explain how the anomalous behaviour of water on heating and cooling protects the aquatic life.
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Answer:
In cold weather, when the atmospheric temperature starts falling below 0 degree Celsius, water at the surface of a pond initially at temperature above 4 degree Celsius, begins to radiate heat to the atmosphere, so the temperature of water near the surface starts falling . When temperature of water at the surface falls below 4 degree Celsius, water contracts and its density increases and therefore, it sinks to the bottom. This continues till temperature of entire water reaches to 4 degree Celsius. Now, further cooling of top layers below 4 degree Celsius results in expansion of water and so its density decreases. As a result, water does not sink further, but it remains on the surface. When the temperature of atmosphere falls below 0 degree Celsius, water on the surface loses further heat from the atmosphere and gradually freezes into ice, but water below ice layer remains at 4 degree Celsius. The water layer just below the ice in contact with it will be at 0 degree Celsius. Figure shows of ice at the surface of pond. Since ice is poor conductor of heat, so ice now prevents the flow of heat from water of pond to the atmosphere. Thus, temperature of water in contact with ice is at 0 degree Celsius, while the temperature of water layers below ice gradually increases to 4 degree Celsius. As a result, fish and other aquatic creatures remain alive in water of pond , though water on the surface has frozen into ice. Nature thus protects the aquatic life during the winter season .
