What is Meant by Characteristics of Life?

Biology is the science that investigates life. Defining life forms is not always easy. Every organism tends to exhibit certain features that distinguish living and non-living forms. Some significant characteristics of life include genetic code, evolution, cellular organization, irritability, respiration, movement, regulation, homeostasis, growth and development, adaptations, and response to stimulus.

What is Life?

Not all scientists agree on what constitutes life. Most living beings have a variety of characteristics, which we'll explore below. However, you can probably think of one or more examples where the rule is broken, such as certain non-living things being classified as living, or in some cases, living beings classified as non-living for most of the characteristics listed below. Virology, for example, is a branch of biology that studies viruses, which share certain characteristics with living organisms but lack others. Viruses, despite their ability to infect living organisms, cause diseases, and even replicate, do not follow the requirements used by biologists to describe life.

There is no single attribute that distinguishes a living thing from a non-living thing. The cat moves, but a car does as well. A cloud, like a tree, increases in size. A cell, like a crystal, has a structure. The term "life" is described by biologists as a set of characteristics that all living things share. The term "alive" refers to something that possesses all of the attributes of life. Life is distinguished with the help of a phylogenetic tree to explain the similarities and differences between different organisms.

"Living organisms in different levels"

Different Characteristics of Life

The term "organism" refers to a single living being. Living organisms share a number of traits.

Order, sensitivity or reaction to the environment, reproduction, growth and development, homeostasis, and energy processing are all key characteristics or functions or life processes shared by all living organisms. These traits, when considered together, help to describe existence.

"Different characteristics of life"


Organisms are complex, coordinated systems made up of one or more cells. Also, single-celled organisms are surprisingly complex; atoms within each cell form molecules, which in turn form cell organelles and other cellular inclusions.

In multicellular organisms that are made up of many cells, similar cells form tissues, and tissues in turn form organs that perform distinct functions. All the organs work together and form organ systems.


Organisms respond to a variety of stimuli. Plants, for example, have the tendency to bend toward a source of light, climb on walls and fences, and also respond to different types of contact.

All living things respond to their surroundings. A rock will simply lay there if you step on it, but if you step on a turtle, it can jump or even snap at you. Living things are aware of their surroundings and respond to changes in the world. The process of becoming accustomed to a new environment is referred to as adaptation. Structural, physiological, and behavioral characteristics that increase an organism's chances of survival and reproduction are examples of adaptations.

Even bacteria will respond to surroundings. Chemotaxis is defined as the bacteria’s ability to switch toward or away from the light or chemicals. When the bacteria moves toward a stimulus, it is referred to as a positive response. In case of a negative response, the bacteria move away from it.


Reproduction can be classified as asexual and sexual. Sexual reproduction is the mechanism that occurs by combining half of the DNA (deoxyribonucleic acid) obtained from each parent. In the case of asexual reproduction, an offspring produced by the single cell is an identical copy of itself. A strawberry is an example of an organism that uses asexual reproduction.

Growth and development

All living organisms have the potential to modify and evolve. A seed, given the right circumstances, will sprout and develop into a seedling, which will eventually become a larger plant. Of course, a pebble, which may look similar to a seed, will not grow in the same way.

Even the tiniest bacteria must evolve in order to survive. Bacteria are single-celled or unicellular prokaryote that reproduce by first duplicating their DNA and further dividing equally. This helps the cell to prepare for forming two new cells. If the parent bacterium does not evolve, the next generation of offspring that are reproduced will simply be smaller than the previous one. The bacteria would eventually become too small to function properly.

In the case of eukaryotes, which are multicellular in nature, growth and development are achieved via cell division. There are two types of cell division: meiosis and mitosis. Meiosis is used to produce sex cells and mitosis is involved in the production of new body cells for healing and growth.


Even the tiniest organisms have several regulatory mechanisms in place to organize internal functions, react to stimuli, and cope with environmental stresses. Blood flow and nutrient transport are some examples of internal functions that are regulated in the living organism. Organs, which are the set of tissues that function together within an organism, bring oxygen across the body, keep the body cool, provide nutrients to all the cells, and remove waste.


Cells require certain specific conditions in order to exhibit proper functioning. These include the right pH, temperature, and chemical concentrations. However, these conditions are capable of shifting from one moment to another. With the help of homeostasis (literally, "steady-state"), organisms exhibit the ability to maintain a constant internal environment or internal conditions within a narrow range, despite changes in the environment.

For example, the body temperature of an organism must be regulated by a mechanism called thermoregulation. Cold-climate organisms, such as the polar bear, have body systems that help them survive cold temperatures and retain body heat. Fur, feathers, blubber, and fat are all structures that help with insulation. In hot climates, animals have mechanisms for shedding excess body heat (such as perspiration in humans or panting in dogs).

Negative feedback loops play a significant role in maintaining homeostasis. This helps in self-stabilizing the systems. For example, when the temperature of the body is extremely high, this loop helps to bring down the temperature within the targeted value.

"Negative feedback loop for blood sugar level"

Energy processing

Every organism requires energy to perform its functions, and for that, every species needs a source of energy. The source varies depending on the organism. Some species, including plants, absorb solar energy and transform it into organic molecules, including glucose in food. This process is termed photosynthesis. These plants are called autotrophs, as they have the ability to prepare their own food with the help of the energy obtained from chemicals and sunlight.

Certain others, such as animals, use chemical energy obtained from the molecules that they ingest as food, which is referred to as metabolism and cellular respiration. Metabolism is defined as the summation of all the chemical reactions occurring in the body.

Levels of the Cellular Organization of Living Organisms

Highly structured and organized living organisms follow a hierarchy that can be determined and examined on a scale from small to large. The most fundamental and smallest unit of matter is termed the atom. It consists of a nucleus surrounded by electrons. Atoms form molecules. A molecule is defined as a chemical structure that consists of at least two atoms. These are held together by one or more chemical bonds.

Many biologically important molecules are macromolecules, which are large molecules created by polymerization. A polymer is a large molecule that is made by combining smaller units called monomers, which are simpler than macromolecules. DNA is an example of a macromolecule since this nucleic acid provides the instructions for the structure and function of all living organisms.

Organelles are macromolecule aggregates and are usually membrane-bound. These are found in certain cells. Organelles are microscopic structures found inside cells. Organelles, such as mitochondria and chloroplasts, perform vital functions. Mitochondria generate energy to power the cell, whereas chloroplasts allow green plants to use the energy in sunlight to produce sugars. Cells are the smallest fundamental unit of structure and function in living organisms.

Context and Applications

This topic is significant in the field of biology and evolution. This also helps in the professional exams for both undergraduate and graduate courses, specifically for courses such as:     

  • Bachelor’s degree in biology
  • Master’s degree in biology
  • Doctoral degree in evolutionary biology

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