hand animal husbandry, aquaculture and animal breeding are also affected defectively by the viral invasion.
Viruses infect humans ranging from mild flu to fatal ones primarily and most importantly impacting the health. Viruses even infect the bacteria.
Are viruses alive?
In a nutshell, viruses are a common element of human experience affecting the health, finance, economy, agriculture and many industries. On picking up a viral infection, one would contemplate it as under attack.
Nevertheless, it is an open-ended question in the scientific community. By all means, viruses do impact our lives in the above-mentioned ways despite being not alive!
We, humans, like to classify objects in our physical world and that makes our life easy. Nonetheless, the complexity lies when this classification is categorical, just living and non-living things. We are skeptical about the place something holds that doesn?t belong to either of these two categories.
Let?s define life?..
What is life?
We all are living beings and we live life. The exact definition of life is hard to comprehend. Quality of life is often reviewed in diverse perspectives such as concerning physical health, family welfare, education, employment security, wealth, social connectedness, safety, freedom, religious beliefs, and leisure/recreation.
Furthermore, what is life with regard to biology?? Certain unique qualities define life in the biological context. They are
- Energy utilization
- Response to environment
- Genetic material
Birth and reproduction
Start from the start?. You have to be born to have a life, it is that simple! All living beings are born.
All mammals including humans reproduce?sexually through internal fertilization and give birth to offspring of their kind. Similarly, birds and reptiles also reproduce by internal fertilization during which the eggs are fertilized inside the female, females lay eggs and the hatchlings are produced, though some reptiles are capable of asexual reproduction. Moreover, amphibians reproduce?sexually with either external or internal fertilization and the larvae go through metamorphosis to change into an adult.
The asexual method of plant reproduction includes fragmentation, budding, spore formation, and vegetative propagation. Sexual mode of plant reproduction involves the fusion of male and female gametes producing seed or fruit and a whole new plant is produced from that.
Though it may seem strange, bacteria also reproduce. Bacteria are reproduced by binary fission, the mother cell is divided into two daughter cells and each daughter cell is the clone of the mother cell.
But this doesn?t go with the virus. Viruses are neither born from a parent nor divided from an existing cell. On the contrary, viruses are assembled like a machine or a robot.
Undoubtedly, numerous viruses are formed from a single virus. However, unlike the animals, plants, and bacteria, a whole new offspring or cell is not produced in the case of the virus. Individual components of the virus are produced and all these components are assembled to form the virus. In that instance, viruses are not born and they don?t reproduce though they can replicate the genome and assemble their parts.
Living things grow
All living beings including humans, animals, plants and even bacteria are usually small when they are born and they grow with time. Growth is an increase in size and mass of the organisms and during the process of growth, the organism develops. Growth is an important entity in the life cycle of organisms help them achieve reproductive success, differentiate themselves, find their niche, etc. The kind and rate of growth vary among the species and even among the individuals in a species.
Notwithstanding, the virus fails here again. It doesn?t have growth. It is always the same.
Every living thing requires energy. Plants are autonomously producing the energy they require from photosynthesis and utilize that energy for its biochemical requirements, growth, reproduction, etc. Animals including humans consume by eating food and the food is converted into energy by their body. Indeed bacteria utilize to take up the nutrients around them and produce energy.
In essence, all living beings have biochemical autonomy.
Conversely, the virus doesn?t require energy or consume energy. However, the virus-infected cells need the energy to replicate the viral genome and to produce virions.
Respond to environment
A well-known example of stimuli is phototropism, where plants grow towards light and if the light direction is changed, plants would also change the direction of growth responding to the light.
Supposedly if the snails encounter something offensive, it will respond by retracting its whole body inside its shell.
Having said that, a rock remains still and the same in whatever ways its environment changes as it is a non-living thing.
From my standpoint, the virus takes a neutral approach here. The virus cannot move or respond to environmental stimuli precisely like plants and animals. Yet, the virus can cause mutation in its genetic material, thereby increasing the chances of survival and adapting to the environment.
Every single organism possesses genetic material that is the blueprint of their life. Human beings have their genetic material determining their traits and behaviors. The genome of the bell pepper plant decides what color bell pepper to produce.
The rock is a non-living object and doesn’t have genetic material. But the virus has already signed up for this advantage. The virus has genetic material and the genome of the virus consists of either DNA or RNA.
Furthermore, the genome of the virus determines most of its properties.
All living things die probably due to malfunctions in their body or because of old age. Even the bacteria can die off nutrient depletion.
Not the virus!? Again it?s strange to talk about death if not born. Therefore, viability and maintaining the infectivity would be a better term in the case of viruses.
Outside the host, the virus can be divided into two. Viruses that remain
- Intact and remains infectious
- Identifiable-enough genetic material to be identified, but is no longer capable of attaching to host cells (therefore possessing no harm)
Different viruses have different survival rates outside the host.
Viruses have diverse surface survival rates. The type of surface, environmental temperatures and humidity all come into play in determining the surface survival of viruses.
Report card of the virus
Objects to be classified as living things should fulfill all the above mentioned biological qualities of life. Plants, animals, and bacteria accomplish all those qualities and are categorized as living things.
A rock doesn’t comply with any of those qualities and is a non-living thing.
But what is the score of the virus? The virus partially fulfills the criteria. In this scenario, what is the likely place of the virus in the living-nonliving category?
There are different voices on this matter. Viruses were first identified as filter passing substances causing disease and were considered as the smallest living entities capable of infection. Later on, viruses were addressed as biological chemicals as they have genetic material but they parasitize almost every aspect of their life cycle.
Viruses hold a special place in the tree of life, though they don?t fit in our conventional sense of classification system of life.
But that?s life again; we humans can?t force everything to fit in our criteria.