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What is Life? Describe the main properties (Characteristics) of living beings.

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It is very difficult to define Life. The study of life is called Biology. All the substance of the world divided into two categories

  1. Living &
  2. Non-living

On the basis of certain features. We divide the living and the non-living substances.

Main properties of the living forms :

  • Definite form and size : Each living being usually has a definite form and characteristics size, it is an organised individual with a centralized control and independence of its parts.

e.g. Frog, Horse, Crow, Plants etc.

But there is no limit to form or size of non-living substances and they have no centralized control.

e.g. water, sand, wood etc.

  • Cellular Structure : The body of living beings is composed of many small units which are called Cells. 

Inside every cell there is living material, called Protoplasm. Every action of living being is controlled by protoplasm.

Therefore, protoplasm is called Physical Basis of Life.

Non-living substances may have the same elements as found in protoplasm but they have no life.

  • Nutrition : Living-beings require nutrition of food which is used for building the body and rejuvenating worn-out parts, and also for supplying energy of their vital activities.

Living beings take food in the form of solid or liquid.

e.g. Proteins, Carbohydrates, Fats, Water etc.

But non-living substances need no nutrition though a non-living body such as a motor car required fuel for its energy.

  • Growth : Growth is a major feature of a living being. Constant nutrition forms new protoplasm which results in growth or an increase in size and weight.

There is no growth in non-living materials. If growth occurs in non-living objects, such as a crystal, it is due to the addition of material on the outside. This material is chemically the same as the non-living object.

  • Respiration : Respiration is one of the chief feature of living beings.

The systems of respiration in plants and living being are mainly the same. Respiration consists of inhaling oxygen from air or water and utilising in the living body.

The oxygen then forms waste CO2, which is eliminated from the body.

Several complex chemical changes take place in respiration which include production of energy by oxidation of food. But there is no respiration in non-living objects.

  • Reproduction : Reproduction is a unique property possessed only by the living beings.

Each living organism has the ability to duplicate itself or produce new individuals resembling it in all essential features.

They reproduce by using their own body material.

But, non-living substances cannot reproduce.

  • Excretion : Certain compounds of nitrogen, water and carbon dioxide (excretory products) are constantly formed in the living body, More than required excretory products are harmful to the body.

They have to be get rid of the elimination of nitrogenous wastes is called excretion. No excretion occurs in non-living substances.

  • Metabolism : Various vital chemical changes take place constantly in living organisms. These changes are collectively called metabolism. 

These chemical changes possess two forms

1. Anabolism &

2. Katabolism.

1. Anabolism : The constructive process of organism in the food and oxygen to form molecules of protoplasm, is called Anabolism in which chemical energy is stored as potential energy.

2. Katabolism : It is destructive process in which waste substances such as Urea, Salt water and CO2, are produced. It is destructive process is called Katabolism in which loss of weight, fatigue, hunger and thirst result.

There is no metabolism in non-living substances; if they show locomotion, the energy comes from an external source.

  • Movement or Locomotion : Every living being has movement, we can see clearly in animals.

e.g. Flying birds, jumping of frogs, swimming of fishes etc.

Non-living has no movement.

  • Irritability (Sensitivity) : Every living being has Irritability or sensitivity.

The capacity of an organism to react to stimuli constitutes its irritability. The stimuli may be external (such as heat, light, chemical substance, pressures or gravity) or they may be internal (such as hunger, thirst, pain.)

Irritability or sensitivity is not found in non-living substances.


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