In humans, the maintenance of a stable internal temperature is a direct result of Homeostasis. Homeostasis is the ability of the body to maintain an equilibrium condition within it's internal environment even when dealing external changes. Homeostasis happens in human when there is an effort exerts by the body to regulate it's internal temperature around 98.6 degrees Fahrenheit. For example, during summer days we produce sweat for our body to cool off, and during winter we shiver for our body to produce heat.
Because it is polar and it is to large to cross the membrane and because the concentration gradients are to strong so they have to be diffused.
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