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| Open System, Steady State, Closed system and Homeostasis |
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 Any system where there is a constant exchange of matter and energy from the surrounding environment is called as open system. |
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All living organisms represent open systems. |
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Any state of a system where the rate of input of energy and matter is equal to the rate of dissipation of energy and output of materials, is called as a steady state. |
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Open systems such as living systems always tend to exhibit a steady state. |
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| fig. 1.3 - Living system |
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The living system always tends to remain in a steady state with the help of a self regulatory mechanism. Such a phenomenon, which involves maintenance of a constant internal environment is known as homeostasis. |
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| Some examples of homeostasis from everyday life are: |
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When we enter a darkened room from bright light, we are unable to see anything for a few moments. Within a few seconds we are able to adjust our sight to the dim light and move about easily. |
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After vigorous exercise, the body temperature rises and there is profuse sweating. Evaporation of the sweat results in cooling which brings down the body temperature to normal. |
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In winter the skin contracts to conserve body heat. |
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The homeostatic mechanism works through a negative feedback mechanism where the rate of formation or utilisation of any product is regulated by the amount of that product available at a given period of time. |
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The homeostatic mechanism operates at all levels of hierarchy in the living system, namely cells, tissues, organs, organ systems and organisms. It occurs in almost all forms of life and contributes to a balance in nature. |
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A closed system is one in which, there is no exchange of matter and energy with the environment. Eg., Crystals of sugar, stones etc. |
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