Living World

A living thing relates to any organism or a life form that possesses or indicates the traits of life or being alive. Their  essential traits are as follows: having a prepared structure, requiring energy, responding to stimuli and adapting to environmental changes, and being able of reproduction, growth, movement, metabolism, and death. Currently, living things are categorised into 3 main Domains: (Eu)Bacteria (true bacteria), Archaea (archaebacteria), and Eukarya (eukaryotes).Unicellular organisms develop in wide variety via means of cell division. 

When growth occurs constantly in the life span of plants. It is indeterminate growth (unlimited growth). When growth occurs only to a certain age as in animals, its determinate growth (limited growth). However, cell division takes place in certain tissues to replace lost cells. Non-living objects also grow via increase in body mass. Mountains, rocks and sand do grow. This type of growth exhibited via non-living objects is by collection of materials on the surface is known as accretion. In living organisms, growth takes place from within.

Origin of life

The Primordial Soup

The “primordial soup” refers back to the hypothetical version of the primitive Earth in which the collected organic material and water resembled a soup. This soup acts as a site where organic compounds have synthesized. This is a widely-accepted research model of the Miller–Urey experiment. Apparently, the simulated-primitive Earth favoured the chemical synthesis of the primary structure of the cell membrane (e.g. phospholipids forming lipid bilayers) and organic compounds from inorganic sources. The primordial soup is likewise the edict of the heterotrophic concept of the beginning of life proposed by Alexander Oparin and John Burdon Sanderson Haldane.

Characteristics of living things

Living things are organisms that display the traits of being alive. What separates living things from nonliving things is the subsequent traits:

An organised structure

Living things are believed to have an  organized structure. It can be single-celled which includes a bacterial cell, or multicellular including animals and plants that are made up of several cells. A cell is the essential biological unit of an organism. Various cellular processes are carried out via the cell in an orchestrated, systematized manner. 

Energy Requirements

Living things require energy for survival. Energy is very vital as it serves numerous metabolic activities of a cell. One way that organisms synthesize energy is via photosynthesis where light energy is converted into chemical energy. Another is via cellular respiration in which biochemical energy is harvested from an organic substance (e.g. glucose) and, then, saved in an energy-carrying biomolecule which includes ATP for later use.

Reproductive capacity

A living thing is able to reproduce offspring. There are two ways via means of which living things can reproduce: sexual reproduction and asexual reproduction. In sexual reproduction, male and female sex cells of the two parents unite and form a zygote that further develops into a being of their own kind. Asexual reproduction, in contrast, is a way of reproduction, that does not involve sex cells. The offspring comes from only one parent. Examples encompass binary fission, budding, vegetative propagation, sporogenesis, fragmentation, parthenogenesis, etc.

Growth

As we all know, all living things grow. At the cellular level, growth can be referred to as an increase in number or to an increase in size. The increase in the number of cells is via cell division. The stem cells of animals and the meristematic cells of plants divide to form new cells. As for the increase in cell size, it is because of the increase in cytoplasmic mass.

Metabolism

All living things metabolize. Metabolism refers to the numerous processes that are responsible for the keeping up of the living state of a cell or an organism. Examples of those involved in cell growth, respiration, reproduction, response to stimuli, sustenance, biomolecular syntheses, waste elimination, and different homeostatic processes.

There are two different varieties of metabolism: catabolism and anabolism. In catabolism, living things perform degradative chemical reactions that result in the breaking down of complex molecules into simpler molecules and obtain energy that is produced during the process. In anabolism, energy-related chemical reactions build molecules from smaller units.

Responsive to stimuli

Living things respond to stimuli and adapt to environmental adjustments. It can detect changes within the environment, especially by cells that function as receptors. For instance, humans have 5 essential senses: sight, hearing, smell, touch, and taste. Apart from detecting changes in its surroundings, it could additionally adapt to those changes.

Movement

All living things move. Since a living thing can detect stimuli from its surroundings, it responds accordingly. For example, animals move in search of prey, escaping predators, and movement for seeking a potential mate. While animals can move at will, plants have a rather limited form of movement.

Death

Living things die. A living thing has life and this life ends gradually. Senescence refers to organic aging. It is when living things gradually weaken over the course of their life. The organism progressively loses its capacity to function and deals with stress. As such, it becomes more vulnerable to diseases and dysfunctions.

Classification

Living things were previously classified into plants or animals. While each animal and plants life are eukaryotic, they are totally distinguished based on their defining characteristics, e.g. in terms of ability to move, mode of nutrition, and cellular features.

The major differences between bacteria and archaea are described as follows: one of their differences lies in RNA polymerase. Archaea includes ten subunits. Whereas, bacteria includes four. Another example is the composition of the cell wall. Archaea cell wall lacks peptidoglycan whereas bacterial cell wall contains peptidoglycans.

At present, the modern

taxonomy includes the classification of living things into three domains: 

(1) domain Eukarya, 

(2) domain Bacteria, and 

(3) domain Archaea. 

The seven major taxonomic ranks in descending order, are as follows:

Domain » Kingdom » Phylum » Class » Order » Family » Genus » Species

Domain Eukarya consists of all living things that are eukaryotic. These include animals, plants, fungi, algae, and protists. They contain membrane-bound organelles within their cells.

Conclusion

All living phenomena are due to underlying interactions. Properties of tissues are not present in the constituent cells but arise as a result of interactions among the constituent cells. Similarly, properties of cellular organelles are not present in the molecular constituents of the organelle but arise as a result of interactions among the molecular components comprising the organelle. These interactions result in emergent properties at a higher level of organisation. This phenomenon is true in the hierarchy of organisational complexity at all levels. Therefore, living organisms are self-replicating, evolving and self-regulating interactive systems capable of responding to external stimuli.