Characteristic of Living Organisms

Characteristic of Living Organisms

1. Introduction

  • Biology is the science of life forms and living processes.
  • The living world comprises an amazing diversity of living organisms.
  • Life is a unique, complex cellular organization of molecules.
  • According to Lamarck (1809), nobody can have life if its constituent parts are not cellular.
  • Various types of chemical reactions, which lead to the availability of energy, growth, Development, responsiveness, adaptation, and respiration are shown by the cells composing life.
  • Life is a unique, complex organization of molecules expressing it through chemical reactions which lead to growth, development, responsiveness, adaptation and reproduction.

2. What is ‘Living?’

“In biology, an organism is any living system (such as animal, plant, fungus, or micro-organism). In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homeostasis as a stable whole.”

3. What is ‘Life?’

“Life (cf. biota) is a characteristic that distinguishes objects that have self-sustaining biological processes from those that do not either because such functions have ceased (death), or else because they lack such functions and are classified as "inanimate.”

4. Characteristics of Living Organisms

  • The various traits shown by living beings are as follows-

4.1 Growth

  • Growth is an irreversible increase in the mass and cell number of an individual.
  • A multicellular organism increases its mass by cell division.
  • In plants, growth continues throughout life as they have meristematic areas where cell divisions occur regularly.
  • In animals, growth occurs to a certain age after which cells divide only to replace worn out and lost cells.
  • Unicellular organisms also grow by cell division.
  • In higher animals and plants growth and reproduction are mutually exclusive.
  • Living organisms show internal growth due to the addition of materials and the formation of cells inside the body.
  • Such a method is called intussusceptions (L. intus-within; suscipere-to receive).
  • An increase in body mass is considered growth.
  • Non-living objects also grow if we consider an increase in body mass, but this growth is due to the accumulation of material on the surface. Examples- Growing of mountains, boulders, and sand mounds. 

4.2 Reproduction

  • It is the formation of new individuals of a similar kind.
  • Life arises from pre-existing life.
  • Reproduction may be sexual or asexual.
  • Fungi reproduce through millions of asexual spores.
  • Yeast and Hydra reproduce through budding.
  • In Planaria process of regeneration is found.
  • Filamentous Algae and Mosses reproduce by fragmentation.
  • Unicellular organisms reproduce through binary fission.
  • No non-living object can reproduce or replicate by itself.

4.3 Metabolism

  • All organisms are made of a variety of chemicals.
  • The sum total of all chemical reactions occurring in an organism due to specific interactions amongst different types of molecules within the interior of cells is called metabolism (Gk. Metabole-change).
  • Metabolism involves the transformation of matter and energy within an organism and their exchange with the environment.
  • All activities of an organism including growth, movements, development, responsiveness, reproduction, etc. are due to metabolism.
  • No non-living object shows metabolism.
  • However, metabolic reactions can be carried out outside the body of an organism in cell-free systems.
  • Such reactions are neither living nor nonliving.
  • The isolated in vitro metabolic reactions can, however, be called biological reactions or living reactions as they involve biochemicals.

4.4 Consciousness or Sensitivity

  • All living beings have a definite shape and size, which get modified to some extent when growth occurs.
  • All living beings are thus called ‘amorphous’ i.e., having definite shape, while non-living beings are called ‘amorphous’ i.e., not having definite shape. 
  • It is awareness of the surroundings and responding to external stimuli.
  • The external stimuli can be physical, chemical, or biological.
  • The stimuli are perceived by sense organs in higher animals, for example- eyes, ears, and nose.
  • Plants do not possess such sophisticated sense organs.
  • However, plants do respond to external factors such as light, water, temperature, pollutants, other organisms, etc.
  • Photoperiods influence reproduction in animals and plants that breed during particular seasons. 

4.5 Homeostasis

  • An internal environment suitable for the functioning of body organs is present in every living being.
  • It is quite different from the external environmental changes in the external environment do not have much impact on the internal environment as the living beings have a self-regulated system to adjust and maintain the internal environment.
  • The phenomenon is called homeostasis (Gk.homois-alike, stasis-standing).
  • Homeostasis is also present in each cell of a multicellular organism.
  • It shows homeostasis or the ability to maintain a perfect internal environment through a self-regulated system. 

4.6 Energy

  • Living being constantly requires energy not only to perform various activities of the body but also to overcome entropy or the tendency to randomness.
  • The source of energy is food.
  • It is required by every cell of the body.

4.7 Cellular Structure

  • Each living being is a complete entity, which is formed of one or more cells.
  • The cells are made of protoplasm, popularly called living matter.

4.8 Shape and Size

  • All living beings have a definite shape and size, which get modified to some extent when growth occurs.
  • All living beings are thus called ‘amorphous’ i.e., having definite shape, while non-living beings are called ‘amorphous’ i.e., not having definite shape. 

4.9 Movements

  • Living beings show the movement of their parts.
  • Some are able to move from one place to another.
  • This phenomenon is called Locomotion.

4.10 Variations

  • Living beings possess variations and have the ability to evolve with time.

4.11 Adaptations

  • Adaptations are the variations that help living beings modify themselves and show perfect harmony with changed surroundings.

4.12 Organisation  

  • A living being has an organization, i.e., the living being consists of several components, which cooperate with one another for the well-being of the whole organism.
  • Each level of organization has its own properties, which are not found in its constituents.

4.13 Regulation

  • A control system works in every organism which helps in the regulation of body functioning like growth, excretion, development, reproduction, and other metabolic activities. 

4.14 Irritability

  • All organisms respond to stimuli in their environment and this property is called irritability.
  • The stimulus and response may be either simple (for example- the movement of a unicellular organism towards a light source) or quite complex such as a bird responding to a complicated series of signals in a mating ritual.
  • organism towards a light source) or quite complex such as a bird responding to a complicated series of signals in a mating ritual.

4.15 Evolution

  • Organisms have a tendency to evolve with time due to the accumulation of various types of variations.

4.16 Interactions

  • Interactions occur among the levels of organization within organisms and between organisms and their external environments.
  • The levels of interaction between organisms and their environment are those of populations, communities, ecosystems, and the biosphere.

4.17 Emergent Properties

  • The appearance of new characteristics at a given level of organization is called emergence
  • Actually, an organism is more than just the parts of which it is composed.
  • Unique properties emerge from interactions within an organism at its various levels of organization and from interactions with its environment.

4.18 Life span and Life Cycle

  • All organisms have a definite life cycle for itself which is completed in a particular period or life span.
  • The life cycle of living beings includes birth, growth, reproduction, and thereafter death.

4.19 Death

  • Death results in the loss of life.
  • The organism reproduces to compensate for the loss of life.
  • Death is a device for the recycling of elements between living and non-living matter and such recycling helps to maintain the balance of matter in nature.

5. Is a Virus Living or Non-Living?

  • The virus is an intermittent link between living and non-living.
  • They possess both the characteristics i.e., living (they tend to infect other organisms) and non-living (viruses cannot reproduce without a host) things.