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Ahmed and Sarah were discussing what life is and what is it meant by living. Ahmed said that "Something which exhibits growth, development, responsiveness and other life characteristics is called as living". Sarah added that "Life is a characteristic quality that differentiates inanimate objects from animate forms".
What is "living", and what is "life"?
Life is a complex organisation of molecules that expresses through chemical reactions, leading to growth, development, adaptation, responsiveness and reproduction.
Living beings exhibit growth, development, responsiveness and other characteristics of life.
Living beings have structure, shape, size and form. Based on these, living things can be recognised as prokaryotes and eukaryotes.
In contrast, specific shape, size, and structure are present in non-living objects, like brick or rock. Thus, a single trait of life is insufficient to distinguish a living being from a non-living things. Therefore, several traits are discussed to differentiate living beings.
Criteria to decide living beings:
The essential characteristics of living beings include:
1. Cell Structure: It is a defining property of living beings. Each living being is formed from one or more living units called cells.
2. Metabolism: All organisms perform chemical reactions. Metabolism is a defining property of living beings.
3. Growth: Growth is a permanent, irreversible and measurable process in both animate and inanimate objects. In animals, growth occurs until a certain age, while in plants, growth occurs throughout its life.
4. Consciousness: Consciousness is an exact defining property of living beings. All the organisms can sense and respond to the stimulus.
5. Organisation: Living being has multiple levels of organisation that starts from cells to ecosystem.
6Reproduction: Producing the offspring that are biologically and genetically similar to parents is called reproduction.
7. Movement: Different types of living beings can locomote in a variety of ways. Eg., Amoeba locomote by pseudopodia.
8Adaptation: Living beings adapt and adjust according to the environment. Adaptations allow organisms to overcome the changes in the environment.
9. Homeostasis: The steady state in which the internal condition is maintained in accordance with external equilibrium is called homeostasis. It influences organisms life in many ways.

10. Excretion: The removal of metabolic wastes from the body by the organisms is known as excretion. It is also an essential life process.
11. Respiration: It is a metabolic process wherein the organism obtains energy in the form of ATP by inhaling oxygen (\(O_2\)) and exhaling carbon dioxide (\(CO_2\)) by oxidising the complex organic substances.
What are Life processes?
All organisms perform basic functions to keep them alive.
The basic processes essential to sustain life on earth are called life processes.
All life processes together keep the living organisms alive and perform the job of maintenance. The life processes include:
  1. Growth
  2. Movement
  3. Nutrition
  4. Metabolism
  5. Respiration
  6. Reproduction
  7. Transport
  8. Excretion
  9. Control and coordination
  10. Differentiation
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The Life Processes