What is a Living Thing? Characteristics and Examples
A living thing is any organism that exhibits the characteristics of life, such as growth, reproduction, response to stimuli, and adaptation to the environment. Living things can be classified into different groups based on their similarities and differences, such as animals, plants, fungi, bacteria, and archaea.
In this article, we will explore the definition of a living thing, the characteristics that distinguish living things from non-living things, and some examples of living things in different domains of life.
Definition of a Living Thing
A living thing is an organism that has the capacity to perform the following functions:
- Growth: Living things can increase their size and complexity by adding new cells or changing the structure of existing cells.
- Reproduction: Living things can produce new individuals of the same kind, either sexually (by combining genetic material from two parents) or asexually (by splitting or budding).
- Response to stimuli: Living things can detect and react to changes in their internal or external environment, such as light, temperature, pressure, chemicals, or predators.
- Adaptation: Living things can modify their structure or behavior to better suit their environment over time, through natural selection or genetic engineering.
- Metabolism: Living things can convert energy and matter from one form to another, such as breaking down food into simpler molecules or synthesizing complex molecules from simpler ones.
- Homeostasis: Living things can maintain a stable internal condition despite changes in their external environment, such as regulating their temperature, pH, water balance, or blood pressure.
These functions are essential for the survival and evolution of living things. However, not all living things perform these functions in the same way or at the same level. For example, some living things can grow faster than others, some can reproduce only once in their lifetime, some can respond to more stimuli than others, some can adapt more quickly than others, some can metabolize more efficiently than others, and some can maintain homeostasis more easily than others.
Characteristics of Non-Living Things
Non-living things are objects or substances that do not exhibit the characteristics of life. They may have some of the properties of living things, such as shape, color, texture, or movement, but they do not have the capacity to perform the functions of living things. For example:
- A rock may have a shape and a color, but it cannot grow, reproduce, respond to stimuli, adapt to the environment, metabolize energy and matter, or maintain homeostasis.
- A car may have a shape and a movement, but it cannot grow, reproduce, respond to stimuli, adapt to the environment, metabolize energy and matter, or maintain homeostasis without human intervention.
- A virus may have a shape and a reproduction (by infecting host cells), but it cannot grow (by itself), respond to stimuli (by itself), adapt to the environment (by itself), metabolize energy and matter (by itself), or maintain homeostasis (by itself).
Therefore, non-living things are not considered as organisms or living things.
Examples of Living Things
Living things can be classified into different domains of life based on their genetic and cellular features. The three domains of life are:
- Bacteria: These are single-celled prokaryotes that have no nucleus or membrane-bound organelles. They are found in almost every habitat on Earth and can perform various metabolic processes. Some examples of bacteria are Escherichia coli (E. coli), Streptococcus pneumoniae (pneumonia), and Cyanobacteria (blue-green algae).
- Archaea: These are also single-celled prokaryotes that have no nucleus or membrane-bound organelles. They are distinct from bacteria in their genetic and biochemical features. They are mostly found in extreme environments such as hot springs, salt lakes, or deep-sea vents. Some examples of archaea are Methanogens (methane producers), Halophiles (salt lovers), and Thermophiles (heat lovers).