Living world and living things are quite mysterious. This is the reason scientists are trying to unfold the mystery of nature by constantly discovering new things from centuries till date. Be it a different variety of flowers, forests, and organisms. But the major question which I am sure strikes everyone is what is living and what makes it different from non-living? What does the word living mean and how can we define it? Now let’s tackle this question and clearly understand about living and living things in details.
Characteristics of Living Things
There are certain distinctive characteristics by which we try to define “living.” The characteristics include growth, metabolism, reproduction, self-organize, self-replicate, interact, ability to sense and react are some very essential features of living things/organisms. Let us discuss these traits in details.
Living things tend to grow in size. However, there are some non-living things capable of growing in its size. So, what is the difference in both? The Growth of non-living things is primarily driven by the accumulation of matter from external factors or outside.
However, growth in living things is because of different internal processes occurring inside the body of the living organisms mainly because of the formation of new cells. The increase in number and mass of individuals are two unique characteristics of growth.
Multicellular organisms exhibit growth by cell division. Growth varies in plants and animals. While animals exhibit definite growth and animals cease to grow after a certain age, plant exhibit indeterminate growth and the cells continue to divide during the entire lifespan.
If we consider unicellular organisms, they tend to grow in size by cell division. Moreover, this can be easily detected by counting the cells during in vitro cultures under a microscope. However, growth and reproduction are separate processes as we gradually move to higher multicellular organisms (plants and animals).
However, we define growth as an increase in the body mass. Thus, non-living objects can also grow. For instance, boulders or sand mounds grow by addition of the material on the surface. Therefore, in living organisms growth is from within whereas in non-living things growth is from outside. Thus, growth cannot be the determining property for determination of living organisms.
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Living organisms exhibit another property-reproduction. But can it be the only determining criteria of living things? Let us find out. Reproduction is an essential feature by which living organisms reproduce its own kind in order to continue the progeny of the species.
Reproduction can primarily of two types-sexual reproduction and asexual reproduction. Most of the times, the offspring possess similar features as that of parents. Reproduction generally refers to sexual reproduction. Asexual reproduction is used by the lower organism for division or reproduction by asexual means.
For example, fungi undergo asexual reproduction to multiply and divide by the production of asexual spores. Hydra reproduces by budding or flatworms (planaria) undergo regeneration from a fragmented part to regenerate the lost part of the body and form an entirely new organism. Similarly, for unicellular organisms like bacteria, amoeba, etc. reproduction and growth are synonymous with each other.
Growth & Reproduction
Growth is the increase in the number or mass of cells. However, reproduction in case of unicellular organisms is also achieved by an increase in cell number. Thus, growth and reproduction are synonymous and cannot be the distinguishing factor. Moreover, there are many organisms such as worker bees, mules, infertile human couples that cannot reproduce. Therefore, reproduction cannot act as the defining and distinguishing factor of living organisms even though non-living object cannot reproduce by itself.
Another important feature of living organisms is metabolism. Chemicals form the basis of every living organism and these chemicals belong to the different size, functions, classes that are constantly changing and converting to form other biomolecules. The sum total of the chemical reactions involved in the biological processes is collectively termed as metabolism. It falls into two primary categories:
- Anabolism- the synthesis of any compound such as photosynthesis
- Catabolism- the breakdown of any compound such as respiration
Numerous metabolic reactions occur simultaneously in any living thing irrespective of plants, animals, and microorganisms. However, non-living things do not exhibit metabolism. If a reaction occurs outside a body of the organism then the organism is neither living nor non-living.
Thus, this indicates metabolism is the defining characteristics of living organisms. Therefore, the cellular organization of any organism is the defining feature of every life form.
Response to External Stimuli
One of the complex features of living things is the potential to sense the environment or surroundings and respond to environmental stimulus. Environmental stimulus can be chemical, physical and biological. Living things have particular sense organs and through the sense organs, it responds to external factors like water, temperature, light, pollutants, other organisms, food, etc.
Living organisms have a tendency to respond to external stimuli such as heat, light, chemicals, and sometimes even to other organisms. This characteristic of the living organism is essential for the survival of living things. For instance, if we consider food as external stimuli, an animal will respond to it accordingly to take up the food for the animal’s survival. Survival of any organism requires nutrition, hence the presence of food make any organism respond to it accordingly.
Thus, all organisms are aware of their environment but human beings are aware of themselves. Hence human beings have self-consciousness. Thus, consciousness is also an important defining property of living things.
However, it is very complicated to define living in case of human beings. For example, there are people who are in the coma and they do not respond to external stimuli. They function of heart and lungs are replaced by machines. So, are they living or non-living? Thus, defining “living” in human beings is complex.
Therefore, “summing up living things are constantly evolving, self-replicating, and self-regulating interactive complex systems that are capable of responding to an external stimulus.”
Solved Examples for You
Question: Definition of Biosystematics
- The classification of organisms on the basis of broad morphological features
- Classification and arrangement of living things based on cytological characters
- Establishment and delimitation of various taxa of organisms and their relationships with each other
- The classification of living organisms on the basis of the evolutionary history and the establishment of phylogeny based on the complete set of different parameters established from different fields of studies.
Solution: Option 4